This summer I had the distinct privilege of participating in an internship for the Society of Physics Students and the American Institute of Physics. I’m working with the American Physical Society (APS) in their Outreach department, on a (VERY VERY COOL) project called “PhysicsQuest“.

I’ll expand on PhysicsQuest and why it’s so awesomely cool in a separate post (which it deserves). For now, I want to discuss a rather amusing incident that happened the other day at the office.

Something’s Fishy

I had some work to finish and I decided to stay late. As I was working on my extension activities and trying to devise physics experiments to do at home (familiar?) I noticed the team leader (and my internship mentor), Rebecca Thompson, carrying a fish tank, half full of water, out of the office and towards the kitchen.

She was walking really really slowly, carrying the big tank with both hands carefully, and seemed to make an actual effort to walk steady. I turned and asked if I could help, thinking the tank must be extremely heavy, to which she replied with one of the best physics comments I heard to date:

“It’s not that heavy, but my walking pace matches the resonance frequency of the tank, so I just have to walk slowly.”

Ha! Brilliant! See, most people would simply state “If I walk too fast, water will splash all over me.” But that wouldn’t have been physically accurate, and Becky would have none of that. She stood firm to Physics - and explained it much better.

Resonance Frequency and Fish Tanks

Her explanation was, of course, absolutely right. The ‘usual’ explanation makes the connection between the splashing of the water to the speed of the walk, and that’s not entirely accurate. You could, theoretically, walk faster and still not get splashed, if you manage to walk at a steady pace, not hit anything, and avoid the resonance frequency.

Resonance-wha?

When an object oscillates back and forth steadily, we describe the movement as having a frequency. The frequency is the number of repetitions per certain amount of time. So if an object oscillates back and forth three times per second, we describe the movement as having that frequency of motion: Three oscillations per second (or 3 Hz).

When the fish tank is moved or shaken, the water inside it oscillates back and forth, creating a recurring wave that bounces from one wall of the tank to the other. This wave has a certain frequency, and assuming the walking pace of whoever carries it remains constant, the frequency remains more or less constant as well.

But frequencies also have this unique little phenomenon called “Resonance”. The wave inside the tank overlays itself. Most of the time, the overlaying waves would cancel a small bit of one another, keeping the water well inside the tank. But if the frequency is just right, the recurring waves build-up, and the amplitude (or, in this case, the height of the splashes) increases more and more and more and— you get soaked with fishwater.

Resonance Frequencies. Source: Wikipedia (http://en.wikipedia.org/wiki/Resonance)

For Becky, her normal walking pace creates vibrations that match the resonance frequency of that size of tank, causing the waves inside to increase and increase…. dangerously close to splashing her completely.

Changing the Walking Pace

There are two ways to avoid this resonance frequency - either vibrate the tank slower (as she did by walking slowly) or vibrate it faster. Of course, vibrating the tank faster than the resonance frequency would, in theory, prevent the waves from adding-up dangerously, but it carries the additional risk of either bumping into something (oops) or shaking the tank uncontrollably and having water splash on you regardless of frequencies.

She made the safer choice. And she remained dry. And completely physics’y!

Other Examples of Resonance Frequencies

Resonance frequencies aren’t just about water. They are relevant in many aspects of our lives, especially when new buildings and bridges are built. Whenever something vibrates your new construction, you need to be careful about resonance frequency. Even if your bridge is tough enough to sustain a large amount of weight on it, if the objects on it create vibrations that are exactly right (or, in this case, exactly wrong), you can have a serious problem.

There are a few examples of this actually happening in real life. I didn’t have a camera when Becky carried her fish tank, and I doubt she’d have agreed to a demonstration*, but there are a few videos online that show this principle in much larger scale.

The Tacoma Bridge Disaster

One example of resonance frequency gone bad is The Tacoma Bridge disaster. The original Tacoma Bridge was a suspension bridge built in 1940 in Washington state. It dramatically collapsed less than a year after it was opened.

On the morning of November 7th, 1940, winds were high across the bridge, reaching around 64 km/h (40 mph). This in and on itself probably wouldn’t have been enough to collapse the bridge, but the problem became much worse when the structure began oscillating back and forth like a pendulum. When one side of it would go up, the other went down, and repeated to the other side; this movement back and forth became more and more pronounced, as the bridge reached its resonance frequency.

www.youtube.com/watch?v=dm0XXuFt30k

As you can see in the video above, the Tacoma Bridge had these ‘swaying’ oscillations much before the disaster occurred. The day of the disaster, however, the oscillation frequency reached exactly that of the resonance frequency, and instead of remaining at a small amplitude, the vibrations increased until the bridge broke.

Here’s a great video summarizing the Tacoma Bridge disaster, including the physical explanation:

www.youtube.com/watch?v=3mclp9QmCGs

Walk Carefully

Theoretically, then, Becky could have simply run forward with the fish tank to avoid the resonance frequency. That probably would have resulted in shaking the water tank uncontrollably and having herself splashed anyways, so her choice was the best one.

Now, when you carry big containers of water, you can plan your walking pace accordingly! Does the water start splashing higher and higher? try walking at a steady pace, either faster or slower, and avoid the splashy power of the resonance frequency.

* Although it was, in all honesty, a very hot day, I doubt she’d want fishy water all over herself, even for physics’ sake.

Sources and More Info

• Waves: http://en.wikipedia.org/wiki/Waves
• Resonance Frequency: http://en.wikipedia.org/wiki/Resonance
• Tacoma Narrows Bridge: http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)

Thanks

These updates are available in the SPS National website.

SPS Interns 2011 in front of The White House

2nd Week, June 10th

Another Physics week just ended and we’re on our way to our third week. Wow. I know it’s a cliche to say time flies (not to mention it’s not very physical), but it sure felt like it. During the weekend we decided to do the tourist thing and visit museums. We ended up walking half of Washington DC’s waterfront on foot and then visited the Air and Space museum and watched their Hubble 3D IMAX show. In the evening, tired but happy and extremely hungry, we decided to cook dinner together and watch a movie. We all made something for the dinner; I made my famous vinaigrette sauce for the salad, but people seemed to prefer the store-bought Feta sauce. I refuse to take it as a hint.

The week was super exciting too. I managed to experiment with quite a number of extension demos and find a few REALLY cool ones I’d like to try for next week. Becky is going to be at some convention so I will be on my own, free to roam the kitchen and destroy plastic utensils and paper cups. We made sure I have a list of “todo”s, which, I have to say, look much better on paper than they do in reality. I need to work on the write ups for the demos I already tested and transform them to Middle-Schooler-safe perfectly understandable quick summary while keeping it engaging and avoiding the ever-so-boring cookbook-style. It’s a lot harder done than thought-of. I just hope I manage to finish them before the end of next week.

