Force is an external agent capable of changing the state of rest or motion of a particular body. It has magnitude and direction. The direction in which the force is applied is known as the direction of force and the point where force is applied is called the point of application.
Whenever there is an interaction between two objects, there is a force that acts upon each of the objects. When the interaction ceases, the two objects no longer experience any force. Forces exist only as a result of an interaction.
Force takes a number of forms such as short–range atomic forces, electromagnetic forces, impact forces and gravitational forces. Force is a vector quantity that has both direction and magnitude.
The SI unit of Force is newton (N). One Newton is defined as a unit of force which would increase the velocity or accelerate a mass of one kilogram by 1 Metre per Second every second.
Few of the common Non-SI units of force are lbf, kgf, dyne, etc.
That means the acceleration of an object is directly proportional to the net force that acts on the object. This is usually in the direction of the net force, and is inversely proportional to the mass of the object.
Load is a term frequently used in engineering which means the force exerted on a surface or a body.