# Why does a magnet do work on a flying nail?

• alyssmainwrg
In summary, the magnetic field will not work on a charged particle that is moving, but when a nail flying over a permanent magnet is attracted by the magnet, the magnet does work on the nail. Can anybody explain why this is so?
alyssmainwrg
When a charged particle moves in a magnetic field, the magnetic field will not work. But when a nail flying over a permanent magnet is attracted by the magnet, the magnet does work on the nail. Can anybody explain why this is so?

Keith_McClary
It is the forces that hold the nail together that do the work. In order to attract the nail there must be a gradient in the field ( a pole face of the magnet). The moving charges in the nail will be feel different magnetic forces and the constraining forces will do work to maintain the nail's integrity. If the nail were loose charges they would dissociate.

vanhees71 and DaveE
alyssmainwrg said:
When a charged particle moves in a magnetic field, the magnetic field will not work. But when a nail flying over a permanent magnet is attracted by the magnet, the magnet does work on the nail. Can anybody explain why this is so?
There is pressure (think "suction") applied to a high-## \mu ## object like a nail in and by a magnetic field situated in a low-## \mu ## region. This pressure is equal to the magnetic energy density everywhere along the nail, and is everywhere normal to the surface of the nail if ## \mu_{air} << \mu_{magnet }##, and is directed towards the region of higher B. So since the B field is stronger closer to the magnet the net suction, ergo force, is in a direction to accelerate the nail towards the magnet.

By conservation of energy, the increase in the nail's kinetic energy equals the reduction of the magnetic field's energy as the distance, ergo volume, of the mag field is reduced as the nail moves towards the magnet.

A stationary charge does not see a force applied to it since its permeability is low. There are probably better explanations in quantum mechanics. In any case a charged particle does not see a force applied to it unless it's moving, and even then the force is orthogonal to the direction of motion so ## dW = \bf F \cdot \bf ds =0 ##.

PS - sorry, laTex seemingly not working.

## 1. Why does a magnet attract a flying nail?

A magnet attracts a flying nail because of its magnetic field. The magnetic field of a magnet exerts a force on the iron atoms in the nail, causing it to move towards the magnet.

## 2. How does a magnet do work on a flying nail?

A magnet does work on a flying nail by exerting a force on the nail, causing it to move towards the magnet. This movement is considered work because it involves the transfer of energy from the magnet to the nail.

## 3. What type of energy is involved in a magnet doing work on a flying nail?

The energy involved in a magnet doing work on a flying nail is magnetic potential energy. This is the energy stored in the magnetic field of the magnet that is used to attract and do work on the nail.

## 4. Can a magnet do work on any material or only on iron objects like a nail?

A magnet can do work on any material that is affected by its magnetic field. However, the strength of the magnetic field and the material's magnetic properties will determine the amount of work that can be done. Iron objects, like a nail, are particularly affected by magnets due to their high magnetic susceptibility.

## 5. Why does a magnet lose its ability to do work on a flying nail over time?

A magnet loses its ability to do work on a flying nail over time due to demagnetization. This is when the magnetic domains in the magnet become disordered, reducing the strength of its magnetic field. This can happen naturally over time or through exposure to external factors such as heat or strong magnetic fields.

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