On Tuesday evening we all went to a Science Cafe in the NSF building in Arlington. The lecture was very interesting, and I think Anish (who is supposed to arrange some of those himself during the summer) got quite a lot of ideas and some feedback from us. Also, the burgers were awesome. Food and science always work so well together. Sometimes too well. I’m going to have to hit the gym extra this week!

On Friday we met the SPS Executive committee today for lunch, and we will again for dinner followed by a “Capitol Steps” show. They’re great, I already follow them a little through their website, so the evening is bound to be exciting; you will have to wait for next week to hear how it was, of course. Reverting to the beginning of this entry, time doesn’t really fly.

Well… maybe it does, if one second per second counts as flying.

3rd Week, June 17th

This week was so full of events, I don’t even know where to start.

I will be a good physicist and start from the convenient middle, then move back and forth in time.
Wednesday night the wall-mounted mirror in our dorm room decided to test the theory of gravity, a test that resulted in it crashing loudly into the floor and, in the process, shattering to hundreds of reflective shards. It appears gravity was unfazed.

Cabot certainly was, though. He (and I, along with Amanda and Courtney who was also in our room) had to take a moment to recover our beating hearts from somewhere in the basement. The shock was quickly transformed into a conversation about the structural integrity of drywall and the fact that Cabot became stranded in our room now, since he was, unfortunately, barefoot. No worries, though. Amanda made some food and Courtney recovered his shoes while Amanda and I ended up waiting till almost 1am for maintenance to come and save us.

We went to bed really late after a rather exhausting day — but I will get to that in a bit.

I will digress to the beginning now. The weekend was absolutely awesome. The Capitol Steps show on Friday evening was hilarious and we all had a lot of fun. Then on Sunday we walked around Georgetown and ended up waiting in a 45-minute line to get cupcakes. Let me tell you, though, 45-minute-line cupcakes are worth it. They were awesome, and I’m rather happy they require some level of effort to purchase, otherwise I think I’d be eating them much more often, and, quite possibly, ending up looking like one.

Must exert effort for cupcakes. I think I discovered the law of cupcakedynamics.

On Monday we went to Tuckahoe Elementary School to help Amanda and Erin with their activity about Rutherford’s discovery of the nucleus. We had two groups of 3rd graders that simply blew our minds. They were cute and terribly smart. When Amanda asked them what was the smallest thing they knew, we didn’t really expect one of them to yell back “quarks!”. A little physicist in the making! It was such a rewarding experience. The kids seemed to really enjoy the activity, and Amanda and Erin were brilliant. The activity they devised was a complete success, at least for the 3rd graders.

On Monday evening, we went to a science cafe with Joe Palca about his book “Annoying: The science of what bugs us”, which he wrote with Flora Lichtman. It was a lot of fun, and the discussion was great. I also ended up buying the book (I have a little sister, I have to learn the craft) and getting it autographed. Yay!

Tuesday was my first day of the week actually doing work. Becky was out the entire week at a convention out of town, so I had a list of “to-dos” to accomplish. I was so worried I wasn’t going to successfully finish them by the end of the week, that I spent a good portion of Tuesday and Thursday in front of my computer, typing and revising. The fourth floor had a day off of my experiments, though. Despite the incredibly busy and hectic week, I think it was quite productive. I now have seven finished activities that are waiting for Becky to go over them, and I continued to make another list for a few more exciting demonstrations on the subject.

Erin and Amanda had to adapt their lesson to teenagers, since on Wednesday we went on to deliver the same type of activity (revised, of course) to two full classes of 7th graders. Middle-schoolers are much more of a challenge to engage than elementary school kids. It was exhausting and quite different than the younger children, but I thought Amanda and Erin did a great job changing the lesson plan for the older kids. Even the teacher said they were more engaged than usual, and for teenagers, that says a lot. Well done Amanda and Erin!

The day was topped off by a picnic at ACP followed by an egg relay and an open mic, which proved once and for all that physicists are, in fact, quite talented people. At least those who went up to the stage. It was pretty impressive! In the evening we went to have Frozen Yogurt at an outdoor concert in Farragut square – an awesome finish to an exhausting day.

Thursday and Friday were full work-days in the office for us, so I managed to finish my list of to-dos and work on some ideas on more home experiments.

I will take this moment in time to apologize to the fourth floor of the ACP building, and in particular those of you who require the continued use of the kitchen refrigerator. I promise, the balloons and colorful ice cups will be taken out by next week. Or by August, the latest. Promise.

It is now Friday evening, and there is one more really cool thing that just happened: my business cards are on the PhysicsCentral Physics Buzz Blog. How amazing is that? When I made them, I wanted people to have a reason to take them out of the stack at the end of the day (or at the end of a busy convention) and remember who I am, so I made sure there is a little science experiment that goes along with the card. With only the help of a few folds and liquid soap, it transforms itself into a racing boat, demonstrating the principle of surface tension and surfactants. The guys here at the office (who, incidentally, write for PhysicsBuzz blog) thought it would be a great blog post. I’m so honored!

Of course, as I said in the first journal entry, I live and learn. Next time I make these cards, I will make them waterproof.

Here’s for another incredible week!

2011 SPS Interns with John C. Mather at the American Center for Physics, MD

I finished my absolutely last undergraduate physics final on Thursday in Thermodynamics, and had just enough time to pack my closet and hop on a train to DC and start my 9.5-week adventure. So far? Awesome.

After two days of schmoozing and resupplying ourselves, all 9 of us interns traveled to the ACP building in MD for our orientation. We finally put faces to the people we communicated with, got to learn a lot about what they do, what we’re expected to do, and what we’re expecting they’re expecting us to do. We also went home with some wonderful ‘goodies’ like diffraction glasses (which I did not take off for most of the day, and still walk around in, looking at rainbows everywhere) and the GalileoScope. We have to find time and a clear night to test it out properly now.

We had our first-day lunch with Nobel Prize laureate John C. Mather, and got to hear his stories about how his research evolved from an interesting question to building actual equipment that went out to space to a Nobel Prize. That was pretty cool.

Overall it was a great first day, and at its end we each went to our respective departments to get started. Anish, Erin and Amanda are together in the second floor (in the SPS/AIP) while I’m on the fourth (in the APS), so we get to commute together and see each other every day for lunch.

Colorful density rainbow!

APS outreach group and particularly the PhysicsQuest project is amazing. I get to design extension experiments about Thermodynamics and heat. Good thing I just finished that exam on Thursday! Heat seems to follow me around. But I am happy about that, I love the subject matter and I am very excited to turn my theoretical ideas into practical experiments that can actually work in the classroom and at home.

