Which of the following is considered a contact forces?1) the force between two magnets. 2) the gravitational pull of a planet. 3) friction between an object and air. 4) the force between two charged particles.

The force between two magnets, the gravitational forces between two objects,

and the forces between two charged particles DON't require that the objects

be touching each other.

The forces of friction between an object and air, or the forces of friction

between two objects that are sliding, DO only happen when the two are

in contact with each other.