# Momentum of a Body

## Momentum of a Body

• Momentum is a vector quantity, which means it has both magnitude and direction.
• It is measured in kg m/s in the SI system.
• The equation for momentum (p) is mass (m) times velocity (v), or p=mv.
• If the velocity of an object is zero, then its momentum is also zero, regardless of its mass.
• The total momentum in a system is conserved in both elastic and inelastic collisions. This principle is known as conservation of momentum.
• In an elastic collision, both momentum and kinetic energy are conserved.
• In an inelastic collision, momentum is conserved but kinetic energy is not.
• Impulse is the change in momentum of an object when a force acts upon it for a moment of time. It is calculated by multiplying the force (F) by the time period (t) over which it acts, or Ft=∆p.
• Impulse is also a vector quantity and has the same direction as the force causing the change.
• The force required to change the momentum of an object depends on the time period over which the change occurs. A slower change requires less force.
• The longer the time period over which a change in momentum occurs, the lower the force required. This principle underlies the use of seatbelts and airbags in cars.
• The recoil of a gun or the propulsion of a rocket can be explained using the concept of momentum.
• When two objects interact, the force they exert on each other will be equal and opposite. This is Newton’s third law of motion and it often results in changes in the objects’ momentum.
• The rate of change of momentum is proportional to the force causing it and occurs in the same direction as the force. This is Newton’s second law of motion.