Momentum is a vector quantity, measured in Kgms-1.
Momentum = mass x velocity
p = mv
Newtons second law of motion - 'The acceleration of an object is directly proportional to the net force and inversely proportional to its mass'. This law can be written as F=ma, this can be changed to include momentum.
F=ma --> a = v - u / t
F= m (v - u / t) -------> mv - mu / t --------> change in momentum / time
F = change in momentum / change in time
F = delta (p) / delta (t)
The product of a force applied for a certain time is known as Impulse.
Impulse = change in momentum = Ft
Impulse = force x time
Ft = mv
Impulse in measured in Kgms-1 or Ns.
To stop something moving we need to remove all of its momentum. This idea allows us to calculate the impulse needed to stop a moving object.
Elastic Collisions - All momentum is conserved, Kinetic energyis conserved, relative speed of approach = relative speed of separation
Example of a perfectly elastic collision - a collision caused by non-contact forces, such as alpha particles being scattered by a nucleus.
Inelastic Collisions - All momentum is conserved, Kinetic energy is not conserved some is lost (usually as sound and heat), speed of separation has to be calculated.
In a perfectly inelastic collision the relative speed of separation is zero (objects stick together after collision and treated as one object)
Force - Time Graph
We can plot graphs of the force during a collision against time.
We can find the impulse, or change in the momentum, by calculating the area under the force-time graph.
Conservation of Linear Momentum
The principle of conservation of linear momentum can be used to predict the motion of objects after a collision.
The Principle of the Conservation of Momentum states: if objects collide, the total momentum before the collision is the same as the total momentum after the collision. (with the condition that no external forces act on the objects).