A force is a push or pull upon an object resulting from the object’s interaction with another object. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction.
Forces (interactions) between objects can be placed into two broad categories:
- contact forces
- forces resulting from action-at-a-distance
Contact forces are forces that result when the two interacting objects are physically contacting each other. Examples of contact forces include frictional forces, air resistance forces, and applied forces.
Action-at-a-distance forces are forces that result even when the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical separation. Examples of action-at-a-distance forces include gravitational forces. Even when your feet leave the earth and you are no longer in physical contact with the earth, there is a gravitational pull between you and the Earth.
Try these simulations to understand more about forces.