# Lorentz Force reaction?

1. Dec 10, 2003

### F-Z

In classical Lorentz force demonstration, let's say we have 2 permanent magnets generating a magnetic field perpendicular, out from the page and a wire carrying current to the left. Thus we would expect that the Lorentz Force will exert an upward force on the wire.

According to Newton's 3rd law, there should be a reaction to this force. So do the magnets actually being pushed down? Or is there something else to compensate for the momentum?

Thanks.

2. Dec 10, 2003

### turin

There are three objects: the magnet, the wire, and the field. The field mediates the interaction. Nonrelativistically, you can just consider the action reaction at a distance, so the magnet would be pushed with an opposite force. Relativistically, if the wire expreriences an impulse from the field, then the field experiences an opposite impulse from the wire. This impulse is transfered at the speed c to the magnet. If what you meant by "classically" was "nonrelativistically," then you are talking action-at-a-distance, and Newton's third law treats the two objects, magnet and wire, as interacting directly at a distance.

3. Dec 11, 2003