Lenz's Law Eddy-Current Magnetic Braking Pipe Lab
A challenging, hands-on discovery and STEM project designed for curious young minds aged 10 to 14.
Materials Needed
- • Thick-walled copper plumbing pipe (approx. 1 meter long, 3/4-inch diameter) (1 pipe)
- • Aluminum pipe and PVC plastic pipe of matching length and diameter (2 pipes)
- • Strong cylindrical neodymium magnet (fits loosely inside pipes) (1 unit)
- • Non-magnetic steel slug or marble of matching mass (1 unit)
- • Digital stopwatch and soft landing cushion (1 set)
Pro Tips
- → Copper is non-magnetic, so a magnet doesn't stick to it; but dropping a magnet through a vertical copper pipe produces dramatic slow-motion falling.
- → As the magnet falls, its moving magnetic field induces circular eddy currents in the copper wall.
- → By Lenz’s law, these induced currents create an opposing magnetic field that acts like an invisible brake, floating the magnet downward slowly.
Safety First
Neodymium magnets are strong; keep away from electronics, magnetic media, and credit cards.
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Step-by-Step Instructions
Step 1
Hold a 1-meter plastic PVC pipe vertically over a soft cushion, drop a steel slug, and time its descent with a stopwatch (approx. 0.45 seconds).
Step 2
Drop a strong cylindrical neodymium magnet through the PVC pipe to establish baseline freefall gravity speed.
Step 3
Drop the same neodymium magnet down a 1-meter thick-walled copper pipe: observe it float down in slow motion taking 4 to 6 seconds to exit.
Step 4
Repeat with an aluminum pipe to compare the electrical conductivity and eddy-current braking strength of aluminum versus copper.