Newton’s Second Law

We already know, from Newton’s First Law, that everything has a natural tendency to maintain the same motion when all the forces acting on an object are balanced. But what happens when the forces are not balanced?

That is where Newton’s Second Law comes in.

Newton’s Second Law tells us that an object will accelerate when it is acted on by an unbalanced force and the magnitude of the acceleration will be equal to the magnitude of the force divide by the mass of the object.

Newton’s Second Law is summarised in the equation; acceleration = force / mass

More commonly, Newton’s Second Law is stated in a slightly different form, as;

force = mass x acceleration

No matter how we arrange the equation, the meaning is the same: if the same unbalanced force is applied to two different objects, the object with the smaller mass will experience the greater acceleration.

But what do we mean by acceleration?

In everyday language we tend to link acceleration to an increase in speed but that is not the whole picture.

Acceleration is actually a change in velocity, which is itself a combination of speed and direction of travel. Any change in speed or any change in direction is actually a change in velocity – and any change in velocity is an acceleration.

So Newton’s Second Law tells us that when there is an unbalanced force acting on an object, the object’s speed may change or its direction of travel may change (or both).

In the exam, you are most likely to be asked to recall and use the equation for Newton’s Second Law but you might also be asked to explain the Law’s meaning verbally. In particular, you could be asked to give an example of a situation where an object is accelerating but its speed is not changing.

If you can’t think how this could be possible then please ask me because you definitely have to be able to solve this challenge.