Of course, that turned out to be easier said than done. Reality? Not like theory at all. Forget undergrad lab where everything is laid out in steps – I need to actually design these steps now from scratch and make them middle-schooler-safe. And apparently, there are no spherical chickens walking around people’s kitchens, so experiments that totally work in theory (and calculation, and force-diagrams, and graphs and discussions) can utterly fail in reality for the silliest things sometimes. Sure, you could, in theory, compare the density of boiling water to that of ice-water by measuring the level of a floating item, but can you do it without boiling your fingers? Not as easy anymore. Also, just in case you’re wondering, some plastic cups melt with hot water. I have tested this hypothesis without even realizing I posed it. I assure you, it’s verified many times over. I was already notified that these are all expected here, and it seems they’re a sort of ‘rite of passage’ in the department, so I guess there’s a bright side to the fails.

So, yes, work is very challenging, but it’s also a lot of fun. These are exactly the things I love doing in Physics – on one hand, find the greatest and most engaging way to demonstrate a physical phenomenon, and on the other make sure it’s accurate, it works, and it’s kid-safe.

Insulators, Brrrrr..!

I already have two experiments I’ve tested and written up, so I think that’s a nice accomplishment for the first week. Becky needs to go over them both, so I can’t really be sure they’re good just yet, but I think I’m getting there. I have two more demonstrations that I’m about to test and I am pretty sure will work. Of course, I was also pretty sure the boiling water one would work, too, and that ended up failing. Also, the ice balloons? Not a good idea. Live and learn, though. Live and learn.

Until next week: Vini, Vidi, Physics.

Note: This entry is also published in the Society of Physics Students website, here.

This semester I started tutoring in the physics and math study center. I am the only “pure” physics tutor – the rest of the tutors are mathematicians or engineers who feel very comfortable with mathematics (justly so, they’re all quite awesome). Most of them shy away from physics problems, though, letting me – and a handful of other tutors – deal with the dreaded subject.

In general, physics seems to have this aura to it that scares people before they even start solving a problem. This begins with very basic physics, but continues with higher level material. The difference seems to be that only those who like physics – and find a good way of dealing with it – stick around to deal with the higher level stuff.

Physics? Oh Noes!

Physics – and most science subjects – can be very complicated. Describing our world is not always intuitive, and sometimes requires a mathematical and conceptual understanding that is very advanced. That much can explain why not everyone goes for a physics career. That and, well, the salary.

In basic physics – material covered in high school and low level university courses – the methodology is straightforward. There’s no need to panic. Quite often, it’s the panic itself that prevents students from dealing with the subject carefully and getting the most out of those courses.

What’s the Strategy?

In my experience tutoring for (and taking) low level physics classes, I have worked out a few ground rules that can help you conquer problems. These will help whether the problem is in a homework assignment or on an exam. We will go over them now.

1. Don’t Panic.

Sounds obvious, right? And yet, it’s harder than it sounds. You look at the question and the sentences loom at you menacingly, confusing you to no end. You have no idea where to start, even if you recognize the basic concepts. Whose cars go in which direction? What type of wave travels on the string? Help me, you think in terror. Help me…!

This is your time to take a deep breath, close your eyes, and count to five.

In lower level physics, most questions can be solved by simple formulas. As long as you remember these formulas, you are most of the way to an answer. From now on, the only thing that you need to concentrate on is converting the horrible, confusing chunk of text into readable bits that fit into your formulas. You can do that.

2. Try to Understand the Situation

What is going on in this problem? Is this a ball free-falling from some height? Is it Superman’s velocity as he flies to save Lois Lane a certain distance away? Or perhaps it’s a question about magnetism? Electricity?

Figure out the context first. You don’t have to understand all the small details, but once you know what you’re dealing with in general, you will know how to formulate your answer and which equations to use.

3. Read the Question Carefully

So you understand the physical situation now, and you know what subject this question deals with (or multiple subjects). Now, read the question again, and make sure you are clear on what it actually requires you to find. The same type of problem – say, bouncing ball – can ask you to find initial velocity, maximum height or angle of launch. Each of these will require a slightly different strategy. Make sure you know what you need to do.

Another good tip to remember at this point, too, is that many physics problems have very crucial information in the wording. A car starting from rest, for instance, means your initial velocity is zero. Two objects falling from a window might behave differently if they are both attached to one another.

Read the question carefully – this isn’t the time to skim. Make sure you don’t miss crucial information.

4. Organize the Information

Word problems are confusing only because they hide the actual variables inside them. Sometimes, you will be given extra information that you won’t really need. Other times, there will be variables whose purpose is revealed in a later part of the question.

For example, if the question has a car that starts to move from rest and takes 5 minutes to reach a speed of 20 km/h, you should write down the basic variables like so:

• v(initial) = 0 km/h
• t(final) = 5 minutes
• v(final) = 20 km/h
• a = ?

Do this with all the information you get out of the question. This will help you see the variables in front of you clearly, find the proper equation to use, and see what you’re missing. It will also make the original, confusing text unneeded. If you organize your information, your brain will be free to deal with actual physics instead of reading comprehension.

5. Sketch the Scene

In physics, drawing a picture can really make things easier. For example, getting a visual idea of your frame of reference, or of the difference between up (positive) and down (negative), can mean the difference between a right answer and a wrong one.

You don’t have to be good at drawing. Draw a rough schematic according to the situation. Arrows are your friends in physics questions – they show you which direction an object is moving or what the possible sum of forces applied to it are. They organize the information for you. Use them.

Some questions already come with a drawing – use it! Questions about forces, for example, are best solved by schematic, and you can miss some crucial information that you don’t immediately see if you don’t sketch it.

Go on, Picasso, give it your best shot, and move on to the next step.

6. Verify Units

Sometimes your professor will test your unit conversion skills. That isn’t without a purpose – in physics (and science in general), units are crucial. You have to make sure your units are the same throughout the exercise, otherwise formulas will not work. If you multiply velocity by time, you will get the distance (assuming constant acceleration), but if the car moved at 10 km per hour for 5 minutes, multiplying 10 by 5 will not give you the right answer. Rather, you will need to either convert the kilometers per hour to kilometers per minute, or (and probably easier) convert 5 minutes to units of hours.

The best way to do this is by fractions, but there are enough unit conversion guides out there that explain this concept. Remember not to panic, do it carefully and you will get your correct values.

If we continue our example from the last part, we should convert the t(final) from minutes to hours. This isn’t too hard to do:

(See how the ‘minutes’ units are canceled with the ‘minutes’ units in the denominator, leaving the ‘hour’ units with the final answer? that’s a great way to check that your conversion is right)

Now that all your variables are in the correct units, you can continue solving the question.

7. Consider Your Formulas

This is true for most of physics questions, and absolutely true in the lower level physics. As a student of basic physics, you are not expected to reinvent the wheel – or even understand how the wheel was invented in the first place. What you are expected to do is to understand the concepts and use the tools available to you.

The most important of those tools are the formulas.

