Have you ever noticed the feeling you get when you are in a car, and the car takes a curve? It’s like someone is constantly pulling you outwards and forcing you to not move along the curved road. What causes that feeling? Why is that if you rotate anything in a circle, let it gain speed and then let it go, it goes straight forward with so much force? Things of this sort have one thing in common; they all involve the movement of an object in a circle.
Isaac Newton, a 17th-century physicist, came up with some explanations as to why things work the way they do. He proposed three laws describing some of the most basic workings of the universe. We know these laws as Newton’s laws of motion. For our subject, we can ignore two of the laws. The law that concerns us is the third law of motion.
According to the third law, everything that happens also has a consequence. We can’t throw a ball at the wall and not expect it to return, and we can’t force two things to collide and just come to a stop without bouncing back or breaking down. Whatever happens first, causes a reaction that is equally powerful and is in the opposite direction. That is why the harder you throw the ball at the wall, the faster it comes back. Forces have reactions.
Keeping that in mind, let us come back to the forces governing circling objects. First of all, how do we get something to move in a circle? We must do it by using some kind of force. Let us consider an example.
If you tie a weight to the end of a string and whirl it round and round in a circle, the weight tries to fly away in a direction at right angles to the string. The string compels it to follow a circular path, so the string is pulled on by the weight, or to look at the matter the other way round, the string pulls on the weight – with a force which is called the centrifugal force. The direction of the force that we are applying on the stone is actually always towards the center (our hand) rather than directed along the circular path of the stone’s rotation. We don’t feel it because the stone is moving too fast. It means that we are pulling on the stone inwards so fast that it in order to keep up, it moves in a circle.
But, according to Newton’s third law, if there’s a force pulling the stone inwards, there must be an equal amount of force pulling it outwards. We call this force the centrifugal force. It is also called a “fictitious” force because we never get to see its effects. It is simply a counter-effect of the centripetal force.
The centrifugal force increases much more quickly than the number of revolutions per minute. The best example of this phenomenon is the swings ride (see photo), each seat of which, suspended by a chain, tries to fly away when the wheel revolves at high speed.
A practical example involving the apparent effects of centrifugal forces is that of an instrument called the centrifuge. The speed of many engines is controlled by a centrifugal governor, with whirling balls that fly further apart as the speed increases and moves levers that reduce the supply of steam or gas. Centrifugal apparatus is also used to separate cream from milk, water from wet clothes, and molasses from sugar. Pipes are cast centrifugally by pouring molten metal into rapidly revolving molds. Centrifugal force keeps a circular saw stiff, is applied to the pumping of water, and is depended on to release the safety-belt in a shell fuse as the shell leaves the gun. In a Wall of Death, the centrifugal force keeps a car moving in a circle by keeping it pushed against the walls.
We don’t get to hear a lot of uses of this kind of force as, mostly, we use terms such as “gravity” and “friction” to explain stuff. However, a centrifugal force can always play a role as long as there is a centripetal force.
Centrifugal force (Wikipedia)