A force is a push or a pull that acts upon an object as a results of its interaction with another object. Forces result from interactions!With Newtons ideas, whenever objects interact with each other, they make physical forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair forces upward force on your body.
There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces and are the subject of Newton's third law of motion.Newton's third law is: For every action, there is an equal and opposite reaction.