Forces and Motion: Momentum

Momentum is a vector quantity which means it has both magnitude and direction.
The momentum of a body is calculated by multiplying its mass by its velocity. For example, a car moving at 20 m/s with a mass of 1000kg has a momentum of 20000 kg m/s.
When two or more objects interact in an isolated system, the total momentum before the event is equal to the total momentum after the event. This is known as the law of conservation of momentum.
Impulse is the change in momentum of an object when a force is applied. It is calculated by the equation: Impulse = Force x Time.
A larger force applied for the same time results in a larger change in momentum or impulse. Similarly, applying the same force for a longer time period also results in a larger impulse.
During a collision, the time for which the force is applied can be increased by using safety devices such as seat belts and air bags in cars. This reduces the force experienced during the collision and reduces injury.
The stopping distance of an object moving with a certain momentum can be calculated using the equation: Stopping distance = Initial velocity x Time taken to stop. The stopping distance will be longer for objects with a greater momentum.
Reaction time and braking force both affect the stopping distance of a vehicle.
Forces cause changes in momentum. For instance, gravity can change the direction of an object’s momentum without changing its magnitude.
Elastic and inelastic collisions refer to how momentum and kinetic energy are conserved. In an elastic collision, both are conserved. In an inelastic collision, momentum is conserved but kinetic energy is not.
Momentum is directly proportional to the mass and velocity of an object. This means that if you increase the mass or velocity, the momentum also increases. Likewise, reducing the mass or velocity will decrease the momentum.
When a force acts on an object moving in a straight line, it experiences a change in momentum proportional to the force and in the direction of the force. This is known as Newton’s second law of motion.