1. The copper tube/magnet demo
What was going on there?

2. Important points: The copper tube is non-magnetic
The copper tube is a good conductor
The magnet has a B field
As the magnet drops down the tube, the tube is exposed to a changing B field
This changing B field induces localized currents in the walls of the tube (eddy currents)
The induced I creates a second B field that opposes the magnets B field

3. That is a lot of words – how about a visual
Interaction with one wall of tube wall
Magnet drops down = ΔB I
Induces I (localized)
I results in it’s own B field (B2)

4. Or at least
That is the main idea behind the observed phenomena