Gravity is Optional - EddyCurrents - Copper and Aluminum Tubes

Gravity is Optional - EddyCurrents
Copper and Aluminum Tubes

Everyone knows that copper and aluminum are not attracted to a magnet. We are taught that at an early age. These experiments use magnets with copper and aluminum tubes.

The Experiment | Obtaining materials

The Experiment

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.

Obtaining materials

This is easy to reproduce at home. In 2012, four 1/2" neodymium magnets on a card were between $2 and $4 in many craft stores. (In the Washington , DC area, both Michaels and Walmart carried them, but not on their web pages.) Only the more expensive silver colored magnets worked, the black ones are not strong enough. As of 2012, the local stores only carry smaller 1/4" magnets, the 1/2" magnets are no longer available. However, they are still easy to get via the internet - 40 for about $12.

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

The thicker the pipe, the higher the cost. Thicker walled pipe generally implies greater durability, higher pressure tolerances, and slower magnets.

Terminology is a little weird at first

Pipe is sized by the inside diameter which is related to the amount of fluid that flows through it.
Tubing is sized by the outside diameter which allows standard fittings to be used.

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
Type	Nominal Size (inches)	Actual Outside Diameter (inches)		Wall Thickness (inches)		Weight (lb/ft)
Type	Nominal Size (inches)	Actual Outside Diameter (inches)		Nominal	Tolerance	Weight (lb/ft)
K	1/4	3/8	0.375	0.035	0.0035	0.133
L				0.030	0.003	0.126
M				~	~	0.106
K	1/2	5/8	0.625	0.049	0.005	0.344
L				0.040	0.004	0.285
M				0.028	0.003	0.203
K	1	1 1/8	1.125	0.065	0.006	0.837
L				0.050	0.005	0.655
M				0.035	0.004	0.464

Author: Robert Clemenzi