Some professors will require that you memorize relevant formulas, while others will give you a “cheat sheet.” Either way, you have what you need. Memorization might sound horrible, but most physics subjects don’t have that many equations to memorize. I remember taking an advanced electromagnetism course where I had to memorize about 20 different formulas. At first it seemed terrible, and I kept remembering them wrong. However, the more you use the formulas, and the more you understand what they mean and – if you care enough to check – where they came from, the easier it gets to remember them.

Organize your formulas in front of you. If you have a cheat sheet, align it next to your variables. What formula can you fill up, leaving the least amount of missing variables? Which formula can help you solve the question?

See it? Use it.

But Wait, Which Formula Do I Use?!

You look at your formula sheet and you have three different ones that are marked under the problem’s subject. How do you know which one to use?? Naturally, you begin panicking again.

Don’t panic.

Physical equations didn’t just land on scientists from the sky, all wrapped up nicely in mathematical formulation. They are derived from physical properties, and they are all interconnected. In most physics problems, there is more than one way to reach a solution, often meaning that more than one equation can work. In fact, in the vast majority of questions, no matter what equation you use – assuming that it is relevant to the subject matter, and that you insert the proper variables – you will reach a solution.

The way to know which equation to use depends on two main issues: the variables given to you in the equation and your experience. The more problems you solve, the more you will become familiar with strategies for picking the right formula. Until that happens, though, look for the formula that has the variable you already know (from your list of variables) and connects those to the one variable you are missing. If you have two missing variables, you will likely need two equations.

Slow down, look at your variable list, and find the right ones. It’s like a puzzle, and the more you do it, the better you get at it.

8. Solve

You have your variables, you have your sketch, you know what’s going on – plug in, solve and get your answer.

Just remember: you might end up with a relatively lengthy equation to solve, or sometimes two (or more). Don’t forget your goal. Keep glancing over at your list of variables. See that little variable marked with a question-mark, noting the one you’re missing? That’s the one you need to solve for. Focus. Keep the goal in mind. Solve the equations.

Now breathe.

9. Verify Your Results

This is a step many students skip, and then pay for. I paid for it dearly in my high school final physics exam, in fact, and I will never do it again. Verifying results can be as easy as skimming through your equations and taking 15 seconds to think about the answer you got.

That can make the difference between 100% and 70%, and sometimes worse.

What do I mean by verifying the result? Well, if the answer you got for the velocity of your car is more than the speed of light, you’re likely wrong. If the units of acceleration come out to be anything but the proper distance/time^2 units, you made a mistake. If your question asks for minutes and your answer is in seconds, you missed a step.

Read the instructions carefully and verify your method. It really is important.

10. Practice. Practice. Practice.

Yeah, yeah, yeah, you think to yourself right now, I bet. Everyone says it. Practice makes perfect. Practice to become better. How.. obvious.

But it doesn’t seem to be properly obvious to many students.

I sometimes get amazed looks from the students I tutor when I come up with the perfect way to solve a question they just spent half an hour trying to solve. “I would have never thought of it!” they exclaim, in awe of my genius. Well, as much as my ego would love to accept this compliment, I am no genius. The reason I see the solution quickly is usually because I have experience – I did so many of these questions that I already anticipate which method would likely work best.

Am I right all the time? Of course not. Sometimes I start with one method and find it was the wrong way. But those “errors” only serve to teach you how to approach different sets of questions. The more you do them, the less time it takes you to recognize the actual effective way to solve them.

It’s all about experience. Don’t panic and don’t give up. Physics is less hard than you think (most of the time).

Example Problem and Solution

So we’ve tried to construct a method of attacking general physics problems. Let’s see how this works in practice by choosing a sample question I picked up from this online document.

The Problem

A man drags a box across the floor with a force of 40N at an angle. The mass of the box is 10kg. If the acceleration of the box is 3.5 m/s^2 (and friction can be neglected) at what angle to the horizontal does the man pull?

Strategy

1. Don’t Panic.
2. Try to Understand The Situation
   In this case it’s fairly straightforward. A man is pulling a box on the floor, only he’s pulling it at an angle. The box is accelerated forward.Since we’re only told about the forward acceleration, we will need to consider the horizontal forces (or the horizontal projection) – the vertical projection doesn’t seem to be relevant to this problem for now.
3. Read the Question Carefully
   In this case, the question is short, and it’s hard to miss data. Still, we recognize that we have some force on the box, and that we are expected to find the angle of that force. Now we know what we need to do, and we can move on to the next step.
4. Organize The Information
   Here’s a list of our variables:
   1. Force(man) = 40N
   2. m(box) = 10 kg
   3. a(box) = 3.5 m/s^2
5. Sketch the Scene
   In this case, there already is a drawing in the original document, but I left it out on purpose. Try to sketch it on your own. We have a box, a force pulling it at an angle. Like this:
   
   
   Now we can see what we are expected to find, and what we already have.
6. Verify Units
   All of our units fit in this case. No need for conversions.
7. Consider Your Formulas
   Well, these are the main formulas that deal with basic forces:
   1. F=ma
   2. 
   3. 

   Formulas #2 and #3 are the deconstruction of the force vector (if you don’t know what that means, you should go over the material) – these are the formulas that link the force (which we know) to the angle (which we want to find out)

8. Solve
   Remember our “Understand the Problem” part? We said there that since the acceleration is on the horizontal, we will need to consider the horizontal force or projection of that force. And we know that F=ma, which means that the acceleration is a direct result of the force. What is the force on the box, then?
   

   This is the force responsible for the acceleration – and since the only force at play is that done by the pulling man, this has to be the horizontal projection of that man’s force.

   Remember our trigonometric formula for the projection? Let’s take the horizontal component, and plug in what we have:

   

   

   

   

   

   Which is our answer.

9. Verify Your Results
   Well, let’s think about this for a moment. The man pulls the rope with an angle. But the projection (35N) is not too far off of the actual force he uses (40N) – it’s quite logical, then, that the angle will be relatively small – even smaller than 45 degrees.

Psst… You’ve done it!

Summary

Don’t let the subject bog you down before you even tackle it. Physics sounds horribly complicated, but most of its basic level questions are similar – once you get the concept, you get the solution.

So, to summarize:

1. Don’t Panic.
2. Try to Understand the Situation.
3. Read the Question Carefully.
4. Organize the Information.
5. Sketch the Scene.
6. Verify Units.
7. Consider your Formulas.
8. Solve.
9. Verify Your Results.
10. Practice. Practice. Practice.

There. That wasn’t so bad, was it?

It’s about experience, confidence and organization. Study the material well so you understand the concepts (even if you hate the math) and understand the equations you need to use. Tackle the problems patiently and with organization, and you will see how you suddenly become good in physics. Maybe even very good. Heck, maybe you’ll make it your university major!

Do you have any more advice on how to approach physics questions? Do you run into problem regularly with certain types of problems? Add your input in the comments!

