**Measuring forces **

You can use a device called a force meter to measure the size of a force. Most force meters have a hook that you can use to hang or pull on something. This will cause a spring to move and show you how much force is being applied.

We measure forces using a unit called Newtons. They get this name from one of the most famous scientists of all time – Isaac Newton. He was the first person to describe the force that we know as gravity.

A Newton can be described in another way, measured in kg*(m/sec2). You would read this as ‘kilograms times meters divided by seconds squared.’ This is because:

Force = Mass * Acceleration

Newton described this in his laws about physics which tell us that motion is created by unbalanced forces. He realized that objects that are not moving will remain still, and objects in motion will stay in motion unless a force interferes.

Force, mass, and acceleration are interrelated. If we know any two out of the three, we can find the third.

- Acceleration = Force / Mass
- Mass = Force / Acceleration

**Example**: Imagine two vehicles driving along the road with the same acceleration. One is a lorry and the other is a small car. The lorry has the larger force because it has a greater mass than the car. Now imagine two identical cars with the same mass. They move slowly and then gradually speed up. But one of the cars gets faster more quickly than the other one and overtakes it. We say that this car has greater acceleration. The car with the higher acceleration has the greater force.

**Measuring work **

In physics, work is defined as a force causing the movement—or displacement—of an object. In the case of a constant force, work is the scalar product of the force acting on an object and the displacement caused by that force. Though both force and displacement are vector quantities, work has no direction due to the nature of a scalar product (or dot product) in vector mathematics . This definition is consistent with the proper definition because a constant force integrates to merely the product of the force and distance.

To raise an object you have to do work to it. The work you have to do depend on the force on the object you are lifting and the distance you are going to raise it. Work is measured in units called JOULES.

Work = force x distance

A box exerts a force of 50 newtons on the ground. You want to lift it onto a table 1 metre high. The amount of work you have to do is 50 joules.

50 newtons (force) x 1 metre (distance) = 50 joules (work)