The state of motion of an object can be changed by the application of a force. A force is any interaction that changes the motion of an object. Forces can be either contact forces or non-contact forces. Contact forces are forces that are applied to an object by direct contact, such as pushing or pulling. Non-contact forces are forces that are applied to an object without direct contact, such as gravity or magnetism.

The net force acting on an object is the vector sum of all the forces acting on the object. If the net force is zero, the object will remain in its current state of motion. If the net force is not zero, the object will accelerate in the direction of the net force.

The magnitude of the acceleration is directly proportional to the net force and inversely proportional to the mass of the object. This relationship is known as Newton's second law of motion.

$$\sum F = ma$$

Where:

* F is the net force acting on the object (in Newtons)

* m is the mass of the object (in kilograms)

* a is the acceleration of the object (in meters per second squared)