Newton's Third Law: Solving the Man & Sled Puzzle

[brewAP2010]

Homework Statement

If a man pulls forward on a sled, and the sled pulls backward on the man with an equal amount of force, how can the man and sled move at all?

Homework Equations

The Attempt at a Solution

 

[PhanthomJay]

Since the sled will move, you should think about what Newton's 2nd law says compared to his third law. What are your thoughts?

 

[ehild]

If a man pulls forward on a sled, and the sled pulls backward on the man with an equal amount of force, how can the man and sled move at all?

It is not only man and sled, but there is also the Earth they interact with.

ehild

 

[harp AP 2010]

He manages to move the sled by digging in his feet with more resistance than the sled can muster from its friction with the ground. If it were done on ice, he would not need to apply much force.

 

[rwisz]

This phenomenon can be explained by Newton's Third Law of Motion, which states that for every action, there is an equal and opposite reaction. In this scenario, the man and sled are exerting equal and opposite forces on each other. However, it is important to note that these forces act on different objects and in opposite directions, resulting in a net force of zero on the system (man and sled). This means that the man and sled will not accelerate in any direction, but rather remain in equilibrium. In order for the man and sled to move, an external force must be applied, such as the force of friction between the sled and the ground. This force, in addition to the forces exerted by the man and sled, will result in a net force and cause the system to move. Therefore, the man and sled can move together as a result of the equal and opposite forces acting on them, but only when an external force is present to break the equilibrium.