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Mercredi, 16 Novembre 2011 20:45

Simple Physics Demos

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Simple Physics Demos

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:

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.

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Simple Physics DemosRhett Allain is an Associate Professor of Physics at Southeastern Louisiana University. He enjoys teaching and talking about physics. Sometimes he takes things apart and can't put them back together.
Follow @rjallain on Twitter.

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