# Newton's Second Law

## Newton’s Second Law

Newton’s second law is, perhaps, his most famous law.

## F=ma

**Force = mass x acceleration**

**F = ma**

Force is measured in Newtons (N)

Mass is measured in kilograms (kg)

Acceleration is measured in metres per second squared (m/s2)

## Inertia

From the equation it is clear to see that if we increase the mass, we have to increase the force applied in order to maintain a constant acceleration. This was mentioned in the previous learning episode. **Inertia** is *a measure of how difficult it is to change the velocity of an object*. In order to change the velocity you need to change the acceleration and in order for that to occur, a change in force. The mass in the equation F = ma is sometimes referred to as inertial mass for this reason.

## Approximate

A small point in the grand scheme of the course but you need to know that mathematical symbol for **approximately**.

Here it is:

- A bus that accelerates at a rate of 0.5m/s2 when 5 people push it, each with a force of 750N, what is the mass of the bus?
- Your answer should include: 7500kg / 7500
- A car accelerates at a rate of 5m/s2. If it weighs 500kg how much driving force is the engine applying?
- Your answer should include: 2500N / 2500