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Re: Gravity...... Is a force!
Posted by 'davidmc' on 03 Jan 2011 @ 16:10

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davidmcJoined: April 2003
Total Posts: 2
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Chris,

You have misunderstood and/or I haven't explained myself well enough. However, you are quite clearly totally incorrect.

CHRIS SAID: "So if force is equal to mass times gravity, how can gravity actually be a force!? You have substituted a (for acceleration) with g (gravitational acceleration) i.e. gravity!"

g IS NOT gravity, it is the acceleration due to the FORCE OF GRAVITY. It only appears to be a constant here on earth because the earth has constant mass that is considerably greater than our mass.

There are four forces in the universe, strong nuclear, weak nuclear, electromagnetic and gravity.

Gravity isn't something that only occurs here on earth or planets or stars or moons. Sticking to the simple Newtonian model of gravity, all mass has gravity. That is to say, anything with mass will be attracted to anything else with mass (a bit like magnets). However, gravity is an extremely weak force (the weakest of all four fundamental forces). It's weak enough that we can all stand up, put rockets into space and bounce a ball.

Imagine two 2kg cannon balls in the middle of outer space with nothing else around. These two cannon balls are positioned 1m apart. The force due to gravity attracting these cannon balls together is F = G* (2*2/1) where G is the GRAVITATIONAL FORCE CONSTANT.

Since G = 6.67300 × 10-11 m3 kg-1 s-2 = 0.0000000000667300 (it's the same number anywhere in the universe; on the surface of the sun, in the middle of outer space, here on earth etc)

the force due to gravity attracting these two cannon balls = 0.00000000006673 * 4 = 0.00000000026692N

Newton's first law says:

"Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it."

That is to say, an object will not accelerate, deccelerate or change direction unless a force is applied to it. In your example, the "gravitational acceleration" is a result of the force of gravity, not the cause of it.

The concepts above are still in use today and were good enough to put man on the moon. Einstein surpassed the Newtonian model of gravity with his General Theory of Relativity, in which he created the concept of space-time being "curved" by mass. This solved some anomolies with the Newtonian model, the most obvious of which is that the proton (which has no mass) is also affected by gravity. However, the Newtonian model is good enough for large objects at low speed.

Message Thread:

Gravity...... by 'Newshound' (29 Dec 2010 @ 20:03)

Re: Gravity...... by 'HarryC' (29 Dec 2010 @ 20:59)

Re: Gravity...... by 'John' (29 Dec 2010 @ 23:36)

Re: Gravity...... by 'Newshound' (29 Dec 2010 @ 23:51)

Re: Gravity...... by 'alanrr' (30 Dec 2010 @ 11:23)

Re: Gravity...... by 'rich84' (30 Dec 2010 @ 15:10)

Re: Gravity...... by 'Newshound' (30 Dec 2010 @ 16:01)

Re: Gravity...... by 'Tmoon' (01 Jan 2011 @ 15:16)

Re: Gravity...... by 'colingray' (02 Jan 2011 @ 9:41)

Re: Gravity...... by 'ChrisAdams' (02 Jan 2011 @ 10:55)

Re: Gravity...... by 'colingray' (02 Jan 2011 @ 19:24)

Re: Gravity...... by 'ChrisAdams' (02 Jan 2011 @ 22:01)

Re: Gravity...... by 'colingray' (03 Jan 2011 @ 1:39)

Re: Gravity...... by 'glittttt' (03 Jan 2011 @ 12:32)

Re: Gravity...... by 'colingray' (03 Jan 2011 @ 12:47)

Re: Gravity...... Is a Force by 'davidmc' (03 Jan 2011 @ 13:19)

Re: Gravity...... Is an acceleration! by 'ChrisAdams' (03 Jan 2011 @ 14:45)

Re: Gravity...... Is an acceleration! by 'colingray' (03 Jan 2011 @ 15:34)

Re: Gravity...... Is an acceleration! by 'colingray' (03 Jan 2011 @ 15:37)

Re: Gravity...... Is a force! by 'davidmc' << You are here!

Re: Gravity...... Is a force! by 'colingray' (03 Jan 2011 @ 17:16)

Re: Gravity...... Is a force! by 'ChrisAdams' (03 Jan 2011 @ 18:47)

Re: Gravity...... Is a force! by 'davidmc' (03 Jan 2011 @ 19:31)

Re: Gravity...... Is a force! by 'ChrisAdams' (03 Jan 2011 @ 20:32)

Re: Gravity...... Is a force! by 'SimonS' (08 Jan 2011 @ 16:20)

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