When a force acts on an object that is moving, or able to move, there is a change in momentumA quantity relating to a moving object that is calculated by multiplying its mass by its velocity.:
in equations, change in momentum is shown as \(m \Delta v\)
\(\Delta v\) is the change in velocity (∆ is the Greek letter delta, representing 'change in')
Calculating rate of change of momentum
The two equations can be combined to show how to calculate the force involved when a change in momentum happens:
Acceleration (a) appears in both equations, giving:
\(force = \frac{change~in~momentum}{time~taken}\)
\(F = \frac{m \Delta v}{\Delta t}\)
This is when:
force (F) is measured in newtons (N)
change in momentum (m∆v) is measured in kilogram metres per second (kg m/s)
time taken (∆t) is measured in seconds (s)
The equation shows that the force involved is equal to the rate of changeThe ratio showing how the value of an amount varies in relation to another. of momentum.
Example calculation
A 1,500 kg car accelerates from rest to a velocity of 30 m/s. This takes 20 seconds. Calculate the force acting on the car.
