User:Shanker Pur/Pull and Push

Pull and Push "A force is a pull or a push" is how the term "force" in physics is often introduced, a pull being distinguished from a push by the direction in which the forces act. A careful analysis may be necessary to determine which of the two - push and pull - is operating in any given situation.

The force of gravity is usually associated with the term 'pull'. Thus the moon stays in orbit around the earth because of the 'pull' of gravity. A ball thrown upwards is brought back down because of the 'pull' of gravity.

Unlike gravity which is always attractive, electric and magnetic interactions can be attractive or repulsive. A magnet may thus 'push' another magnet away. It may 'pull' another magnet towards itself.

A string is a pull mechanism. To 'push on a string' is to do a useless thing.

When a body A exerts a force on a body B, A is the orgin of the force. If the force is towards A, it is called a pull. If the force on B is away from A it is natural to call it a push. But these latter two statements are only true to a first approximation as we see below.

When animate beings are involved in a force interaction, there is typically an initiating agent that is involved in the interaction. Thus Johnny might pull the cat's tail. Although by Newton's 3rd law, the cat pulls Johnny with an equal force, it is Johnny who gets told off by his grandma. The origin of the force is not synonmous with the agent responsible for the interaction.

Johnny might want to move a cup on the table away from him. He can move it away by pushing with his finger on the near side of the cup. Or he may move it away by grabbing hold of the cup on the far side and then pulling it away from him. To move something away is not to push it away.

When a thing is being pulled apart, it is in tension. When it is being pushed in from both ends, it is in compression. Yet when an apple falls towards the earth because of the pull of gravity, it is in a state of weightlessness and there is no tensile stress generated by the force of gravity.

An old chestnut:does a horse push or pull a cart?

External links

• example.com