Newton's Second Law

Newton's Second Law is concerned with unbalanced forces. Unbalanced forces produce acceleration. The greater the unbalanced force the greater the acceleration. This law is usually written as an equation:

Unbalanced\,force = mass \times acceleration

F = m \times a

Where unbalanced force is measured in Newtons ( N), mass in kilograms ( kg) and acceleration in metres per second per second ( m\,s^{-2})

Remember that it is an unbalanced force that is required here.



A car's engine force is 3000 N and its mass is 1500 kg.

A frictional force of 500 N acts over a distance of 20 m.

Calculate the acceleration of the car.

Unbalanced force:

F = 3000 - 500

= 2500N

F = m \times a

a = F \div m

= 2500 \div 1500

a = 1.67\,m\,s^{-2}

The acceleration of the car is 1.67 m\,s^{-2}.


Calculate the work done in moving the car against friction.

{E_W} = F \times d

= 500 \times 20

= 1000J

Work done against friction moving car = 1000 J.

Newton's Second Law