Faster than the speed of gravity...I don't think so.

Phonedave

Phonedave

Well-Known Member
musketeer said:
Not quite. Gravity is not a speed, nor is it an acceleration, it is a force. The force accelerates an object at a certain rate, but the acceleration due to gravity isn't constant. For all practical purposes on the surface of the earth, it is as close to constant as we need it to be. But the farther you get from earth's surface, the less the force becomes. And it isn't just going away (or up) from the surface of the earth, but going down also. If you were to go away from the surface of the earth (up), the foce decreases because the distance increases. If you were to dig a tunnel to the center of the earth, as you go down, the force decreases because the mass of the earth pulling you towards the center decreases.

Also, there isn't really a cap for an object falling in free fall, unless there is some medium that it has to go through other than a vacuum. Terminal velocity is just the velocity where the force of gravity equals the drag associated with the velocity. Drag is proportional to velocity (might be velocity squared), so when that velocity is reached, no more acceleration occurs unless gravity increases (which technically it does as you approach the surface), or the drag of the object changes (becomes more aerodynamic, etc)

By the way, if you were to dig a tunnel all the way to the other side of the earth, and if you could evacuate all the air from the tunnel, and jumped in, it would take 42 minutes to reach the other side, and when you passed through the center, you'd be traveling around 11 miles per second.

Even more interesting is that if you dug the tunnel from any one point to any other point (the tunnel has to be perfectly straight and a vacuum), say New York to London, gravity would pull you through the tunnel (slower of course because you aren't going straight down), and it would take 42 minutes.

No matter where you start or end, it would take 42 minutes. So theoretically, you can travel from any point on earth to any other point in 42 minutes with only gravity doing the work.
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I think the OP was being even more literal (maybe) than that.

He was taking the "speed of gravity" to be "the speed at which a gravitational field propigates" which is (AFAIK) the speed of light.

In other words. Say you were standing there all nice and quitet, and then *poof* a mass was introduced into the system at a distance x away. You would not feel the gravitational "pull" (yes, I know, pull is not the correct term, and it is also a mutual force, you on it and it on you) instantaiously, but instead a short time later, due to the fact that the gravational field has to propigate a distance x to reach you..

What this has to do with the operation of ToT is beyond me.

Of course i close my eyes so I cant see if the car is going up or down, therefor its in both places at once (all apoligies to Mr. Schrodinger and his feline)


-dave
 
Phonedave

Phonedave

Well-Known Member
Master__Gracey said:
Guilty as charged. Astrophysicist :wave:
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Civil Engineering and I have the degrees to proove it, and I currently work in telecom and hold an Engineering title there. However all I really do is budgets, contracts, and project management :lookaroun (all much faster than the speed of gravity too)

-dave
 
Montyboy

Montyboy

New Member
I'll raise my hand

musketeer, nice post. In this case the force of gravity should be treated as an acceleration because one mass is negligible.
Where would you place it in Newton's equation F=ma?

Hey Dave - Mechanical engineers build weapons. Civil engineers build targets.
 
EpcoTim

EpcoTim

Well-Known Member
Gravity isn't actually a speed, it's a force, so technically it would be faster than gravity, seeing as gravity isn't physically moving. It's a force that simply causes the movement.

a. The natural force of attraction exerted by a celestial body, such as Earth, upon objects at or near its surface, tending to draw them toward the center of the body.
b. The natural force of attraction between any two massive bodies, which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
c. Gravitation.


I'm probably way late on this
 
sarabi

sarabi

New Member
devoy1701 said:
I didn't realize that physics majors spelt acceleration different than the rest of us. :shrug:
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Didn't realize non physics majors spelled "spelled" differently than the rest of us. :)

Sorry to offend... no time to spell check. Just because I can do math doesn't mean I can spell.

And no, not a physicist... just a major. Double majored and did not pursue either field (ha!). But yeah, I'm pretty sure gravity as we are talking about it here "g" is an acceleration (did I spell that right?) not a force.

And the only reason I got technical was because the OP wonders if the claim made by the ride is possible. And the answer is yes and no. No, there is "speed of gravity" but assuming they mean "rate of gravity", then yes. Knowing that laymen call the "rate of gravity" the "speed of gravity", I'm going to say the ride makes no false claims.
 
wdwfan100

wdwfan100

Active Member
sarabi said:
Didn't realize non physics majors spelled "spelled" differently than the rest of us. :)

Sorry to offend... no time to spell check. Just because I can do math doesn't mean I can spell.

And no, not a physicist... just a major. Double majored and did not pursue either field (ha!). But yeah, I'm pretty sure gravity as we are talking about it here "g" is an acceleration (did I spell that right?) not a force.

And the only reason I got technical was because the OP wonders if the claim made by the ride is possible. And the answer is yes and no. No, there is "speed of gravity" but assuming they mean "rate of gravity", then yes. Knowing that laymen call the "rate of gravity" the "speed of gravity", I'm going to say the ride makes no false claims.
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I believe that is good enough for reasonable doubt your Honor. I move for a dismissal. :lol:
 
Montyboy

Montyboy

New Member
sarabi said:
Didn't realize non physics majors spelled "spelled" differently than the rest of us. :)

Sorry to offend... no time to spell check. Just because I can do math doesn't mean I can spell.

And no, not a physicist... just a major. Double majored and did not pursue either field (ha!). But yeah, I'm pretty sure gravity as we are talking about it here "g" is an acceleration (did I spell that right?) not a force.

And the only reason I got technical was because the OP wonders if the claim made by the ride is possible. And the answer is yes and no. No, there is "speed of gravity" but assuming they mean "rate of gravity", then yes. Knowing that laymen call the "rate of gravity" the "speed of gravity", I'm going to say the ride makes no false claims.
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Wow, I before reading this, I thought I knew physics! What field did you end up in?
 
Phonedave

Phonedave

Well-Known Member
Montyboy said:
Hey Dave - Mechanical engineers build weapons. Civil engineers build targets.
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Oooo, thems fighting words. In college the ME's would go into a lab and do some flow rate deal, or work with small materials samples. All clean and dainty. Then they would see us come out of lab in work boots and hard hats after playing with the the gantry crane, cement mixers, and environmental chambers.

ME's did have a better group of "soft personnel" though :animwink:

-dave
 
SeaBreeze

SeaBreeze

New Member
Phonedave said:
Oooo, thems fighting words. In college the ME's would go into a lab and do some flow rate deal, or work with small materials samples. All clean and dainty. Then they would see us come out of lab in work boots and hard hats after playing with the the gantry crane, cement mixers, and environmental chambers.

ME's did have a better group of "soft personnel" though :animwink:

-dave
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Are you sure you want to start battling MEs? I think you might be outnumbered :animwink:

And I'd just like to point out that after a day of working in my lab, I rarely come out of there clean and dainty. There's a reason I have to wear a respirator, gloves and jacket :lol:
 

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