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

• Brownian notions
In summary, the conversation is discussing the concept of forces acting on a conducting wire and a magnet. According to Newton's third law, there is a downward force exerted on the wire and an upward force exerted on the magnet. The direction of the reaction force can be determined using concepts such as Fleming's left hand rule for motors. Conservation of momentum and field velocity are not relevant in this static situation.
Brownian notions

## 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!

#### Attachments

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Brownian notions said:
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.

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

Brownian notions said:
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
Brownian notions said:
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.

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

I agree.

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

CWatters said:
I agree.

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

## 1. How does Newton's 3rd law apply to objects at rest?

Newton's 3rd law states that for every action, there is an equal and opposite reaction. This means that even objects at rest are subject to this law. For example, if you push against a wall, the wall pushes back on you with an equal force, according to Newton's 3rd law.

## 2. Does Newton's 3rd law only apply to objects in motion?

No, Newton's 3rd law applies to all objects, whether they are in motion or at rest. This law is a fundamental principle of physics that governs the interaction between all objects in the universe.

## 3. How does Newton's 3rd law apply to a rocket launching into space?

When a rocket launches into space, it exerts a force downwards against the ground. According to Newton's 3rd law, the ground exerts an equal and opposite force upwards on the rocket, propelling it into the air.

## 4. Can you give an example of Newton's 3rd law in everyday life?

An example of Newton's 3rd law in everyday life is bouncing on a trampoline. When you jump up, you exert a force down on the trampoline, and the trampoline exerts an equal force back up on you, causing you to bounce.

## 5. How does Newton's 3rd law apply to a car moving on a flat road?

When a car is moving on a flat road, the wheels exert a force backwards on the road, and the road exerts an equal force forwards on the car. This allows the car to move forward, as dictated by Newton's 3rd law.

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