Credits

• UnintentonalChaos, for incredibly awesome editing help.
• Daniel Grrrrrrrrrrrrrrrrrrreenberg, for his (as usual) keen eyes and good advice.
• For Toby, for pointing out the final corrections even though she doesn’t quite like physics (no one’s perfect).
• Picture credit: RLHyde from Flickr.

Picture by joelwillis via Flickr (Creative Commons 2.0)

I usually don’t like making grandiose statements ahead of myself, like “Astrology is totally unscientific”, because I prefer leaving the benefit of the doubt until I check the claim. In the case of Astrology, however, there’s no use pretending.

Astrology isn’t science. It makes baseless predictions, relies on overly-generalized statements and has a false basic premise*.  You can read this online from various other sources, and there isn’t much use for me to reiterate the points made.

What I am going to do is test the basic premise.

* Phil Plait, “The Bad Astronomer”, has a great analysis of Astrology that goes over all the above, and more, as does the skeptic dictionary and the Astronomical Society of the Pacific among many, many others. You can also watch Australian Skeptics’ Richard Saunders brief live argument with an Astrologer.

Note: For your convenience (and due to popular demand), I added an automatic tool where you can measure the force applied by any object at any distance. Test it yourself!

Click here to open the Force Calculator!

(opens as a new window).

The basic premise of astrology

Astrologers claim that the positions of the planets and “Zodiac” signs (constellations of stars) at the moment of our birth – and generally throughout our lives – affect our personality, mood and affairs.

I will not get into the so-called  “metaphysical” effects, a mishmash of misunderstood physical theories (quantum physics, dark matter, dark energy, etc) with some pseudoscientific new-age unfalsifiable claims (from “fate” and “luck” to “planetary energies”, whatever that means). What I will do is treat the claim that astrology has merit in science. Many astrology-believers think that since the planets exert gravity, they might affect our brains, and therefore our moods.

Many people give the moon as an example. The moon’s gravity is known to affect tides – a powerful force we can witness. Many take this as proof that the planets’ gravity is affecting our bodies. On its face, the claim makes sense.

We are going to examine it.

Gravity, the force of masses

Any two objects with mass exert gravitational force on one another. That force is related to the masses of the objects and the distance between them by the formula:

Where G is the universal constant of gravitation, M and m are the masses of the objects and r is the distance between them.

Since we think of planets as incredibly big objects, the idea that their gravity affects our bodies sounds reasonable. But to a newborn, there are other “massive” objects around that exert the same type of force as the planets. They might be much smaller than the planets, but they are much closer, too. If the position of planets at the moment of our birth defines our personality, so should the positions of objects in the delivery room.

This is a testable claim.

The test: planets vs. delivery room

We are going to compare two forces, those coming from the planets and those coming from objects in the delivery room, to reach a conclusion:

• If the forces from the objects in the delivery room outweigh those from the planets, then astrologers should, at the very least, ask the weights and positions of the people in the delivery room when they calculate your chart.
• If, however, the forces of the planets are substantial, then astrology might have some scientific merit. This is what we are about to check.

OMG! Math! Panic!

Relax.

We are about to calculate physical forces so there is some math involved, but you can choose if you want to see it or not. Yes, I’m that considerate.

If you want to go over my math so you can repeat it yourself, add to it (items I missed?) or criticize me (peer-review away, mathematicians) you can reveal the calculations by clicking the “Show the Math” links.

Otherwise, just continue reading the solutions only. Those are useful too.

kthxbai!

One more note: Forces are directional (vectors), but in this case, since we want to calculate the maximum possible force, we will treat them as if they are “lined up”, and therefore calculate them numerically.

What about the mother?

Right, the mother is also in the room, and her body also exerts a gravitational force on the baby. However, The baby is inside the mother, and in her midsection. He is, almost literally*, in her center of mass. For all intents and purposes the mother’s gravity “cancels out” from all directions and there’s no use adding her into the calculation.

* Physicists, stay calm, think “spherical chicken in a vacuum” and bear with me here.

On we go.

The delivery room

Since my intent is to calculate the most basic hospital delivery room, I put in the most basic items that should be found in one. There are likely many more people and pieces of equipment in and outside the room, but the goal of these calculations is a “conservative estimation.”

Therefore, I will ignore the size of the hospital, other people walking by and other large machines that exist in the building. See “Conclusion” for more about those.

Here’s a list of what should be the most basic elements in a delivery room:

People:

• A doctor (obviously)
• A nurse
• OB tech (whose job is to help the doctor and nurse during the actual birth)
• The partner (assuming the mother has one)

Objects

• Bed or birthing chair.
• The machine that beeps (heart monitor).
• Baby crib
• Scale (to weigh the baby, clean and check him or her up)
• Sphygmomanometer (blood pressure monitor) and stethoscopes.

The Calculation

In the following section I will calculate the force exerted on the baby from each of these elements by estimating their weight and mass and their relative distance.

I will assume average-sized staff (75-85 kg), leaning towards the thinner side, to keep my estimate conservative. I will also assume that the baby is level with their midsections (i.e., their centers of mass) which will allow me to ignore their height in my calculation.

Show the Math

Total Maximum Force

So, to summarize (and, for those of you who cared not for the mathematics, to state in the first place):

• The Doctor =
• The Nurse =
• The OB Tech =
• The Partner =
• The Bed =
• Heart Monitor =
• Scale =
• Other Small Objects =

Show the Math

Total Force:

The Planets

EDIT: I have recalculated the forces from the planets. It seems that during the initial calculations I made a rather small (but recurring) conversion error, and due to vigilant commentors, it was properly corrected. You should note, though, that the total force after this re-examination didn’t change. My calculation was fine, I just had a problem with how I wrote it out in the process (in the math part). Apologies.

Now, astrology claims that the planets exert a force on the baby, and their different locations change that force ever-so-slightly to somehow affect the baby’s personality traits.

The idea that the planets exert a force, even on the baby, is true. Whether or not it is canceled out or overwhelmed by other forces is a different issue.

Our next step, then, is to calculate the maximum force that can be exerted from the various planets, and combine them to get the maximum possible force exerted by the planets.

Show the Math

The force from all the planets combined

All of the forces above were calculated as if the planet is in its closest position to the Earth. The chances that all planets together will be in such positions are incredibly small. This doesn’t usually happen, and the resultant combined force is much smaller. However, we can still calculate the maximum theoretical force that can be produced by all planets combined on the newborn baby.

Here they are:

• Mercury =
• Venus =
• Mars =
• Jupiter =
• Saturn =
• Uranus =
• Neptune =
• Pluto =

(Before you protest about Pluto, read this: there are many problems with including Pluto in the calculation of gravity – the least of which is his “partner” Charon, who’s of similar mass. However, Astrologers calculate Pluto into their maps, and so I thought it would be appropriate to include the force it exerts, too.)

Show the Math

Total Force =

Comparison

So, what do we have?

