When a bar magnet is dropped through a vertical length of...

Name: Problem 47, Chapter 11: Conceptual Physics Fundamentals
Uploaded: 2021-10-11T17:10:34-08:00
Duration: 55 s
Channel: Keshav Singh
Description: When a bar magnet is dropped through a vertical length of copper pipe, it falls noticeably more slowly than it does when it is dropped through a vertical length of plastic pipe. If the copper pipe is long enough, the dropped magnet will reach a terminal falling speed. Propose an explanation.

When a bar magnet is dropped through a vertical length of copper pipe, it falls noticeably more slowly than it does when it is dropped through a vertical length of plastic pipe. If the copper pipe is long enough, the dropped magnet will reach a terminal falling speed. Propose an explanation.

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Key Concepts

Electromagnetic Induction

This is the process whereby a changing magnetic field produces an electric current in a conductor. When the magnet falls through the copper pipe, the movement of its magnetic field relative to the conductor induces currents in the pipe walls, illustrating this fundamental phenomenon of electromagnetism.

Lenz's Law

Lenz's law states that the direction of the induced current is such that it opposes the change in the magnetic field that created it. In the scenario of the falling magnet, this means that the induced currents in the copper pipe generate their own magnetic field which opposes the motion of the magnet, slowing its fall.

Eddy Currents

These are loops of electrical current induced within conductors by a changing magnetic field in the conductor, due to electromagnetic induction. In the case of the falling bar magnet, eddy currents in the copper pipe produce a magnetic field that counteracts the magnet’s motion, creating a resistive force.

Terminal Velocity

Terminal velocity is the constant speed that an object eventually reaches when the force of gravity is balanced by a drag force. In this situation, the magnetic drag caused by the induced eddy currents balances the gravitational force, leading to a constant falling speed for the magnet in a long copper pipe.

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