degrees of gravity?

[claymore]

Does an objects mass determine the effect that gravity has on it or is it the same for everything from a feather to a planet?

[Doc Spock]

Mass attracts mass. This is the fundamental principle of gravity.

However things can fall to Earth at different speeds. Terminal velocity. Humans about 120 mpm. Cats about 60 mph. Feathers very slow. It is all to do with build up of air pressure below falling object.

Basically the "pull" is stronger relative to mass/density.

[New Judge]

The Doc�s explanation has nothing to do with gravity, but with the varying effects that air resistance has upon different bodies.

The Earth�s surface gravity has the effect of accelerating any mass by 32 feet (about 9.8 metres) per second per second. This is irrespective of the amount of mass. If you were able to drop a car and a feather from the same height in a vacuum, they will take the same time to reach the surface.

In the atmosphere, of course, the feather will float gently down whilst the car will crash to the surface. But it is the effect of air resistance that makes this difference, not the mass of the object being attracted.

The "terminal velocities" mentioned by the Doc are also to do with air resistance. The 120mph quoted for humans is the velocity at which normally a human body will no longer accellerate (in the lower atmosphere) no matter how far it has to fall. This is reached in about 5 seconds after the decent begins. The resistance of the atmosphere is then so great that gravity can no longer accelerate the human body. However, terminal velocity can be increased if the falling body adopts streamlining techniques such as posture or smoothed clothing.

[jake-the-peg]

Lets see if I can clarify this.

Mass has 2 effects it's mutual attraction (gravitational mass) and it's resistance to force (Inertial mass)

The reason that one body is heavier than another is that there is a greater attractive force between it and the Earth than an object with less mass.

F= G(M1xM2)/r�
G is a constant and M1 is the mass of the object and M2 is the mass of the Earth. As M1 gets bigger so does the force.
The force F is what we see as weight.

Now if we drop them F=M1xa where a is the acceleration as it starts to fall so the mass of the object cancels

F= G(M1xM2)/r�=M1xa

a=GxM2/r�

This means that any body accelerates and falls at the same speed , whether it's a hammer or a feather as proved by Apollo 15 when they did this and showed that a hammer and a feather did indeed hit the ground at the same time providing that there's no air resistance

[mibn2cweus]

Gravity is a mutual effect between two objects in proportion to their combined mass. While a planet accelerates a feather towards it centre of gravity, a feather likewise accelerates a planet towards its centre of gravity. It is the mass of each object that determines the degree of acceleration each contributes to the combined mutual gravity between them. For objects contributing only a tiny fraction of the total combined mass, the contribution they make to the total effective gravity can usually be ignored.

Our Moon has only about 1/80th the mass of the Earth but if it were not for its own gravity its orbit would be slower or further from the Earth.