• The combined forces of the delivery room =
• The combined forces of the planets =

Difference =

The forces from the delivery room are 8 times bigger than the combined force from the planets, and we have calculated a very conservative estimate.

Proponents of the claim might jump out of their seats and claim the forces are extremely close. They seem close (if a factor of 8 is considered close) but we have to remember a few important issues that show conclusively that the forces from the planets are minuscule compared to the forces exerted on the baby from his immediate surroundings:

• The planets do not, ever, line up where they are all as close to Earth as our calculation asserted. The realistic force from the planets is lower.
• Our estimates for both the distances, the amount of people and their weight was very conservative. In reality, hospitals have a lot more people and staff, much more equipment in the room and directly outside of it.
• Hospitals are huge places. If planets as far as a few billion kilometers exert force on our newborn baby, the MRI machine (that weighs 50-60 times the weight of the doctor, nurse and OB Technician combined) at some floor below, and the CT machines somewhere in the hospital should be taken into account as well. Those would dramatically increase the difference between the two forces.
• And, one of the most notable point of all: We ignored the Earth’s gravity!

We ignored the Earth’s gravity!

To be fair, I ignored the Earth’s gravity in both cases, for a very good reason: it absolutely trumps both. Since it is also coming from the ground, and the other forces are spatially distributed, my goal was to show that even without gravity, the difference exists, and is indeed noticeable.

But the Earth’s gravity is important here.

The Earth isn’t a perfect sphere; its radius varies from 6357 km to around 6378 km.

Assume the baby is 6360 km from the center of the Earth.

Show the Math

In this case, the force exerted on him by gravity would be

As you can see, this is times more than the forces exerted by the occupants of the delivery room, and times more than the force exerted by the planets together. It’s a powerful force, gravity.

And there’s more. The Earth’s gravity isn’t constant. It varies across the surface of the planet (as the radius varies). We usually use the average rounded number for the gravitational acceleration () but in different locations on the Earth, the number varies.

If the claim astrologers make is that the force from other planets affect a baby’s personality – and we’ve seen how small that force is! – then the change in the Earth’s gravitation should have an effect too. In this case, Astrologers should consider the location and elevation of your birth as well as the date and time, to calculate the variations in the Earth’s gravity.

The next time an Astrologer offers to calculate your chart, you should reminder them about that.

One more thing: The Labor Itself

We didn’t include this part in the initial calculation, but this is definitely something that we should take into account, since this is likely to be quite a powerful force.

A baby doesn’t just “walk out” of the womb, it is pushed out by the mother’s muscles. If you see any TV shows at all, you know that at the moment where the baby – and doctor – are ready, the doctor will ask the woman to “Push!!” resulting in the baby’s head being pushed out (if all is well) and the doctor assisting the baby the rest of the way.

This “push” and the movement out of the woman’s womb also exert force on the baby. On top of that, there is usually a large amount of time during which the woman’s body exerts force on the baby before it actually comes out. This would apply pressure on his body; obviously, it’s not enough to harm the baby, but it definitely exists. And labors can be long… long and tedious processes. Ask your mother how long she was in labor.

So for a large number of hours (36 is the average!) the baby is subjected to pressure from the mother’s contractions, and then to the force that pushes him or her out of the womb.

So.. why don’t Astrologers ask how long your labor lasted?

Conclusion

There are many things that are plain false in the claims that Astrologers make, and many blogs and sites covered the reasons why. Now, though, you could see for yourselves how the basic premise – that planets’ positions, affect the personality trait of a newborn baby – is just silly.

If the planets’ positions affect the baby’s personality traits, so should the Doctor’s position, the OB Technician, the position of the heart monitor, the CT machine down the hall and the size of the hospital and the amount of people in it.

So, unless Astrologers are willing to take these components into account when they produce your “Chart”, it seems their claims are plain silly.

And you should tell them that.

Do you have more objects to test?

Now you can. Due to popular demand, I’ve prepared a small tool to help you calculate the force from object at any distance. Play with it, and share your findings in the comments!

Click here to open the Force Calculator!

(opens in a new window).

Resources

• http://pregnancy.about.com/cs/laborbasics/a/aa021504a.htm
• Labor and Delivery Room (scribd): http://www.scribd.com/doc/6390726/Labor-and-Delivery-Room
• Monty Python’s Hospital Sketch http://www.youtube.com/watch?v=arCITMfxvEc
• Average fetal weight: http://www.babycenter.com/average-fetal-length-weight-chart
• http://nssdc.gsfc.nasa.gov/planetary/factsheet/
• http://www.universetoday.com/guide-to-space/venus/venus-distance-from-earth/
• http://www.universetoday.com/guide-to-space/mars/distance-from-earth-to-mars/
• http://www.universetoday.com/guide-to-space/jupiter/how-far-is-jupiter-from-earth/
• http://www.universetoday.com/guide-to-space/saturn/saturn-distance-from-earth/
• http://www.universetoday.com/guide-to-space/uranus/uranus-distance-from-earth/
• http://www.universetoday.com/guide-to-space/neptune/how-far-is-neptune-from-earth/
• http://www.spinlife.com/Drive-Medical-600-lbs.-Bariatric-Full-Electric-Frame/spec.cfm?productID=82578
• Stages of Labor: http://www.accd.edu/sac/nursing/rnsg2261/PDFWH/StagesOfLabor.pdf

Thanks

Once again, thanks goes to:

• Capn_Refsmmat, for some language issues, for his mastery of the LaTeX plugin and for his math peer-review.
• Daniel Grrrrrr for his English support and patience. Lots of it.
• UnintentionalChaos (from ScienceForums.net) for some math peer-review and clarity correction issues.

If you’ve been reading this blog and any other astronomy or physics-related article sites, you know the truth about Astrology: the force exerted by the planets in our solar system is smaller than that produced by your furniture, by your neighbors, by orbiting satellites and by skyscrapers in the city nearby.

If that force truly affects your mood or character, then you should be going totally berserk every time your computer reboots, or when you sit in the movies among a few dozen people. Their mass affects you much more than remote planets, that’s for sure.

I’ve been planning to write a full blown analysis of astrology for SmarterThanThat with some actual calculations (because I know how much you all like calculations!) but the subject was discussed ad nauseam all over the net already. A SmarterThanThat analysis (and, possibly, an experiment) will come in the near future, but for now, if you wish to learn more about astrology and its premises, here’s a good place to start.

But apparently, people like believing in astrology - it’s vague assessments are comforting. And it can be fun, in a useless kinda way.

But if you’re still under the impression that astrology has some merit to it, maybe you should watch this video where Richard Saunders (Australian Skeptics, Skeptic Zone podcast, and more) brings the astrologer back to Earth and away from fantasy. Far away. Welcome to reality, Astrology.

www.youtube.com/watch?v=q-fjymxOrGE

I wonder if the astrologer would take on Richard’s invitation. That would make for an interesting (though, I suspect, quite predictable) experiment. I have a feeling that Richard would keep us all updated if this happens.

