DEFINITIONS: MECHANICS 2

1. Force
   Anything that causes the velocity of an object to change is called a force.
   
   
2. Mass
   The mass of a body is a measure of how difficult it is to accelerate that body.
   The unit of mass is the kilogram.
   
   
3. Weight
   The weight of an object is the force of the Earth's gravity acting on it.
   
   
4. Momentum
   Momentum is the mass of an object multiplied by it's velocity.
   The unit of momentum is the kilogram metre per second (kg m s^-1)
   
   
5. Newton's Laws of Motion
   Newton's first law of motion:        (MIX)
   Every body will remain in a state of rest or travelling with a constant velocity
   unless an unbalanced external force acts on it.
   
   Newton's second law of motion:     (MIX)
   When an unbalanced force acts on a body the rate of change of the body's momentum
   is directly proportional to the force and takes place in the direction of the force.
   
   Newton's third law of motion:      (MIX)
   If a body A exerts a force on a body B,
   then body B exerts an equal but opposite force on body A,
   i.e. For every action there is an equal and opposite reaction.
   
   
6. The Principle of Conservation of Momentum      (MIX)
   In any interaction between two or more bodies
   the total momentum of the bodies before the interaction
   is equal to the total momentum after the interaction
   provided no external force acts on the system of bodies.