Hard Light Productions Forums
Off-Topic Discussion => General Discussion => Topic started by: an0n on December 03, 2004, 11:59:54 pm
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If you had two blocks, identical in all dimensions but with one weighing 300kg and the other 3kg, the heavier block would fall faster.
The reason being that gravity is proportional to mass, so the gravitational field of the heavier block would be greater - and when combined with the pull of the Earth the overall downwards force would be greater than that between the Earth and the lighter block.
So all that crap about feathers and hammers is bull****.
I rest my mother****ing case.
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wrong - they fall at the same rate, in a vacuum
the only thing that causes objects to fall at different speeds in an atomsphere is drag
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With all things being relative, the combined gravitational pull between the Earth+H would be higher than Earth+L, thus it'd fall faster.
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If the blocks are the same dimension and different only in mass/density, they fall at the same speed.
I don't remember the physics equation, probably Kaz can help out in that respect, but they certainly do fall the same.
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Negligibly.
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technicallly yes, pratically no
unless one of the masses is a significant fraction of the planetary mass the difference in acceleration won't even be noticable
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And?
I wasn't concerned with degree, just that there was a difference.
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Well, duh. You kind of learn that your first week in any compotent physics class.
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the difference is SO slight, that the only way you could describe it is arbitrarily close to 0
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When you're talking about anything less than like, the moon, the gravity attraction is so small as to be negligible. Two objects of any reasonable size would fall at the same speed, or close enough for us to round it off.
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force = mass X acceleration
gravitational force is
G*(Mass(a) * mass(b))/distance_from_centers
as you can see the force of gravity is proportional to the mass of the objects in question. and acceleration is force/mass, therefore acceleration is constant for all objects
there isn't a degree (as far as anyone has ever been able to tell) it is zero.
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oh yeah!
sorry, im tired, bobbau is completely corect
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I had better be, I'm takeing a test on this crap in like a week
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The only way they'd fall at the same rate is if they were in exactly the same place and acting as a single body.
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So like, if the small guy grabbed hold on the big fat sumo wrestler to cushion his fall?
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nono an0n -- bobboau is correct, i could pick up my physics text and confirm that, and cite exactly from the pages
but im playing everquest
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You're forgetting about inertia. Yes, the gravitational force acting on one block is 100 times that of the other, but its resistance to motion is also 100 times greater.
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Originally posted by an0n
The only way they'd fall at the same rate is if they were in exactly the same place and acting as a single body.
I thought that was a given, if you drop the objects from diferent places there would be an infinitely small diference.
and also I was assumeing ridged body, as they are in block form and distortions from normal gravity would be nulled out by the nuclear forces holding the object together, gravity will act on each particle useing the above formula, each particle will fall at the same speed relitive to each other, the atoms closer to the earth would have an infinitely smaller amount of force than the ones away from it, but they would balence out to be equal as if gravity was acting on the sum of the particles mass on there center of mass of the particles. and sence you stated that they had identical shapes (though I am assumeing a uniform dencity) the centers of mass of the two objects would fall at the exact same speeds assumeing they were being droped on a planet like surface (ie not into a black hole) from the exact same place.
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Doesn't that mean everything always falls at 9.8m/s^2?
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nope :)
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**** it.
I'm too tired to do algebra. I'll argue my belief tomorrow.
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good, me too
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Wait, Kazan's playing Evercrack and he tells me I don't have a firm grip on reality? Does anyone else grasp the irony of this? :rolleyes::D :rolleyes: :rolleyes: :rolleyes:
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No. STFU.
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I don't have a problem, you have a problem! Don't tell me I'm playing too much, if anything I'm not playing enough! Only level 65 man, sixty freaking five! Now get out of my way, I neeedssss my Everquest.
:wtf: ;)
Though EQ2 is out at this point, which means another 4-5 years down the drain for tens of thousands of people. I've never understood the fascination, MMORPGs just can't hold my attention.
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i've only been playing it for two weeks :rolleyes:
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Then you're playing EQ2 then?
Rictor, I completely understand. MMORPGs have basically become cut and paste. After one party finishes a titanic battle with a dragon, gets their 1000000 XP, and leaves. The dragon regenerates for the next group. RPGs in and of themselves are cool, they tell some of the most epic storylines in gaming thanks to their length. But no matter what anybody says, ALL online games degenerate into mindless hack 'n slash because no matter what complex economic system the designers cooked up to allow you to make a living as a artisan or a herdsman or whatever, the easiest way to make cash for the goodies is to grab a weapon and kill some unsuspecting beasties ad-infinititem. Sure I know the devs release new story events into the world at random intervals. But they still suffer from the Alpha 1 syndrome. Everybody wants to be the hero and a world populated only with heroes is boring to me.
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no, im playing EQ1 - everyone says EQ2 SUCKS
i picked up EQ1 platinum for $30
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Ah, I get it now. You can change one object and still get the same accelerative force, but change the two and....
Right, I understand now. It's a 'between' force, not a 'from' force.
So with the small block the gravitational attraction between them is less, but the amount needed to move the smaller block is less.
