Question: What Causes Gravity?

Jacob Leygonie answered on 12 Nov 2019: last edited 12 Nov 2019 23:12

In classical physics, it is explained how different objects with different masses are all attracted toward each others.

The more mass an object has, the more powerful is the attraction it exerces on surrounding objects. As far as we are concerned, the planet earth is by far the most massive object in our environment. Its attraction power, which drags us on the ground, is what we call the gravity.

Three interesting related facts:

– As I said, every object exerces an attractive power on the other objects. So in particular we are, us humans, not only subject to the gravity (i.e the power of earth), but also to the attractive powers of any objects (toothbrushes, tables, chairs, friends). But those powers are negligible, since the masses of these other objects are incomparable with the one of the earth.

– If we were only subject to earth gravity, then we would directly be dragged into the center of the planet (and burn immediately). We know we don’t right? This is because there is another force, the reaction of the ground (that you feel on your foot when you stand) that balances gravity. These two forces, gravity and reaction, sum up to 0, and this is why we are in “equilibrium”.

– The attractive force that an object exerces on you also strongly depends on the distance that separates you from the object. So if we go far from planet earth, we do not really feel gravity. This is why for instance, in space, if one goes out of its space rocket, it is not dragged anywhere, since no object has enough attractive power at this distance. Moral: please do not go out of the space rocket!