# Newton's Laws of Motion

1. Aug 4, 2008

### Dschumanji

It is clear that Newton's first two laws of motion deal with motion: the velocity of a moving body is persistant, and net forces cause acceleration of such a body. However, in my opinion, the third law has more to do with the nature of forces rather than motion. The main point is that forces come in pairs of equal magnitude but opposite direction.

Newton's third law of motion should be considered a law of forces, such as the superposition of forces is a law of forces.

Any thoughts on this idea? Am I just being crazy?

2. Aug 5, 2008

### Defennder

Well a force is often associated with motion isn't it? The problem with considering it as a matter of force alone, is that it seems rather disconnected; if body A exerts force F on body B it itself experiences F in an opposite direction. You can't talk about forces alone without considering the bodies and their subsequent motion induced by the forces. Which is why a more accurate statement of Newton's third law makes references to bodies and not just forces.

3. Aug 5, 2008

### Dschumanji

So why isn't the superposition of forces itself considered a law of motion?

4. Aug 5, 2008

### Defennder

I thought that was covered in Newton's 1st and 2nd law, which makes references to a "net" force.

5. Aug 6, 2008

### Dschumanji

It makes use of the principle but is not covered in the first or second law.

6. Aug 6, 2008

### Defennder

It is given in the statement of the first two laws. The laws use the word "net" which is essentially the superposition principle.