Contact forces are those forces that cause a change in another object because the objects are physically touching one another, according to Reference.com. Examples of contact forces include applied force, tension force, air resistance force and normal force.
In order for force to exist, interaction between two objects must take place. The interaction is sometimes as simple as one object sitting upon a surface. This is a type of contact force because the two objects are touching, and the surface exerts force on the object to support its weight. Contact force is one of the two general categories into which forces between two objects are defined. The other is force from a distance. Examples of this type of force are magnetic and gravitational.