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All objects fall at the same rate,why would you than fall faster in a neutron star?

by Jarfi
Tags: fall, faster, neutron, objects, rate, star
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Jarfi
#1
Mar30-11, 06:17 PM
P: 273
So according to all if you drop a feather and a bowling ball on earth in vaccum it falls at the same speed. So that says acceleration of gravity is not affected by mass only the momentum.

And this says that even a moon size iron ball would fall at the same speed to the earth as a feather(in vaccuum)

And therefor if a black hole would fall on the earth(earth gets sucked in) it would suppost to fall at the same speed as the feather.

But that tells us that the speed of gravity is the same no matter what? and that is not true because we all know that when you jump at the moon it takes longer for you to fall down than if you where thrown at a neutron star or a black hole, you would accelerate extremely fast and die.

So that tells us that more mass=more/faster acceleration



So you put two neutron stars next to each other, they merge very fast(right?)

And put two earths next to each other, it takes more time for them to collapse

I am just confused why you say no matter what the weight is velocity is always the same but you fall at light speed(at least very fast) into a black hole....
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Nabeshin
#2
Mar30-11, 07:12 PM
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Quote Quote by Jarfi View Post
But that tells us that the speed of gravity is the same no matter what? and that is not true because we all know that when you jump at the moon it takes longer for you to fall down than if you where thrown at a neutron star or a black hole, you would accelerate extremely fast and die.
Not at all. I think part of this misunderstanding comes from the lack of precision in statements you've heard about gravity, so here's a correct one:

In the absence of other forces, the rate at which an object falls in a gravitational field is independent of its mass or composition provided that mass is much less than the mass of the object creating the gravitational field.

To be even more precise, a bowling ball does "fall" faster than a feather. Why? Because the bowling ball "pulls the earth up" more than the feather, so the two meet slightly quicker. In the rest frame of a bloke on the Earth, this looks like it is falling faster. But the magnitude of this effect is perilously small, something like one part in 10^24, well beyond anything we could hope to detect. Now, if you take the moon and drop it, the earth responds significantly to the Moon's gravitational field, and this is detectable.

To move off the earth, the acceleration felt in a gravitational field (again, for objects of negligible mass) is determined by the mass of the object creating that field. So, as measured the same distance away from the object, a star would cause higher acceleration than the earth.

I could go on, and will if it enhances your understanding, but does that clear up the issue so far?
russ_watters
#3
Mar30-11, 08:03 PM
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Another rewording: The bowling ball falls to earth at the same rate as the feather, but the earth falls to the bowling ball faster than it falls to the feather. They fall toward their common center of mass, not toward the center of the earth.

Jarfi
#4
Mar30-11, 08:06 PM
P: 273
All objects fall at the same rate,why would you than fall faster in a neutron star?

Quote Quote by Nabeshin View Post
Not at all. I think part of this misunderstanding comes from the lack of precision in statements you've heard about gravity, so here's a correct one:

In the absence of other forces, the rate at which an object falls in a gravitational field is independent of its mass or composition provided that mass is much less than the mass of the object creating the gravitational field.

To be even more precise, a bowling ball does "fall" faster than a feather. Why? Because the bowling ball "pulls the earth up" more than the feather, so the two meet slightly quicker. In the rest frame of a bloke on the Earth, this looks like it is falling faster. But the magnitude of this effect is perilously small, something like one part in 10^24, well beyond anything we could hope to detect. Now, if you take the moon and drop it, the earth responds significantly to the Moon's gravitational field, and this is detectable.

To move off the earth, the acceleration felt in a gravitational field (again, for objects of negligible mass) is determined by the mass of the object creating that field. So, as measured the same distance away from the object, a star would cause higher acceleration than the earth.

I could go on, and will if it enhances your understanding, but does that clear up the issue so far?
Mercy! I think I get it now.

A star pulls all objects at the same speed but the reason heavier objects fall faster is because they pull the star themselves more! So in the end all objects fall at the same speed but heavier objects land sooner because they pull their landing site thorwards them:)

Is my conclusion correct?
Jarfi
#5
Mar30-11, 08:08 PM
P: 273
Quote Quote by russ_watters View Post
Another rewording: The bowling ball falls to earth at the same rate as the feather, but the earth falls to the bowling ball faster than it falls to the feather. They fall toward their common center of mass, not toward the center of the earth.
Thanks man it's a good and simple law
Zeus_85
#6
Jan7-12, 06:10 PM
P: 1
Not sure if I'm right here? but isn't Gravity merely: The sun spinning and inducing a centripetal force, While the Earth so far away making another centripetal force but weaker than the sun for its less mass and smaller surface area. This means the sun and other planets like Jupiter with their superior size and mass is what prevents the earth getting sucked into the sun. So when we throw a small object on earth such as a rock our centripetal force and our superior mass is what makes such a force to exist and keep our objects on the ground.

This may mean from the big bang everything exploded. everything was super heated atoms cooled down then made bonds. Those then made rocks colliding with each other pushing smaller masses further apart till there is a planetary equilibrium.
alexg
#7
Jan7-12, 10:36 PM
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P: 126
All objects in a given gravitational field fall at the same rate.

But the gravitational field of a neutron star is much stronger than that of earth, so objects fall faster on the neutron star than on earth.

Not sure if I'm right here? but isn't Gravity merely: The sun spinning and inducing a centripetal force, While the Earth so far away making another centripetal force but weaker than the sun for its less mass and smaller surface area. This means the sun and other planets like Jupiter with their superior size and mass is what prevents the earth getting sucked into the sun. So when we throw a small object on earth such as a rock our centripetal force and our superior mass is what makes such a force to exist and keep our objects on the ground.
No. Gravity has nothing to do with rotation, and everything to do with mass (or it's energy equivalent).
Lsos
#8
Jan9-12, 03:05 AM
P: 777
Quote Quote by Jarfi View Post
Mercy! I think I get it now.

A star pulls all objects at the same speed but the reason heavier objects fall faster is because they pull the star themselves more! So in the end all objects fall at the same speed but heavier objects land sooner because they pull their landing site thorwards them:)

Is my conclusion correct?
Yes...but you will only notice this effect with comparable masses. The earth is very massive, so you will not notice this effect with everyday objects, such as a feather, a bowling ball, a car, or even a building. They just on't pull up on the earth by any appreciable amount.

The moon, however, DOES pull on the earth by a measurable amount. So if we dropped the moon, it would contact with the earth faster than if we dropped a feather.


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