# Newton's Law

What is Newton's Third Law?
For every action there is an equal and opposite reaction
Original post by hungrysalamander
For every action there is an equal and opposite reaction

This user is correct.

Some people find this confusing, so you could also say, that when body A exerts a force on body B, body B exerts a force equal in magnitude but opposite in direction on body A.

This helps you to understand the fact the forces are exerted on different objects and not the same object, which is why weight and normal reaction force aren’t action-reaction pairs. The forces also have to be of the same type.

GGG
Original post by edwinelberticb
What is Newton's Third Law?

Simply speaking, it means that a force (action) that influence on an object causes a counter force (reaction). In other words: forces on an object work in pairs. They have different directions in which they work, but equal magnitudes.

Example:

A jet is moving thanks to the jet engine that pushes it forwards. The force, which is needed to change the state of motion, is in the jet's direction (action). The jet in turn pushes the engine backwards, so in the counter direction with a counter force (reaction).

Strictly speaking all motions wouldn't work without these forces in pairs, even if it is just walking...
(edited 1 year ago)
Original post by Kallisto
Simply speaking, it means that a force (action) working in a direction causes an opposite force (reaction) in the opposite direction. Both forces have the equal magnitude.

Example:

The motion of a jet in a certain direction (action) is caused by a jet engine working in an opposite direction (reaction). The force for the motion is equal to the opposite force of the jet engine.

Strictly speaking all motions wouldn't work without these forces in pairs, even if it is just walking...

I recommend that you review your example.
You are “explaining” force causes motion and this is wrong!
Original post by Eimmanuel
I recommend that you review your example.
You are “explaining” force causes motion and this is wrong!

Oh, true. Thanks!

the force is just a consequence of motion, Motion itself is caused by acceleration to change the object's state of rest (and of course the velocity of an object in motion). I will correct it!
Original post by Kallisto
Simply speaking, it means that a force (action) that influence on an object causes a counter force (reaction). In other words: forces on an object work in pairs. They have different directions in which they work, but equal magnitudes.

Example:

A jet is moving thanks to the jet engine that pushes it forward. This motion is causing a force in the jet's direction (action). The jet in turn pushes the engine back, so in the counter direction with a counter force (reaction).

Strictly speaking all motions wouldn't work without these forces in pairs, even if it is just walking...

Original post by Kallisto
Oh, true. Thanks!

the force is just a consequence of motion, Motion itself is caused by acceleration to change the object's state of rest (and of course the velocity of an object in motion). I will correct it!

I understand that English is not your native language. If you are directly translating from your native language to English, you may want to consult English references to check what you have written.

We don’t need a force to cause an object to be in motion. If an object is at rest, we need a force to change the state of motion of the object ie to get the object to start to move. If there is no opposing force such as air resistance or friction, the object will move with a constant velocity until some forces act on the moving object to change its state of motion ie to stop the moving object.

Hopefully, you can check your understanding with a good reference.
Original post by Eimmanuel
I understand that English is not your native language. If you are directly translating from your native language to English, you may want to consult English references to check what you have written.

We don’t need a force to cause an object to be in motion. If an object is at rest, we need a force to change the state of motion of the object ie to get the object to start to move. If there is no opposing force such as air resistance or friction, the object will move with a constant velocity until some forces act on the moving object to change its state of motion ie to stop the moving object.

Hopefully, you can check your understanding with a good reference.

Very kind of you that you are so helpful and considerate with me, because English is not my native language. Nonetheless I have question to your explanation: don't we need an acceleration to change the state of motion of an object, but a force for acceleration? So no force, no acceleration and no acceleration, no state of motion to get an object in motion at last?
Original post by Kallisto
Very kind of you that you are so helpful and considerate with me, because English is not my native language. Nonetheless I have question to your explanation: don't we need an acceleration to change the state of motion of an object, but a force for acceleration? So no force, no acceleration and no acceleration, no state of motion to get an object in motion at last?

don't we need an acceleration to change the state of motion of an object, but a force for acceleration?

Indeed, force causes an object to accelerate and force is needed to change the state of motion of an object.

So no force, no acceleration and no acceleration, no state of motion to get an object in motion at last?

Force is needed to cause an object at rest to move. An object that is resting is in a state of motion. An object at rest and an object moving with constant velocity are actually the same state of motion.
It would be better that you phrase your question proper statement to avoid confusion. I don’t know what you mean by no state of motion.

Original post by Kallisto
…the force is just a consequence of motion, Motion itself is caused by acceleration to change the object's state of rest (and of course the velocity of an object in motion).

Be very frank, none of the points is good.
Original post by Eimmanuel
(...) I don’t know what you mean by no state of motion.

Be very frank, none of the points is good.

movement state? if that word exists as term in English any. Okay, tell me in your words what the true points are and put it in a nutshell.
(edited 1 year ago)
I think your “movement state” is state of motion.

In a nutshell, a force causes an object to accelerate (Newton’s 2nd law) OR a force causes an object to change its state of motion.

Read post #7 and #9 a few times.

Original post by Kallisto
the force is just a consequence of motion,

The change of state of motion of an object is the consequence of applying a force on the object.

Original post by Kallisto
Motion itself is caused by acceleration to change the object's state of rest (and of course the velocity of an object in motion). I will correct it!

Not really sure what you want to describe.
Motion is just motion while acceleration is a change in the motion (in short) over a period of a time interval or rate of change of velocity.

If you have further queries, send me an email as I don't want to further "kidnapped the thread". Thanks.