Objects do not start to move by themselves. Anything that pushes or pulls an object is called a force. A breath of wind, a car engine, a magnet or an elastic band are all examples of things that can produce a force. Gravity is an important force. You can see it at work if you let a pen drop. The pen is being pulled towards a very large object, the Earth itself.

Direct or distant force?

Some forces work when an object is pushed or pulled by another. These are direct forces. Other forces make things move without contact. One example is gravity: the pen drops to the ground due to an unseen force. Another is magnetism: a magnet can pull a piece of iron towards it without touching it. These are called distant forces.

Even still objects have forces acting on them. In this tug-of-war contest, one team is pulling in one direction, while the other team is pulling in the opposite direction. Because they are both pulling with exactly the same force, neither is moving anywhere. This is because when forces are balanced, they cancel each other out.

At the same time, there is another force at work. The cables attached to the Chair-o-Plane are pulling us in towards the roundabout. They keep us moving in a circle around it. This force is called the centripetal force. It is these same two balancing forces, the centrifugal and centripetal forces, that keep the Earth and other planets travelling in orbit around the Sun. In this case, the Sun’s centripetal force is invisible: gravity.