# Would the ISS and the moon fall to earth and stop orbiting if they there werent accelerating forward?

and in case of the moon whats giving it forward acceleration

Update:

lets say human was left to float in earths orbit, obviousely he will be falling, but wil he start to orbit as well, the forward momentum is it given by earths gravity?

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• RickB
Lv 7
8 years ago

Yes. If some force were to slow the moon to a complete stop, the earth's gravity would cause it to fall straight down into the earth (this would take a few days since the moon is so far). The same thing would happen to the ISS if its forward motion were stopped for some reason.

> "in case of the moon whats giving it forward acceleration"

"Acceleration" has a different meaning in physics. A better way to express this question is: "What's giving the moon its forward momentum?"

The moon is using "fossil" momentum that was given to it when it formed, which was probably due to a collision between the earth and an ancient small planet billions of years ago. The thing about momentum is that it STAYS WITH an object forever unless something slows the object down.

This is something that Isaac Newton taught us in his three Laws of Motion. He showed that our everyday intuition about moving objects is wrong.

In much of our everyday experience, we notice that things slow down to a stop unless something keeps pushing them. So our intuition is that, when a moving thing is "left alone," it will slow down and stop. But Newton looked at it a different way. He pointed out that, all those slowing-down things aren't really "left alone" at all, but they are being resisted by things like friction and air resistance. He said that if you remove all that resistance, and TRULY left the object alone, it would continue its motion basically forever.

That's the way we look at the moon's motion today. Since there is no air resistance or other friction to slow it down, it just keeps going. Newton called this property "inertia"; the tendency of an object to maintain its state of motion.

> "human was left to float in earths orbit...wil he start to orbit as well, the forward momentum is it given by earths gravity?"

This is an interesting qestion. If the human is initially *completely* stationary with respect to the earth, then gravity will pull him straight down, and he will certainly collide. In that case the earth's gravity certainly gives him extra momentum, but it is pointed straight down!

But if he has *some* initial sideways momentum, his fate may be different. In this case, the earth's gravity will curve his path. His path will be a combination of his initial sideways momentum and the downward influence of gravity. So the question is, how sharply is his path curved? If the gravity is strong and his initial momentum is small, the curvature will be rather sharp, and his path will intersect with the earth's surface (ouch!) On the other hand, if his initial sideways momentum is sufficiently great (and/or gravity sufficiently small), the curvature of his path may be gentle enough that he manages to "miss" the surface of the earth. In that case, he will swing around the earth and come back to his initial position again, and continue around like that in orbit.

(There is also a third possibility: If his sideways speed is *very* great, he will go into a path that does not return to the earth at all. This speed is the so-called "escape velocity".)

• 8 years ago

1. Would the ISS and the moon fall to earth and stop orbiting if they there weren't accelerating forward? No. For an object to remain in orbit around the Earth, it has to maintain a speed in which its inertia would equal the influence of Earth's gravity.

2. and in case of the moon whats giving it forward acceleration? The reason the moon is accelerating is because it is being "pulled" by the bulge near the equator. Since this bulge is moving at the same speed as the Earth rotates, which is faster than the speed that the moon is orbiting, it is causing the moon to accelerate. This is also causing the moon to recede (pull away) from the Earth. The moon's gravitational influence is also causing the rotation of the Earth to slow.

3. lets say human was left to float in earths orbit, obviously he will be falling, but will he start to orbit as well, the forward momentum is it given by earths gravity? This would depend on where the human was when he was left and in which direction he was going at that time. If the human was already moving toward Earth, he would continue to move toward it and be accelerated by the Earth's gravity. However, if he was left beyond the Roche Limit (approximately 14,000 miles above the Earth) and he was moving away from the Earth, his inertia would equal or even exceed Earth's gravitational influence.

• 8 years ago

Well, ..., in short, Yes.

A little more detail is needed here. Neither moon or ISS are accelerating. They have enough forward momentum that for every 'unit of of distance' that they move forwards and away form the Earth, Earth's gravity pulls them back them exact same 'unit of distance'. If all forward motion were to stop both would spiral (fall) into the Earth.

It's hard to say what gave the moon it's original forward momentum because we really don't know if it was a captured body, the result of an impact, or a portion of the Earth "slung" off during primordial formation. I know the popular theory is the impact theory but at the end of the day they're all just educated speculations. Suffice it to say, that whatever happened, there is sufficient forward momentum in he moon's tangential motion to keep it in orbit and from spiraling into the earth.

• 4 years ago

If the Moon stopped it could fall to Earth. think of you had a effective magnet interior the palm of your hand and a string with fairly iron tied on the top. Now that's a effective magnet so in case you carry the string so a methods because it could pass and permit pass it could get sucked into the magnet. it fairly is fairly like what the Moon could do if it became no longer revolving around the Earth. Now in case you have been to spin the piece of iron quickly adequate in a circle that's going to stay faraway from the magnet on your hand. in case you gradual the cost of twirling there'll attain a component the place it is not solid adequate to overcome the magnet. The solar and different greater great planets do have greater gravitational pull than the Earth yet whilst the moon have been to detach from the Earth, by some skill, it is not going they could undertake the moon into their orbit(The solar is a lot to special it could swallow the moon until the moon became shifting at freaking quickly speed). The moon could might desire to first pass on the suitable distance from the planet on the suitable speed to no longer triumph over/undercome the gravity. besides the fact that that's achieveable, if it got here out of Earths orbit by some skill.

• Lesus
Lv 7
8 years ago

They would fly away in straight lines if gravity wasn't accelerating them toward the earth.