Why Do Things Go In Circles
Have you ever tried to dip your hand in a bucket full of water and tried to whirl the water in a circle? Do you know of things which continuously go around in circles? I am sure that all of you must have seen or must be knowing of such things. All of us know about the International Space Station [ISS], it goes around the earth continuously at about 17,000 miles per hour. But why does it need to go so fast? Can’t it just apply breaks and slow down whenever it wants? And why do some satellites need to spin around planets so fast? We will try and answer some of these questions here.
To go around a circle we need a force which always acts, no matter what, towards the center of the circle. This is a pre-requisite for circular motion. Circular motion is never going to happen without this force. For the ISS it is provided by the earth’s gravity, for the earth to go around the sun the sun’s gravity is responsible for this (it goes around in an ellipse not exactly a circle, but the idea is the same in both case) and for the water whirling around in a circle the walls of the bucket are responsible for this force. This force which acts towards the center is called the centripetal force or the radial force. Now let me tell you an interesting fact, the objects which go around in a circle are actually going in a straight line while falling towards the center of the circle at the same time, this perfect combination of forces and velocity gives rise to circular so if the earth were to suddenly disappear the international space station would shoot off in a straight line. Just try and imagine how this happens and you will find it fascinating, trust me its art. Let me tell you. The ISS is going in a straight line but earth’s gravity pulls it towards itself, try and imagine, do you see it happening? The ISS is going straight, the earth is pulling it towards itself, but the ISS is so fast that by the time earth pulls it towards itself it has traveled to a different point. So that’s why it keeps going around and never falls to the earth. This is the reason why the speed is so critical. It is like salt in food, it has to be perfect. If the speed is too less it would fall to the surface of the planet, If the speed is too high then earth’s gravity would not be sufficient to pull it towards itself and thus the ISS would escape earth’s gravitational pull and go off into space (this speed is called escape velocity, its 11.2 kilometres per second for earth, any object exceeding this speed can escape earth’s gravitational pull). This is the reason why the ISS must go so fast otherwise it would fall to the surface.
Well, isn’t it amazing? I find it super interesting just try and imagine how these things take place and you will realize how beautiful this planet is and so is physics.
