Force
Anything that causes the of an object to change is called a force.
Mass
The mass of a body is a measure of how difficult it is to that body. The unit of mass is the .
Weight
The weight of an object is the force of the Earth's acting on it.
Momentum
Momentum is the of an object multiplied by its . The unit of momentum is the kilogram metre per (kg m s-1)
Newton's Laws of Motion
Newton's first law of motion:
Every body will remain in a state of or travelling with a constant unless an unbalanced external acts on it.

Newton's second law of motion:
When an unbalanced acts on a body the rate of change of the body's is proportional to the force and takes place in the of the force.

Newton's third law of motion:
If a body A exerts a on a body B, then body B exerts an but opposite force on body A,
i.e. For every action there is an equal and opposite .
The Principle of Conservation of Momentum
In any between two or more bodies the momentum of the bodies the interaction is equal to the total momentum the interaction provided no force acts on the system of bodies.