Lenz’s Law Tubes

This demonstration shows Lenz’s Law using two similar cylinders, one magnetic and one non-magnetic, dropped through an aluminum tube. The magnetic cylinder falls much more slowly because eddy currents induced in the aluminum create a magnetic field opposing its motion.

1. Secure a long aluminum tube vertically using a rod and stand, or hold it over a padded surface such as sandbags.
2. Drop the non-magnetic aluminum cylinder into the tube and observe that it falls quickly.
3. Drop the magnetic cylinder into the tube and note that it descends slowly compared to the non-magnetic one.
4. (Optional) Use two identical aluminum tubes side by side to “race” the magnetic and non-magnetic cylinders for a dramatic comparison.

Lenz's Law Demonstration - Penn Physics:

Demonstration of Lenz's Law - Grand Illusions:

📄 Lenz’s Law – Wonder Tubes - UCSC Physics Demonstration Room: https://ucscphysicsdemo.sites.ucsc.edu/physics-5c6c-demos/lenzs-law-wonder-tubes/

• Try tubes with different wall thicknesses to see how the effect changes.
• Use magnets of different strengths to compare the falling times.
• Experiment with tubes made of different conductive but non-magnetic metals, such as copper.

• Place sandbags or another soft surface under the tube to prevent cracking or chipping of the magnet when it lands.
• Do not use iron tubes, as they interfere with the effect by strongly attracting the magnet.
• Handle strong magnets with care; they can pinch skin or damage electronic devices.

• Why does the magnetic cylinder fall more slowly than the non-magnetic one? (Because eddy currents induced in the aluminum oppose the motion of the magnet according to Lenz’s Law.)
• What factors influence how much the magnet slows down? (Magnet strength, tube conductivity, and wall thickness.)
• Why doesn’t the non-magnetic cylinder slow down? (No changing magnetic field is produced, so no eddy currents or opposing forces arise.)
• How does this demonstration relate to real-world applications? (Eddy currents are used in magnetic braking systems, induction heating, and metal detectors.)