B Lenz's law questions from a dad of a smart son

[OmCheeto]

but if i get him a 3/4 inch magnet ball

You'll want to purchase a cylindrical magnet, or a stack of cylindrical magnets, such that their length is greater than the diameter of the tube. The magnetic field generated in the tube is opposite to that of the falling magnet, and will cause the magnet to flip on its way down.

i did find some pipe i could afford like in the 20 30 dollar range

I just did the experiment with a full roll of aluminum foil, and magnets I have around the house.
Total cost: $0.00

It didn't work quite as well as the magnets down my copper pipe.*
But my copper pipe has a smaller diameter than my roll of aluminum foil, and I concluded that for really impressive results, you want to keep the diameter of the magnet as close to the diameter of the tube as possible. Without it getting stuck on the way down, of course.

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*This last summer, the water bureau was fixing my neighbors water pipes at the meter, and I went to investigate. One of the 14 supervisors had a healthy length of copper tubing in his hand, so I ran back home, grabbed my magnets, ran back, showed him your science experiment, and he gave me the tube in appreciation. Yippie!

 

[Keith_McClary]

fixing my neighbors water pipes at the meter...a healthy length of copper tubing

I think the flexible copper pipe for underground use is pure copper and has better conductivity than the rigid indoor pipe, which is an alloy.

I found some discarded hollow aluminum deck railings and a heavy aluminum grill for a portable gas stove,

both of which slow down magnets impressively.

If you know the physics of "how stuff works" you can find interesting materials free or cheap. For example, magnets in hard drives, speakers, microwaves and vibrating toothbrushes.

I can't think of where you would find thick copper or aluminum tubes.