This past weekend, the Louisiana Section of the AAPT participated in the joint NSTA-AAPT Physics day. The most popular presentation was the “really simple and cheap physics demos”. Lots of participants asked about the demo details. Although I posted a simple list of the demos, I figured it wouldn’t hurt to give slightly more detail. So, here you go. A note about the demos. Why did I choose these particular demos? Really, these fit the following criteria: They are cheap. Cheap in that you could produce these yourself without purchasing too much stuff. You would probably have most of this stuff lying around.

They are relatively easy to perform (at least most of them).

No bulky items. There are some great and cheap and simple demos, but they were too bulky. This demo show was at the convention center in New Orleans. So, if I want something in the show, I had to carry it (or at least cart it) myself.

Nothing needs to be plugged in. Again, I wasn’t too sure about the availability of outlets. I didn’t want to have to bring extension cables so I just decided to not do anything that requires power.

Finally, I tried to pick things that could show something with a simple explanation. You know, stuff most people could understand without a extensive background in physics.

Oh, and one more note (even though the last point said “finally”): just about all of these demos were stolen from other blogs or demo shows that I went to. Above: Climbing wood on stick I can’t remember (or find) the blog where I saw this demo. Basically, it is wooden dowel fit through a hole in a larger block. You hit the dowel with a hammer and the large block appears to rise. How does it work? Basically, this demonstrates the inertia property of matter. The large block takes a force to change its momentum. So, hitting the dowel tends to move the dowel down more than the block. When your hand pulls up on the stick to return it to the starting position, the block ends up higher than it started. Are there any tricks or tips? Well, you don’t want the dowel too tight in the block or it won’t move too well. If it is too lose, it will slide down. So you need to find a compromise. Also, the demo might not work with smaller kids since they have to hold the larger block with one hand. There is a cheat for this case. Put the bottom of the dowel on something squishy – like thick carpet. The block will still rise when you hit it as long as the dowel has a chance to move down on impact. So, this won’t work if you rest the dowel on a hard floor.

Mystery Tube This isn’t a science demo. It is a demo ABOUT science. Also, I have a photo of this demo. Here you go:

What is the color black? This demo is basically a box with a tube in it. Students look in the tube and tell me what color they see on the inside of the box. The point is to show that when they see the color black, it is really what happens when no light enters your eye. Here is an old post that goes over all the details.

Center of mass, friction, and a meter stick This is an oldie…well, its an oldie where I come from. The basic idea is that if you rest the meter stick on two fingers and slide them towards each other, they meet at the center of mass. For added effect, you can put an extra mass on the meter stick so that the center of mass is not the center. Also, as Andrew pointed out (at Drew’s Day’) this is a classic demo. Of course my demo is a bit better than Julius Miller’s version since it is in COLOR.

Balancing a stick on your finger This one might take some practice, but it is totally worth the time you put into it. Also, here is a more detailed explanation why the longer stick is easier to balance.

Power Balance is Fake Demo This is the one demo that I mostly made up myself. Think of it as my contribution to the demo world. In short, it is demo that exposes the Power Balance trick that is used in the commercials and stuff. Here are some Power Balance posts to help things out. Power Balance is losing power

Build your own energy balance thing

Some great posts on the Power Balance

Does the iRenew Frequency bracelet really give you balance …

Accelerometer This is just a floating thing inside a glass container held to the bottom by a string. When the object accelerates, the floater moves in the direction of the acceleration. The best use is to have a student hold it at arms length and spin. The floater will point towards them. Here is a previous post on an even cooler accelerometer that I built. Also, a video from Dale Basler showing his accelerometer inside his car.

Super Simple Potato Launcher This is surprisingly cool. Take a tube and sharpen both ends. Next jam one end into a potato so that the potato remains plugged into that end. Now jam the other end into the potato. At this point, you should have a tube with potatoes stuck in both ends (and air trapped in between). Next take a dowel and push real quick on one potato at the end of the dowel. The other potato piece will end up shooting out. It will help if the dowel has something to protect you from the sharp ends of the tube. For me, I added a block to the end of the dowel. What does this show? First, it shows that the air inside the tube is compressible and can act like a spring. It also shows the difference between kinetic and static friction. Since the static friction coefficient is greater than the kinetic coefficient, you can slide one potato piece before the other piece becomes unstuck. By the time it does slide free, you have stored quite a bit of energy in the compressed air. BOOOM. There goes the potato.

Moroccan Serving Tray (or maybe it is Turkish) How does it work? What does it show? I like to say that it shows that strings only pull in the direction of the string. So if you were a little person inside the cup of water, you would only feel gravity and a fake force in the direction of the string. Here is a more detailed explanation.

Cartesian Diver This shows two things. First, that as you squeeze the bottle the pressure increases and the volume of trapped air decreases. Second, the buoyancy force on the diver depends on the amount of water displaced. With a smaller air volume, there is a smaller buoyancy force.