Don’t hold your breath.

Here it was again this year, The Amazing Meeting 7 in Las Vegas, organized by the James Randi Educational Foundations (JREF). As you may remember from last year’s updates, TAM is usually awesome and this year was no exception.

I met so many cool people, made new friends and greeted some old friends again. I had a great time seeing Phil Plait, the Bad Astronomer (and president of the JREF) again (see picture above), schmoozed with Jamie from “The Cuter Side of Politics” (picture below, with Richard Saunders), watching the very talented Sarah Trachtenberg do her stand-up routine at the TAM Talent Show, and got to do an awesome audio recording with Richard Saunders from the Skeptic Zone that included beer, Australians and sound. Awesome!

The Think Tank Experiment

I had the great privilege to sit down with Richard Saunders, Brian Dunning (from the awesome skeptoid.com) Amanda Rose,  and others to record a special edition of the Skeptic Zone’s Think Tank at the sports bar in the hotel. We sat down with some beers and had a great time sharing a nice little demonstration about the different sounds you can make with half-filled beer bottles.

You are encouraged to listen to the entire episode, where Richard updates from The Amazing Meeting with some interviews and snippets from the different speakers, but if you want to jump straight off to the Think Tank experiment, it starts about an hour and fifteen minutes (1:15) into the show.

The different sounds bottles make

Richard drank all the liquid in his bottle, while I drank only a little bit. Mine was almost full, while his was almost empty. Tapping both bottles produced different sounds; the empty bottle produced higher pitched sound and the full one produced lower pitched sound.

However, when we blew air inside the bottles, the sounds were reversed. The empty bottle produced a low pitch sound and the full bottle produced a high pitch sound (You can see us in action in this great picture).

Why does that happen?

Tapping the bottle causes the glass to vibrate. When the bottle is empty, the glass moves more freely and produces faster vibrations (and higher pitched sound). When it’s full, the liquid prevents the glass from moving as much and the vibrations are slower (and lower pitched sound).

Blowing air into the bottle makes the air itself move around in the space inside the bottle. The sound is produced as the air molecules vibrate at the  bottle’s mouth . When the bottle is empty there’s more room inside for air to move around, and it escapes more slowly. When there’s liquid inside the bottle there’s less room for the air to move around, and it escapes more quickly. The quicker the air escapes the bottle’s opening, the faster the air molecules vibrate and create the sound.

Slow vibrations produce low pitch sound and high vibrations produce high pitch sound. This is one demonstration you can do anywhere where they serve drinks. Bottoms up!

The Awesomeness of TAM

I had a wonderful time in Las Vegas at The Amazing Meeting 7, and I just can’t wait for next year’s Amazing Meeting 8. Are you coming? You should, and if you end up there, walk around, make new friends, and hunt me down to say hello. It’s the best time of year!

Update: You can find more pictures of the great experiment with Richard Saunders at TAM7, in sc00ter’s TAM7 flickr album.

I love “The Biggest Loser“, I watch it weekly and although I am not really doing all their workouts, watching these men and women train hard and transform their lives inspires me to get my buttocks off my computer chair and move myself to the gym too. It’s a great show, really.

The “losing weight” trend is one of the better outcomes of reality TV, and it encourages people to take charge of their lives and live a healthier life.

www.youtube.com/watch?v=0ILYAG4JM30

But there’s one thing that bugs me about this trend: The terminology.

Folks, you lose weight every time you go down a fast elevator. What you actually want is to lose mass. Since your weight is affected by your mass, it will mean that your body will weigh less on the scales the less massive it is, but the goal is not your weight, the goal is your mass.

“Burning fat” and getting rid of excess calories along with training in the gym will make you leaner, thinner, and less massive.

The force that a leaner body exerts on the floor is less than the force a big body exerts on the floor, but what you work on when you want to “lose weight” is, in fact, shaping your body’s mass: losing the mass of fat and/or gaining the mass of muscle.

I can lose weight without touching my mass by simulating a “weightlessness” situation, or by getting close to it.

For example, try riding up and down an elevator while standing on a scale.

When the elevator accelerates downwards, it is moving away from your feet and your body is, essentially, in a condition of “falling”. That decreases the force it exerts on the floor, and you experience a state of semi-weightlessness, depending how strong the elevator’s acceleration is.

When the elevator accelerates upwards, the force your body exerts on the floor is now increassed, because the floor goes up faster than your body can chase it, and your feet are pushed down towards the floor.

Congratulations, you just gained and lost weight in a few minutes.

If you want to be lighter, jump off a plane (with a parachute, please). The state of a ‘free fall‘ your body will be in for the first moments will simulate weightlessness. In these situations your weight is zero, but your mass - the particles that make you “you” didn’t go anywhere.

And though you just lost weight, that does not make you thin.

The term “Weight Loss” is so engrained in our society, that it will be futile of me to try and get you to stop using it. That does not mean, however, that you can’t understand the physics behind those terms.

So, remember: If your goal is to lose weight, ride down an elevator or jump off a plane with a parachute.  If your goal is to be leaner, excercise and eat right, and get rid of that mass of fat that surrounds your muscles.

Alternatively, you can go live on the International Space Station, where weight is not an issue.

Resources and References

• Weightlessness in Wikipedia: http://en.wikipedia.org/wiki/Weightlessness
• “The Biggest Loser” show: http://www.nbc.com/The_Biggest_Loser/

Credits

• Music from http://www.freeplaymusic.com
• “Houston” Mission Control voice: Daniel

Picture Credits (used in the video)

• I heart Nerds T Shirt http://www.flickr.com/photos/elvissa/880588709/
• (Featured photo) Scale http://www.flickr.com/photos/restlessglobetrotter/2929270640/
• Hamburger http://www.flickr.com/photos/jesswebb/2633566137/
• Obese dog http://www.flickr.com/photos/34428760@N03/3202436425/
• Lean dog http://www.flickr.com/photos/draplin/912213752/
• Pyramid http://www.flickr.com/photos/swamibu/2223726960/
• Sky scraper http://www.flickr.com/photos/nogood/220232524/
• Jumping off the roof http://www.flickr.com/photos/paulbence/93988862/
• Elevator free fall http://www.flickr.com/photos/bass_nroll/2215862793/
• Rollercoaster http://www.flickr.com/photos/mprinke/1139986131/
• Gym http://www.flickr.com/photos/abraj/181196330/
• Veggies http://www.flickr.com/photos/valjk/634696442/
• Obesity http://www.flickr.com/photos/combinedmedia/3067501298/
• Iron man http://www.flickr.com/photos/sscusp/242103879/
• Big man with coke http://www.flickr.com/photos/fatmandy/165144643/
• Weight loss http://www.flickr.com/photos/vernonwhite/3327754571/
• Baby cringe http://www.flickr.com/photos/craigforsyth/2384364393/
• Skydiving http://www.flickr.com/photos/gogap/423485388/
• Leaner http://www.flickr.com/photos/christinielsen/97438813/
• Exercise http://www.flickr.com/photos/n8kowald/1467191600/

If you’ve been following my skeptical adventures, you know I have attended the Amazing Meeting 6 (organized by the James Randi Educational Foundation) about a month ago in Las Vegas. Not only have I had a blast and met lots of wonderful people, but I also had the privilege of doing a LIVE experiment with none other than Australian Skeptic’s Richard Saunders.

