Copper Tube
Time: 0.00s
Velocity: 0.0 m/s
Free Fall (No Tube)
Time: 0.00s
Velocity: 0.0 m/s
Distance Fallen Comparison
Copper
0 cm
Free Fall
0 cm
5 (relative)
7 (copper=7)

The Paradox

Drop a magnet through a copper tube. Copper isn't magnetic at all - you can't stick a magnet to it.

Yet the magnet falls in SLOW MOTION, taking 5-10 times longer than normal free fall!

There's no physical contact between the magnet and tube. It's like the magnet is falling through invisible honey!

The Physics: Lenz's Law

  1. Falling magnet creates changing magnetic flux through the tube walls
  2. By Faraday's Law, this induces eddy currents circulating in the copper
  3. These currents create their own magnetic field that opposes the change (Lenz's Law)
  4. The opposing field exerts a drag force on the magnet, slowing it down
EMF = -dΦ/dt
(Induced voltage opposes flux change)

Heinrich Lenz (1834)

Lenz formulated his law: "The direction of induced current is such that it opposes the change that produced it."

This is nature's way of enforcing energy conservation - the magnet's kinetic energy is converted to heat in the copper via the induced currents.

Real Applications

1. Roller coaster brakes - Magnetic braking with no wear
2. Train braking - Eddy current brakes on high-speed trains
3. Metal detectors - Detect conductive materials
4. Induction cooktops - Heat metal pans directly
5. Speedometers - Older car speedometers used this