Previous| Next

Gravitational force - how does it work?

The honest answer is that we do not know. We know that gravitational force is the weakest of all the fundamental forces that we know about. We know that it acts between all particles or objects with mass. We know the strength of the gravitational force between two objects depends upon the masses of the objects and their distance apart and can be worked out as:

where G is the universal gravitational constant; M and m are the masses of the objects; and R is the distance between their centres of mass.

What this means is that the Earth is attracted to you by the same force as you are attracted to the Earth. Should you choose to jump out of a 10th floor window, the Earth will be attracted up towards you as you are attracted down towards it. Obviously the Earth doesn't accelerate as much as you do (because it's so massive), so you only notice yourself falling. But, technically, it is coming up to meet you!


G = gravitational constant
M = mass of the Earth
m = mass of you
R = distance between you = radius of the Earth

From your point of view :

F = mg where g is acceleration due to gravity, so:

which works out to

for you at the surface of the Earth

From the Earth's point of view :

where m is your mass in kg

You can easily work out that the acceleration experienced by the Earth is quite tiny…

There is no explanation….

What no one can tell you is how gravity works. Scientists are still working on explanations for gravity. Some scientists are working on detecting 'gravitons', which have been suggested as the 'exchange particle' that carries the gravitational force. Others are looking for the Higgs boson, which Higgs suggested as being what allows particles to have mass. All this is in the future. For now we have to be satisfied with the basic statements of fact about gravity and wait a little longer for a real explanation.

Previous| Next


Messages from Space home | Schoolzone home | Orbits home | Orbits: Gravitational force