This was an awesome experiment in an already awesome convention. Don’t forget to check out the JREF website for the DVDs and extras from TAM6. Richard Saunders’ many projects can be checked out through the Australian Skeptics website and the Tank Podcast.

What’s Going On?

When you convert a 3-dimensional object (a face, for example) into a 2-dimentional surface (a page, for example), your end result is stretched and distorted. The reason lies in the curvature of the 3-d object you are trying to copy: The curvatures that give your face the shape it has (your nose, your mouth, your ears), will appear longer when stretched to a flat surface.

What is the Shroud of Turin?

The shroud of Turin is a piece of linen that seems to bear an image of a man lying with his hands in his lap. Some religious groups claim that the image is, in fact, the image of Jesus after his crucifixion.

Whether or not this shroud is real (Scientific examination of the fabric and impressions on it show it is dated much after it is supposed to exist to be authentic), the image that is transcribed on it is interesting. Missing the impression of the face on it is quite hard, and explaining it away with ‘simple’ paraedolia doesn’t seem to do it justice.

But if we take our experiment to mind, this image seems to get a different perspective – literally. Take a look at the above drawing, for example, (by Giulio Clovio), depicting Jesus being wrapped in a shroud after his crucifixion. If, truly, this cloth covered the face and body of a man (any man, for that matter), then the impression should not have appeared as a face at all, it should have appeared distorted. A relatively simple test – print out the image, then fold it in half along the nose line – casts some doubt by itself on the existence of a human model for this image.

How are flat maps made?

The creation of a flat map is similar, but not exactly the same as what you have seen in the video. Since distorted maps are quite useless, the drawing of a flat map uses a technique called “Map Projection”. Essentially, the glove is divided into equal squares which are also drawn on a flat surface map. Each square is copied in exact details to the corresponding square in the flat map.

There are several types of such projections, depending on the type of map you need.

An “Equidistant” projection creates a map that has equal distances from the center (equator). A “Zenithal” projection is one that maintains accurate directions.

In general, a flat map is not the accurate depiction of the way our planet looks. It can’t be, because our planet is spherical. But a map projection, at least, makes the conversion slightly more accurate, and easier for our brain to calculate distances and shapes.

More information about the creation of flat maps out of the curvature of our planet can be found in this website (also on the ‘extra resources’ section at the bottom of this page).

Thanks (Original Idea Credit)

Thanks to Edtharan from ScienceForums.net for this idea!

Extra Resources

• JREF Website (James Randi Educational Foundation): http://www.randi.org/
• Australian Skeptics: http://www.skeptics.com.au/
• The Tank Vodcast: http://tankvodcast.wordpress.com/
• The Shroud of Turin: http://www.shroud.com/ and http://en.wikipedia.org/wiki/Shroud_of_Turin
• How maps are formed (3D to 2D): http://www.nationalatlas.gov/articles/mapping/a_projections.html

Water is dense. Alcohol is Dense. But they’re not the same density, no siree. They’re differently densed. Which means we can use that to our advantage. And we do, in this experiment.

Well, this is more of a “Show off your geektitude” physics trick that will amaze and enchant your buddies anywhere! Okay, well, maybe not anywhere. Or anyone. But it is geeky, I promise. And will get you some attention.

And it’s cool.

And it’s useful. For parties.

I can switch the contents of two glasses without using a third glass. Yes, I can. Don’t believe me? Well – When in doubt, try it out!

So. Anyone who asks a bartender for anything “on the rocks” knows that alcohol and water do not mix. Not properly, anyways. Not without insistent help. The alcohol always ends up floating on top of the excess water that melted off of the ice. But why?

Well, that has to do with the density of both liquids. Dense materials sink, and less-dense materials float. Water is denser than alcohol, so the alcohol floats on top of the water.

Density also changes with temperature. Water is denser when it’s cold. In higher temperature, the density is lower. Hotter water will always “want” to rise up above colder water. And we’re using this property in this nifty trick. Did I say it was cool?

What is Density?

Density is the measurement of mass per unit of volume. Put simply, it is the amount of particles within a specific space in the material used. A bar of gold will have a lot of particles within 1cm cube volume, while water fume will have very few in the same space. So gold is denser than fume. Which is why we choose to wear it as jewelry.

In physics, the general formula is represented by p=m/v, which means that density is mass per volume. If you know the mass and you know the volume (both quite easy to figure out), you can find the density of objects. This is another cool experiment that will be coming up in the future, and you can try it out yourselves with anything, really, as long as you know its volume (size) and weight (and can figure out the mass). Just be careful who you ask..

Why leave a small hole between the cups?

We don’t want our two liquids to mix, we want them to “switch”. When you leave a tiny hole between both cups, a stream of liquid from the bottom cup is flowing upwards, because it’s lighter, and is replaced by a stream of liquid from the top cup (the ‘heavier’ liquid). If we completely discard of our separator, the liquids will simply mix, and we will have diluted alcohol. Or room-temperature water.

When the process is allowed to happen slowly, after a few minutes, both cups are completely filled with the opposite liquids.

Maaaaaagic! Well, no. Physics.

I mean… Phyyyyyyyyyyyyyyyyyysics!

Materials needed for the Experiment

• Two cups of the same size.
• Alcohol
• Water.
• Credit Card / MTA Card / Cardboard.

Don’t drink and drive.
We will go over momentum in future experiments, but this is one thing you all should know.

Practical Applications

You mean other than being the star of a party? Oh, okay okay, here are a few practical applications for knowing the density and buoyancy of liquids:

• Buoyancy! The density of liquids affect their buoyancy. The lowest dry point on earth, for example, the Dead Sea, has a very high salinity, which makes its density a lot higher than regular ocean water. As a result, people (and other objects) float. Without trying.
• Distant Stars: Astronomers can calculate the density of stars from their mass and volume, and understand better about the process that is “running” the star.

Resources

• Water Density: http://www.4physics.com/phy_demo/Galileo_thermometer/galileo-thermometer-d.html
• Water’s Density and the Relation to Temperature: http://www.simetric.co.uk/si_water.htm
• Oil floats on Water: http://www.physlink.com/Education/AskExperts/ae105.cfm