# DO objects fall at the same speed? NO!

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This is a completely aerodynamic argument. The guys saying heavier objects cut through air resistance more.

maybe he's momentum?

But really, if you had a bowling ball made of ceramic, and a bowling of the exact same shape made of lead, which would fall faster? I think that is his real argument.

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Why are you still replying to this thread? The O.P. is permanently banned from SFN for some reason.

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Why are you still replying to this thread? The O.P. is permanently banned from SFN for some reason.

I replied as danny8522003 asked a question. And I'm reading it now because I'm interested in what people have to say...

The momentu argument imo is not a good one as the air molecules are so small...

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You'd have to take into account the acceleration of the earth towards the sun aswell as the sun towards the earth... I think....

That's what i was trying to get at...

So why is the mass of the sun not accounted for in the equations?

$g = \frac{GM}{x^2}$

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That's what i was trying to get at...

So why is the mass of the sun not accounted for in the equations?

$g = \frac{GM}{x^2}$

Because that equation works out the acceleration of one body from a rest frame.

Use:

$F=\frac{-GMm}{r^2}$

Both objects are accelerating each other according to an initial rest frame:

F=ma not the same a as F=Ma

So a total acceleration towards each other would be the sum of the modulus of them.

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But if im on Earth, the Earth is at rest relative to me?

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For most calculations of this sort, it really doesn't matter what you assume to be at rest. Nothing is really at rest; so long as you are consistent and you take all vectors into account,t he answers will be the same, even if you assume that the earth falls toward people (it's just much simpler to consider it such that small objects fall toward large objects).

And once again, since some people don't get it still (though some clearly do, they just aren't being listened to:

There is a difference. Acceleration depends upon BOTH masses. However, as it has been stated, you can't prove this by dropping a ball and a feather toward the earth. It only becomes apparant when you a) do the math or b) use larger objects, such as the sun. The rate at which two objects move toward each other depends upon the mass of *both*, though when you use the Earth analogy, the mass of the earth is many magnitudes of order greater than a ball or a rock, so it drowns out the effects of gravity due to mass other than that of the earth. So the equation some of you are using (that only has the mass of the Earth or the force of Earths gravity) is a simplification - it will get you an answer good enough for a certain type of question.

However, fundamentally, truly, all things considered - he is right, she is wrong. Practically (in terms of how we as average people who have office jobs, not NASA jobs deal with this) she is right.

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Yeah i agree with you Matt, i just like being awkward.

Never liked Newton anyway .

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Sorry to double post...

After many many arguments and discussions with my physics teacher, i fail to see how $g=-\frac{GM}{x^2}$ would hold true.

If i dropped a black hole, and a hammer towards the Earth the acceleration would be a hell of a lot different if i were an observer, seemingly at rest, on the Earth. So then surely you MUST have to take both masses into account when calculating g. Is there a relativistic equation that works better than this Newtonian one?

If this is just a ballpark figure, then why is this a Law and not a theory?

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since in the rest frame of earth the whole frame is accelerating. subtract this acceleration and the blackhole accelerates towards earth at 9.81 ms^-2

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Hmmm... if by that you mean the Earth would be pulled towards the black hole far more quickly than the black hole would be pulled towards the Earth, then yeah... hence the hammer must also be constantly pulling the Earth towards it - only much slower than the black hole would be pulling the Earth towards it.

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since in the rest frame of earth the whole frame is accelerating. subtract this acceleration and the blackhole accelerates towards earth at 9.81 ms^-2

Im not sure i understand, how can we just subtract this frame?

Surely if this frame is moving from an outside observer the two masses are both accelerating toward each other. So if im at rest relative to the Earth, wouldn't i see the black hole accelerating towards me at >g?

Another way of looking at it: g for the black hole > g for the Earth. But how can you tell which is falling towards which since the claims from both frames are correct?

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Im not sure i understand' date=' how can we just subtract this frame?

Surely if this frame is moving from an outside observer the two masses are both accelerating toward each other. So if im at rest relative to the Earth, wouldn't i see the black hole accelerating towards me at >g?

Another way of looking at it: g for the black hole > g for the Earth. But how can you tell which is falling towards which since the claims from both frames are correct?[/quote']Lol, short answer; you can't.

Since there is no direct frame of refference, you cannot possibly say which point of view is more accurate.

In which case, everything pulls on everything else.

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Wow - I just had an epithany; I always wondered why it takes a constant acceleration to keep an object hovering above the ground, when it's so obvious where the extra energy goes; the Earth is pulled ever so slightly in the direction of the aircraft.

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Someone said earlier that acceleration due to gravity is not always constant because something might not be moving when in the presence of gravity. I thought that if you remain at the same distance from the center of gravity that it is always constant. The acceleration is constant but there are forces pushing upward (Newton's third law via the ground in most cases) counteract the force of gravity. Is this true? I'm not sure. kinda curious though.

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yeah, gravity is a constant pull, but other forces counter this force

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• 5 years later...

Hey all!

What about terminal velocity - doesn't that dictate that objects of different mass have different terminal velocity - thus fall once reached objects with differing masses would be falling at different speeds?

Her conclusion is perfectly correct!

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Hey all!

What about terminal velocity - doesn't that dictate that objects of different mass have different terminal velocity - thus fall once reached objects with differing masses would be falling at different speeds?

Her conclusion is perfectly correct!

Terminal velocity is due to friction and air resistance (or, more accurately, due to the restricting force of the fluid or gas they travel through).

In a VACUUM, items will fall at the same rate. In air, they will be affected by drag and air resistance.

~mooey

Cool!

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I like the intuitive argument that if it were true that heavier objects fall faster, then by combining a lighter object with a heavier one by a string, the total weight is larger than the heavier object alone, and thus the combined object should fall faster. But as the lighter object by itself would fall slower, it would, by the string, slow down the heavier object and so we have some sort of a fallacy.

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I like the intuitive argument that if it were true that heavier objects fall faster, then by combining a lighter object with a heavier one by a string, the total weight is larger than the heavier object alone, and thus the combined object should fall faster. But as the lighter object by itself would fall slower, it would, by the string, slow down the heavier object and so we have some sort of a fallacy.

And if you think about a parachute (which works pretty much as you described) it's also a good way to see how it doesn't really depend on mass as much as it does on air resistance.

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And if you think about a parachute (which works pretty much as you described) it's also a good way to see how it doesn't really depend on mass as much as it does on air resistance.

A cursory look at the parachute would tend to reinforce the idea, though — the light material falls slowly and the heavy one falls faster, and when tying them together the light one slows down the heavy one. You have to show show something else — like that there is no tension in the string when you tie two objects together.

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I guess there are two ways to look at this.

Resurrecting a thread from 2006 is old news, but then again, it was proved back in Galileo's time so a few more years hardly matters.

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oh dear, please ignoring air resistance (yes that includes "lighter than air" things) then they fall at the same rate.

You can argue against it as much as you want but you're wrong.

Nevertheless, the iron weight has more mass and thus more gravity, and therefor the planet and the iron will approach each other more rapidly than the planet and the feather.

Please note that the differences are miniscule, but they do exist.

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