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Post by brotherofthemoon on Aug 29, 2008 18:37:13 GMT -4
"Gravitational Drag" Yes folks, apparently gravity has much the same effects as air resistance does. Don't believe me? There's someone on the IMDB board for Mythbusters who keeps insisting that the LRV should have been capable of speeds of up to 90 miles per hour because the lack of "gravitational drag" on the Moon. Basically, anything should be capable of traveling six times faster on the Moon because it has one-sixth the surface gravity of the Earth. The poster's name is "Jon_Death," and the board is here (you might have to register to read it, though): us.imdb.com/title/tt0383126/board/threads/
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Post by Grand Lunar on Aug 29, 2008 19:06:09 GMT -4
Thankfully, I'm already a member of IMDb, so I can apply my knowledge in this situation.
What a hoot!
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Post by Czero 101 on Aug 29, 2008 19:18:50 GMT -4
Thankfully, I'm already a member of IMDb, so I can apply my knowledge in this situation. What a hoot! Ditto that... Cz
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raven
Jupiter
That ain't Earth, kiddies.
Posts: 509
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Post by raven on Aug 30, 2008 0:07:05 GMT -4
While gravity does have an effect on friction, things do tend to be more 'slippery' in lower gravity, I find it a little hard to believe it would be that great of an effect.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Aug 30, 2008 0:26:22 GMT -4
A vehicle experiences something called rolling resistance, which is the resistance the vehicle gives to rolling resulting from the deformation of its tires. Rolling resistance is the product of the coefficient of rolling resistance and the vehicle weight. Since weight is proportional to gravity, the rolling resistance is likewise proportional to gravity. The guy is, therefore, at least partly correct. Rolling resistance, however, is only a small part of the story. On Earth, air resistance is far greater than rolling resistance. Furthermore, a vehicle won't go any faster than its maximum motor RPMs and gearing will allow. The rover was engineered to go a certain speed -- it's not going to magically go six times faster by placing it on the Moon.
(By the why, rolling resistance is the reason under inflated tires are bad for your gas mileage.)
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Post by Data Cable on Aug 30, 2008 0:56:41 GMT -4
Without reading the linked thread (yet), this sounds suspiciously like "MrGuitarDeath," also from IMDb, who, among other howlers, asserted that the LRV should've had a top speed 6 times that of it's stated specs (apparently based on Earth-gravity tests), since the only limitation on an electric motor's maximum RPM would be friction due to gravity. [Edit: After looking, yeah, I'm pretty sure it's him. Here is the previous thread from IMDb, started by MrGuitarDeath. Every post of his in that thread has since been deleted, as has the account, but there's plenty of quoted text to get the gist. ]
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Post by JayUtah on Aug 30, 2008 11:30:52 GMT -4
I got the same feeling. Who wants to call him out?
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Post by PhantomWolf on Aug 30, 2008 16:49:14 GMT -4
Bags not, I had enough of him last time and I only posted about twice.
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Post by smlbstcbr on Aug 30, 2008 20:52:28 GMT -4
I don't want to imagine how this guy figures out how an F1 works, surely he'd say that a F1 on the moon would have entered in orbit after a good kick to the throtle. Actually, you meant "fluid resistance".
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Post by Ginnie on Aug 30, 2008 21:26:04 GMT -4
F1 - you mean the thruster?
You could almost lift off the whole Saturn V off the moon with one of those!
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Post by PhantomWolf on Aug 30, 2008 21:38:21 GMT -4
F1 - you mean the thruster? You could almost lift off the whole Saturn V off the moon with one of those! You likely could. It only took 5 to get the whole Saturn V to staging altitude, at 1/6 gravity 1 should be more than enough to get the entire Saturn V into a 50 nm orbit.
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Post by Czero 101 on Aug 30, 2008 23:37:53 GMT -4
F1 - you mean the thruster? I think he mean a Formula 1 race car. Going by "John Death's" theory, an F-1 racer should do about 1,200 Mph on the Moon Cz
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raven
Jupiter
That ain't Earth, kiddies.
Posts: 509
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Post by raven on Aug 31, 2008 3:04:28 GMT -4
I don't think it would get anywhere, as there is no air on the moon. And I do believe that an F1 gets its oxygen from the ambient atmosphere.
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Post by smlbstcbr on Aug 31, 2008 9:24:21 GMT -4
F1 - you mean the thruster? I think he mean a Formula 1 race car. Going by "John Death's" theory, an F-1 racer should do about 1,200 Mph on the Moon Cz Exactly Cz, I was talking about a Formula 1 race car.
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Post by gwiz on Aug 31, 2008 9:54:37 GMT -4
Did he check the ground clearance of a Formula 1 car? You'd be lucky to find anywhere on the moon where you could sit one on its wheels rather than its floor.
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