Contact Forces: Contact forces must touch the object that they push or pull, for example, hitting a tennis ball. The racket applies a contact force when hitting the ball. Another common example of a contact force is friction. Friction is a force that opposes the relative motion of an object. If you slide down an icy hill with a toboggan, it slows down and eventually stops because friction resists its motion. But if you slide the same toboggan on a wooden floor, it will slow down faster because the wood creates more friction on the toboggan than the ice does.
Action-at-a-distance Forces: Action-at-a-distance forces can push or pull an object without touching it. Gravity, static electricity, and magnetism all produce action-at-a-distance forces. Another term for action-at-a-distance forces is called non-contact forces. The main non-contact force is the force of gravity. Gravity is the attraction between two different objects due to their mass. The amount of attraction depends upon the amount of each object's mass and the distance between the two objects. For example, when we let go of a ball, the ball is immediately pulled to the ground because of the force of gravity, even though nothing is touching it. This is because the ball and the Earth have mass and therefore are attracted to one another.
Classifying Forces
Contact Forces: Contact forces must touch the object that they push or pull, for example, hitting a tennis ball. The racket applies a contact force when hitting the ball. Another common example of a contact force is friction. Friction is a force that opposes the relative motion of an object. If you slide down an icy hill with a toboggan, it slows down and eventually stops because friction resists its motion. But if you slide the same toboggan on a wooden floor, it will slow down faster because the wood creates more friction on the toboggan than the ice does.
Action-at-a-distance Forces: Action-at-a-distance forces can push or pull an object without touching it. Gravity, static electricity, and magnetism all produce action-at-a-distance forces. Another term for action-at-a-distance forces is called non-contact forces. The main non-contact force is the force of gravity. Gravity is the attraction between two different objects due to their mass. The amount of attraction depends upon the amount of each object's mass and the distance between the two objects. For example, when we let go of a ball, the ball is immediately pulled to the ground because of the force of gravity, even though nothing is touching it. This is because the ball and the Earth have mass and therefore are attracted to one another.
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