Why does the Moon stay in its orbit around the Earth?

What is a force? There is no easy answer to this question. We all know what forces do, for example make an object move or change the shape of an object. The force that has most influence on us is probably gravitational force, without it we wouldn’t be able to stay on the Earth’s surface. Another interesting force is the centripetal force, the force which causes an object to stay in the same orbit around another object. Without the centripetal force moving object would immediately move away from the central object.

An easy example of this is when someone has a piece of string with a heavy object attached to the end of the string. Whenever he holds on to the empty end of the string and he starts moving the heavy object in an orbit around his hand, the string makes sure the object doesn’t fly away. In this case, the string provides the centripetal force. If the string would suddenly snap or the person let go of it, the centripetal force would disappear and the object would move on in a straight line (as shown in the image by the green arrow).

This is the point where it gets a little more complicated. We can now conclude the fact that the heavy object has in fact been moving in a straight line all the time. However, the centripetal force pulled the object slightly towards the centre at every single point in the circle, making sure the object almost ‘’falls’’ towards the centre all the time. This way the object stays in its orbit.

We can now answer the main question in this post: Why does the Moon stay in its orbit around the Earth? The answer to this seems obvious, however, which force provides the centripetal force in the case of the Moon and the Earth? According to Newton’s second law of motion, every object in the universe attracts every other object in the universe. This happens because of a force called gravity. The combined gravity of the Earth and the Moon (centripetal force) cause the Moon to be in a constant ‘’freefall’’ towards the Earth, and thus making sure the Moon stays in its orbit around the Earth.