Newtons first law

[JohnMitchell 16]

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There is a spot between the Earth and the moon that
provides an equal attraction. There used to be a
group called the "L5 Society". It wanted a stable
space colony by 1995.

The distance between the Earth and Moon is about 238K miles. The gravitational mid point is about 214K from the Earth. The Earth is clearly the dominant gravitational partner of the pair.
As you well know, there is no limit to the distance an object's gravitational effects go, just a diminishing of those effects, the inverse square of the distance. This gravitational effect travels at the speed of light. As you leave one object and approach another, there will always be a point in space where the new object's gravity will become dominant.

That's my story and I'm sticking to it. Thanks for the debate.

[DanG 1]

If you managed to get yourself 100,000 miles out and were stationary in reference to the Earth (no small feat) you would hit the Earth going really gosh darn fast. Let's say that there's a hole through the center of the Earth that you could fall through, and that the Earth had been evacuated of all its air. Also, you need to assume that the Earth and you are the only bodies around. What would happen?

You would fall through the Earth and come to rest on the other side 100,000 miles out. An instant later you'd begin the journey in reverse.

The problem with relating this to escape velocity is that in our example there are only two massive bodies in the universe. In the real solar system, there are numerous massive bodies, most notably the sun. Escape velocity is how fast you need to be going to leave the gravity well of a given body and come under the more significant influence of another body. For the Earth it is about 25,000mph.

- Dan G

[Andrewwhyte 1]

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Reread the article. It states that escape velocity works regardless of vector, except for "downward". If you are accelerating directly at the planet, you will hit it.

Since you postulated starting a freefall at a given height all the acceleration and thus the motion would be directly at the planet. Just like in regular skydiving you will hit the planet.

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Kinetic energy away from a gravitational field coverts, through slowing and height, to potential energy. Once you begin to fall back, potential energy converts back to the original kinetic energy, with losses for friction, yes. Since we're talking about "in a vacuum", friction losses should be a minor factor.

Right, but you cannot achieve escape velocity using only the energy gained from the force that is equal to the one you are trying to overcome. In fact it is the same force but in the opposite direction going as coming. The further out you start, the weaker the initial acceleration so even though you do accelerate longer, you still do not achieve escape velocity. Look at the orbits of comets for example.

[JohnMitchell 16]

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Right, but you cannot achieve escape velocity using only the energy gained from the force that is equal to the one you are trying to overcome. In fact it is the same force but in the opposite direction going as coming. The further out you start, the weaker the initial acceleration so even though you do accelerate longer, you still do not achieve escape velocity. Look at the orbits of comets for example.

Ah, now I understand your objection. Yes, you are correct, you would not quite achieve escape velocity on your downward trip. I agree. If you check post #16 of this thread I said " I believe that if you started 100,000 miles out or so you'd be close to escape velocity ". The caveat is "close to". My advanced math skills are weak. I'm a rule of thumb guy. Maybe I should have said "possibly approaching"?

[Andrewwhyte 1]

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Ah, now I understand your objection. Yes, you are correct, you would not quite achieve escape velocity on your downward trip. I agree. If you check post #16 of this thread I said " I believe that if you started 100,000 miles out or so you'd be close to escape velocity ". The caveat is "close to". My advanced math skills are weak. I'm a rule of thumb guy. Maybe I should have said "possibly approaching"?

[gainer 0]

Here is something interesting I picked up.

Newton lived in what the 1500-1600? Lets go for arguments sake 1600. Now NASA did their first space walk in the 1950/1960, lets say 1960 for simplicity. It took the smartest people in the world, arguebly of course, 360 years to listen to him when he made that first, and third law, aka you atay still when there is no force and b) very action has .... First guy nearly died when they messed that up.

[SpeedRacer 1]

Fig Newton's First Law:

Oo-ee, gooey, rich and chewy inside.
Golden, flaky, tender cakey outside.
Wrap the inside in the outside -- Is it good? Darn Tootin'!
Doin' the Big FIG NEWTON (here's the tricky part), the big FIG NEWTON (one more time!), the BIG FIG NEWTONNNNN!!!

Speed Racer
--------------------------------------------------

[happythoughts 0]

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First guy nearly died when they messed that up.

How about that Mars Lander ? One little math error
and it is Mar's flattest extraterrestrial object.

"Frikkin' meters..."

[shropshire 0]

Hey, don't blame the units, blame that people that can't do maths.

(.)Y(.)
Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome

[happythoughts 0]

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Hey, don't blame the units, blame that people that can't do maths.

I've heard it said that if you halve the distance
between you and an object - and then do that
repeatedly, you'll never reach it.

That's how I stop at stoplights.

[muff528 3]

I've heard it said that if you halve the distance
between you and an object - and then do that
repeatedly, you'll never reach it.

Well, at least down to ~0.0000000000000000000000000000000000016 m. Then you either have to stop or go the rest of the way to the object.

[jakee 1,597]

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Here is something interesting I picked up.

Newton lived in what the 1500-1600? Lets go for arguments sake 1600. Now NASA did their first space walk in the 1950/1960, lets say 1960 for simplicity. It took the smartest people in the world, arguebly of course, 360 years to listen to him when he made that first, and third law, aka you atay still when there is no force and b) very action has .... First guy nearly died when they messed that up.

I don't follow...

Do you want to have an ideagasm?

[muff528 3]

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First guy nearly died when they messed that up.

How about that Mars Lander ? One little math error
and it is Mar's flattest extraterrestrial object.

Extramartial object

"Frikkin' meters..."

Agreed, but it's way better than BS or Whitworth.