Some common types of forces that you will be dealing with include the gravitational force (weight), the force of tension, the force of friction, and the normal force. It is sometimes convenient to classify forces as either contact forces between two objects that are touching or as long-range forces between two objects that are some distance apart. Contact forces include tension, friction, and the normal force. Long-range forces include gravity and electromagnetic forces. Note that such a distinction is useful but not really fundamental: For instance, on a microscopic scale the force of friction is really an electromagnetic force. In this problem, you will identify the types of forces acting on objects in various situations.

Now consider a different situation. A string is attached to a heavy block and is used to pull the block to the right along a rough horizontal table.

a. What is the upward force that acts on the book called?

1-tension
2-normal force
3-weight
4-friction

b. Which object exerts a force on the block that is directed to the right?

1-the block itself
2-the earth
3-the surface of the table
4-the string

The upward force that acts on the book is called "tension" while the "string" is the object that exerts a force on the block that is directed to the right.

As the string is pulled, the tension exerts an upward force on the block. The frictional force acts on the block to the left. So, both the tension and friction will act on the block in order to effect its pulling on the surface of the table.