Consider a bowling ball (or some other heavy object that moves with little resistance). If you want the ball to move, you have to exert a force on it in the direction you want it to move. If you want the moving ball to turn, you have to exert a force on it toward the side you want it to turn toward. If you want the ball to stop moving, you have to exert a force opposite to its velocity.  To change the motion of the bowling ball, you will probably apply a force by using your hands or feet or some object you push against the ball. There are other kinds of forces, however. The earth, for example, can alter the ball's motion through the invisible action-at-a-distance of [gravity], often represented as a gravitational field acting on the body at the site of the body.

Newton's Laws describe the consequences of forces and give the rules they must obey, but the laws do not explain the types of forces that can be exerted. There are a vast array of ways for objects to interact with each other, but the ways that are commonly treated in introductory physics courses is a rather short list:

1. contact force occur when one object comes in contact with another.
2. [gravitational force] is the attraction at a distance between objects with non zero mass. In introductory physics, we most often consider the force of [gravity], which is the force exerted by the gravitational field of the earth on objects near its surface, in which special case the force is usually called weight.
3. normal force is the component of the contact force applied by a surface on an object that is either at rest on the surface or moving along it. The normal force is always perpendicular to the surface. For example, the surface can be a floor, wall, ceiling, incline plane, or the track of a roller coaster.
4. tension is a force exerted by a string or rope on an object.
5. friction is the component of the contact force applied by a surface on an object that is either at rest or moving along the surface. The friction force is always parallel to surface. If the object is moving along the surface, the direction of the friction force is always opposite to the object's motion. If the object is at rest on the surface, the direction and the magnitude of the friction force is opposite to the sum of the force from the other forces acting on the object such that the net force on the object is zero parallel to the surface.