# Anyone know some cool physics demonstrations?

I have to create a demonstration for my physics class which will be delivered to a local elementary school. Has anyone seen anything of particular interest? The major restriction is that this has to be something the kids can interact with in some form. For example, one year a group created a block and tackle tug of war so that a single elementary student could out tug a group of high school students. I had considered building a lifter, but there's no real interaction with these. I've seen some cool stuff on university websites, but it's all either too minuscule to satisfy the project in and of itself or its beyond what I could build or have access to. Suggestions are greatly appreciated.

## Answers and Replies

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sylas
Science Advisor
I have to create a demonstration for my physics class which will be delivered to a local elementary school. Has anyone seen anything of particular interest? The major restriction is that this has to be something the kids can interact with in some form. For example, one year a group created a block and tackle tug of war so that a single elementary student could out tug a group of high school students. I had considered building a lifter, but there's no real interaction with these. I've seen some cool stuff on university websites, but it's all either too minuscule to satisfy the project in and of itself or its beyond what I could build or have access to. Suggestions are greatly appreciated.
Here's a good one I have done, and seen done.

You have to make two handles to fit on a bicycle wheel. When I did it, I welded bike nuts into a small steel pipe, so that they could be screwed on to each side of the wheel. A student can then hold the wheel by the pipes, as handles.

You need to make sure the students are old enough and strong enough to hold the wheel safely. It is a good idea to have them hold the wheel so that it can spin in the normal vertical plane, then spin the wheel fairly slowly, and have them try to turn it over slowly. They will feel the wheel twisting in their hands.

Then, if they are able to hold on to the wheel safely while it spins at higher speeds, have them sit on a revolving chair, and hold the wheel so that it can spin horizontally. Then spin up the wheel as fast as you can get it to go. I've also seen this done using a drill with a small wheel mounted on it, and then have this applied to the rim of the bike wheel to spin it up smoothly.

The, have the student turn the wheel over completely. They can do this as a smooth continuous turn; there's no need to jerk it. They will find they they start to spin around on the chair, as angular momentum is conserved.

It is also possible to tie a rope to just one of the handle, and spin up the wheel. You can hold up the wheel by the rope while it precesses around, like a gyroscope.

I did this just recently at a kids science-themed birthday party; though in that case I omitted the spinning chair trick, as I felt the kids were a bit too young to make it completely safe.

Cheers -- sylas

Thanks for the tip sylas. We actually did this in class early in the year. Its an excellent demonstration, although I'm not sure it would constitute the entire project. I may end up doing several small related demonstrations. Anyway, thanks again for the idea and if anyone else has some advice let me know.

sylas
Science Advisor
Thanks for the tip sylas. We actually did this in class early in the year. Its an excellent demonstration, although I'm not sure it would constitute the entire project. I may end up doing several small related demonstrations. Anyway, thanks again for the idea and if anyone else has some advice let me know.
Here's another one. I built an air-vortex gun for the same party. We used it to blow out the candles.

This basically consists of a large chamber with a circular hole at one end. I used a plastic washtub, and cut a hole about 20 cm across in the bottom.

Then you need a bellows. I fixed plastic sheeting to the top of the tub, and had teh whole thing mounted in a frame made up of an old chair. Then I applied elastic across the sheeting, so that you could pull it back, and release, so that a blast of air is pushed through the hole.

This should form a relatively stable vortex, in the shape of a smoke ring, which will travel a long distance and give a strong blast of air at anyone down range. Great fun. I also hired a smoke generator, so that the rings could be seen, and we could experiment with different strength and speeds in the bellows.

I have some photos in my sister-in-law's computer which I need to extract and exhibit. In the meantime, here is a video of other people who have done the same thing.
https://www.youtube.com/watch?v=lMLop6MIwUU
https://www.youtube.com/watch?v=-VL0M0jmu7k