That seems a pretty ****ing stupid way to run a universe.
But I thought the gravity curve was exponential, so the big block would move faster, even if you couldn't measure it.
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yes it is - but based upon distance, and inside and atmosphere like earths the net change in gravity between 0m and 10km is pretty neglible
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F=G * ([M1]*[M2]/d^2)
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Originally posted by an0n
Ah, I get it now. You can change one object and still get the same accelerative force, but change the two and....
Right, I understand now. It's a 'between' force, not a 'from' force.
Er - sort of. There's a whole bunch of "almost correct" answers in this thread; I'm going to try to straighten it out. Bobboau was correct, but didn't tell the whole story.
Force due to gravity = G * ([M1] * [M2] / r^2), as Bobboau (and Kazan) said. R is the radius between the two masses, measured from their centers. You can do this because gravity acts on all masses as though they were point masses - a single point in space at which all the mass is concentrated.
Now let's say that [M1] is the Earth and [M2] is the Moon. You want to measure the acceleration of the moon due to Earth's gravity, so using F = ma, F = [M2] * a becomes a = F / [M2].
If you write it out on paper, the [M2]s cancel each other out. So you're left with a = G * ([M1] / r^2). The Moon's mass has no effect. So if you took a baseball and the Moon and dropped them toward the Earth from exactly the same point in space, they would fall with exactly the same acceleration.
The only way you change the acceleration is by changing [M1] or r. So gravity changes over distance, as Kazan said. But this isn't really noticeable except with very large masses, such as black holes. Here, gravity changes so quickly that if you were falling feet-first toward the black hole, your feet would be accelerating several orders of magnitude faster than your head. Your body would disintegrate. :shaking:
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[size=1000]F=ma[/size]
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I prefer the...
mg = ma
g = a
method... :nervous:
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I've got a test on this next week, so this is indeed a usefull thread.
I don't entirely get Goob's "cancel eachother out" thingy, but AFAIK, the M1:M2 ratio doesn't change enough when earth is M1 and you're talking kilograms. 9.81m/s^2 is a rather rounded off number, btw. It changes a lot around the globe.
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Two objects will fall at the same speed, regardless of their mass/density/dimensions.
Why do they fall differently on Earth? Because air resistance slows one down, and not the other. They even tested this when Apollo went to the moon (I saw the video): They dropped a hammer and a feather, and both hit at the same time :)
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I prefer W=mad
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Originally posted by an0n
With all things being relative....
Uhm....no. That's the frelling point of Einstein, c (speed of light in vacuum) is constant, while everthing else is relative to it's respective inertial system.
So ....no cookie for you.
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Originally posted by Unknown Target
Two objects will fall at the same speed, regardless of their mass/density/dimensions.
an0n is talking about rediculusly small diferences, it's more of a retorical point than anything practical, infact the diferences in question are imposable to measure currently. if you have two objects of identical mass distribution the effects on all the particles will average out to them acting only on the center of mass, generaly speaking this is an incredably good aproximation for all objects. however the parts of you closer to the other mass will have an infintesemaly small diference in the force of gravity, an0n it nitpicking over technicalities here so we can't say it's exact, but it is infinitely close to exact as to be useable as if it were exact in practice (exept when we are dealing with black holes).
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Ice Cream=Yum? :nervous:
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Originally posted by Sandwich
Ice Cream=Yum? :nervous:
I LIKE those equations :D
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Originally posted by kasperl
I don't entirely get Goob's "cancel eachother out" thingy
Write it out on paper. It's much easier.
I'll try to diagram it here...M1 = Earth
M2 = Moon
F = G * M1 * M2
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2
r
F = M2 * a
a = F or a = F 1
-- * --
M2 M2
a = G * M1 * M2 1
----------- * --
2
r M2
Cancel out the M2s, and you get
a = G * M1
------
2
r So no matter what M2 is, it has no effect on the gravity.
if you have two objects of identical mass distribution the effects on all the particles will average out to them acting only on the center of mass, generaly speaking this is an incredably good aproximation for all objects.
It's more than an approximation... it's the exact same thing. You can treat everything as point masses, even black holes. When you calculate the gravity on each point within the mass, and integrate over the volume of the entire mass, everything cancels out. It gives exactly the same result as doing the conventional formula and treating it as a point mass.
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wich is what i said.
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Originally posted by Sandwich
Ice Cream=Yum? :nervous:
Sandwich=winnar
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Originally posted by Bobboau
wich is what i said.
The first part, yes. But the second part, no. It's not an approximation... it's the same thing. That's important to know.
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realy, even when you take into acount a diference in gravity that should tare any object apart, if you integrate it it will come out to be exact?
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Oh, crap. Now I'm not so sure.
*/me checks Wikipedia*
Aha. It does cancel out, but only for spherical masses.
http://en.wikipedia.org/wiki/Gravity
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HAHA!
I'm right again!
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Now I see, thanks Goob.
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HLP - where everyones a Physicist!
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Originally posted by Bobboau
HAHA!
I'm right again!
You're right to within any measurable difference from being totally right.