Answer
Eddy currents slow the sheet’s movement through the magnetic field.
Work Step by Step
This proposal depends on eddy current braking. As discussed in section 20-6 on page 600, the external magnetic field (from the permanent magnet) interacts with the mobile conduction electrons in the moving aluminum sheet to cause a braking effect.
See figure 21–20. As the aluminum sheet is pulled out of the magnetic field, eddy currents are created in the sheet. The magnetic force on these induced currents opposes the original motion that caused the eddy currents. Thus a resistive force is felt when one is pulling the sheet out from between the poles of the magnet.