# How does Newton's 3rd law apply in this case?

## Homework Statement

It is clear that SOMETHING exerts a force on the conducting wire in a downwards direction.
By Newton's 3rd law, the (field of) this conducting wire also exerts a force on something.

## Homework Equations

Could the magnet be said to move upwards (and hence reading decrease) due to an equal opposite reaction force?

## The Attempt at a Solution

I'm not sure which direction the "reaction force" acts in. I've also read a bunch about conservation of momentum and having to consider field velocity, but is there any way to answer this question without talking about all that? Thanks!

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Orodruin
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Could the magnet be said to move upwards (and hence reading decrease)
These are not the same thing. Something can be stationary and still have different forces acting upon it.

I'm not sure which direction the "reaction force" acts in.
What does Newton's third law tell you?

I've also read a bunch about conservation of momentum and having to consider field velocity, but is there any way to answer this question without talking about all that?
This is a static situation. There is no reason whatsoever to involve velocities.

Hmm so would it be conceptually accurate to phrase the problem this way:

Force 1: force of magnet on conductor (downwards)
Force 2: force of conductor on magnet (upwards) ?

CWatters
Orodruin
Staff Emeritus
Homework Helper
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Hmm so would it be conceptually accurate to phrase the problem this way:

Force 1: force of magnet on conductor (downwards)
Force 2: force of conductor on magnet (upwards) ?
Yes.

Yes.
Cool, thank you! Hope you don’t mind if I wait around for a second opinion before marking it as solved!

CWatters
Homework Helper
Gold Member
I agree.

Your working should mention Fleming's left hand rule for motors.

I agree.

Your working should mention Fleming's left hand rule for motors.
Awesome, thank you!