Forces are responsible for all the interactions between particles and objects. They can be put into two categories: contact forces and non-contact forces. Forces can be added up as vectors.
contact forcesForce exerted between two objects when they are touching. are forceA push or a pull. The unit of force is the newton (N). that act between two objects that are physically touching each other. Examples of contact forces include:
Normal contact force
An object at rest on a surface experiences a reaction forceForce exerted in the opposite direction to an action force. perpendicular (normalActing at an angle of 90掳 to a surface or boundary.) to the surface. For example, a box on a table.
Tension
An object that is being stretched experiences a tensionPulling force exerted by each end of an object such as a string or rope. force. For example, a cable holding a ceiling lamp.
Friction
Two objects sliding past each other experience frictionA force that opposes or prevents movement and converts kinetic energy into heat. forces. For example, a box sliding down a slope.
Air resistance
An object moving through the air experiences air resistanceA force of friction produced when an object moves through the air.. For example, a skydiver falling through the air.
When a contact forcesForce exerted between two objects when they are touching. acts between two objects, both objects experience the same size force, but in opposite directions. This is Newton's Third Law of Motion.