A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force.
Forces only exist as a result of an interaction.
Examples of contact forces include frictional forces, tensional forces, normal forces, air resistance forces, and applied forces. These specific forces will be discussed in more detail later in Lesson 2 as well as in other lessons. These specific forces will be discussed in more detail later in Lesson 2 as well as in other lessons. As learned in an earlier unit , a vector quantity is a quantity which has both magnitude and direction. Because a force is a vector which has a direction, it is common to represent forces using diagrams in which a force is represented by an arrow.