Simply drop a neodymium magnet down a copper tube.
This should make it obvious that - Gravity is Optional.
When questioned about why the magnet seems to float down the tube, simply explain that the metal was discovered at the Roswell crash site, and that NASA uses this anti-gravity metal in all the current space craft.
Most of that is actually true. Copper wires are used in all cars, jeeps, and space craft. Sure, it is used to carry electricity and not for its (obvious) "anti-gravity" properties, but it is there.
Or you could simply explain the physics.
Once you have the magnets, go to the local hardware store and buy a 2' piece of copper water pipe. To get the correct size, stick the magnets together (to make a stack of 4) and find the smallest pipe they will fall through. It is important to stick at least 4 magnets together - otherwise, they will twist and get stuck in the pipe.
Copper tubing is available in four wall thicknesses:
|Type||Relative wall thickness||Usage (from Wikipedia)|
|DWV||Thinnest||Only allowed as drain pipe per UPC|
|M||Thin||Typically only allowed as drain pipe by IPC code|
|L||Thicker||Standard duty for water lines and water service|
|K||Thickest||Typically used underground between the main and the meter|
Terminology is a little weird at first
Since the tube size refers to the outside diameter, 1/2" L copper has the same outer diameter as 1/2" K or M copper. Since a thicker pipe places the metal closer to the magnets, they should fall slower. Since there is more metal around the magnets, they will fall slower.
One of the emails I recieved suggested that standard 5/8" tubing has the same size as 1/2" pipe (1/16" wall). However, ASTM B88 indicates that 5/8" copper tube has an outside diameter of 3/4" which, with the same 1/16" wall, would have an inside diameter of 5/8". As a result, I am not sure what is going on. Of course, I have (incorrectly) used both terms for the same item. Perhaps this table will help.
|From Copper Tubes - ASTM B88|
|Actual Outside Diameter|