Explain the difference between contact forces and non-contact forces. Give an example of each.

Contact forces and non-contact forces are two categories of forces that are fundamental in physics.

1. Contact Forces: As the name suggests, contact forces are those forces that occur when two objects are in physical contact with each other. The force is exerted only when there is a direct interaction between the objects. Examples of contact forces include frictional force, tension force, normal force, air resistance force, and applied force.

   For instance, when you push a stalled car, you are applying a force directly to the car. This is an example of a contact force.

2. Non-Contact Forces: Non-contact forces, on the other hand, are forces that can act at a distance, meaning the objects do not need to be in physical contact with each other for the force to be exerted. These forces can act over a distance because they are caused by fields, such as gravitational fields, electric fields, and magnetic fields. Examples of non-contact forces include gravitational force, electrostatic force, and magnetic force.

   For example, the force that the Earth exerts to pull objects towards its center is a non-contact force known as gravity. Even when the object is in mid-air, with no physical contact with the Earth, it is still subject to this gravitational pull.

In summary, the main difference between contact and non-contact forces is whether or not the objects need to be in physical contact with each other for the force to be exerted.