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Post by PhantomWolf on Aug 24, 2005 10:08:43 GMT -4
On the length of stride thing, you also have to remember that people's legs don't miraculously grow longer in lower gravity. The length of the step of person has more to do with the length of their legs than it does the gravity they are in.
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Post by gwiz on Aug 24, 2005 10:28:56 GMT -4
On the length of stride thing, you also have to remember that people's legs don't miraculously grow longer in lower gravity. The length of the step of person has more to do with the length of their legs than it does the gravity they are in. Though with a lope, both feet off the ground at times, a lower gravity and longer off the surface at each step will give a greater stride length for a given speed.
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Post by JayUtah on Aug 24, 2005 12:27:18 GMT -4
The astronauts mentioned this specifically. They said that for long-distance or high-speed ambulation, the two-footed lope is best because it doesn't require holding one leg extended and the other flexed for an unnaturally long interval. It turns out the rhythm of connected human ambulation is closely tied to how fast you "fall" onto the forward foot. When that rate is changed, the brain must learn to time the steps all over again. This is made even more difficult, as you can imagine, by the restriction of the suit. And, of course, if legs were longer that would change things too.
But "stride" has little meaning in the lope. There are really two strides: the short one between the two foot contacts, and the long one comprising the bound. The lope minimized hip flexion while relying more upon knee flexion and extension. But more importantly, the bound generated additional height over a walk, leading to greater impact at landing. This impact force help flex the knee joint against the resistance of the suit, requiring less muscle effort to flex for the next departure.
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Post by Mr Gorsky on Aug 24, 2005 18:36:31 GMT -4
If all that stands between you and vacuum is a space suit, you're not going to risk a fall that damages it. A high jump in 1/6 g means a long time off the surface with no means to control your attitude and keep pointing head up/feet down. These factors combine to suggest that going for the maximum high jump is unwise. One of the continually baffling elements of hoax arguments is this theory that if we are capable of doing something, then it is somehow suspicious if we don't do it. My car can travel comfortably at (just ... only just) over 100mph. However, if I actually drive at that speed I run the risk of being pulled over and possibly losing my licence, so I choose to stick to the speed limits, where I am safe from prosecution. Nothing suspicious about my unwillingness to drive at my car's top speed, it is simply a sensible precaution. Likewise, the Apollo astronauts on the lunar surface ... As I understand it, a very strong reason for not jumping high was the tendency to topple over backwards, due to the added weight and position of the Personal Life Support System. In these circumstances jumping high, thereby running the risk of landing on your back and damaging the only thing keeping you alive, would be foolish. At best! Not jumping high is therefore not suspicious, just a sensible precaution.
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Post by jaydeehess on Aug 24, 2005 20:15:07 GMT -4
Another analogy concerning jumping on the Moon would be to get on a trampoline. An Olympic expert gets a lot of height and can do twists and moves that are quite fantastic. He (or she) isn't wearing a backpack, is wearing a highly flexible set of clothing and has spotters and mats all around the equipment in case of trouble, and finaly , they have had a LOT of practice!
Now if I get on a trampoline there is no way I am going to attempt the height that those people get! Even several Scotch would not give me the insane courage to do that. (I have fallen 8 feet and landed on my feet in 2 feet of fluffy snow and it hurt! )
Being in an airless enviroment with a heavy backpack(the weight would not be much but it would still have the same mass and therefore inertia), and knowing that if you fell your comrade up there with you is going to have some trouble helping you up AND if you actually sprain an ankle or worse the two of you are going to have a bitch of a time just getting you into the LEM not to mention that YOU will have caused the premature end of the mission.
No, it is not a mystery that they did not attempt much in the way of gymnastics on the Moon.
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Post by Mr Gorsky on Aug 25, 2005 9:12:02 GMT -4
But just imagine how high those trampolinists could go ...
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Post by Count Zero on Aug 25, 2005 12:30:03 GMT -4
But "stride" has little meaning in the lope. There are really two strides: the short one between the two foot contacts, and the long one comprising the bound. The lope minimized hip flexion while relying more upon knee flexion and extension. But more importantly, the bound generated additional height over a walk, leading to greater impact at landing. This impact force help flex the knee joint against the resistance of the suit, requiring less muscle effort to flex for the next departure. Here is an example of "bounding" and the hazards of "getting too much air-time*" over uneven ground. Nice example of ballistic dust in 1/6th G vacuum, btw. Note how Gene uses the spring action in the knee joints to get back up. Yes, I know it's not really 'air'-time; that's why I used quotes, you frelling nit-picker!
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Post by jaydeehess on Aug 25, 2005 18:44:29 GMT -4
But just imagine how high those trampolinists could go ... Assuming you constructed a large, high ceilinged, pressurized room and placed the trampoline in it the gymnist would theorectically be able to get much higher,,,, or would he? The force that the trampoline returns to the person is dependant on the amount of stretch the trampoline gets. That trampoline is going to get less stretch because the force on it from the person's weight will be 1/6th that it would be on Earth. So getting started will be more of a problem. Secondly it is going to take a lot of practice for the gymnast to get used to the changes in the speed at which things happen. This is a whole new world of experience. The good point is that if you do make a mistake you will have a little longer to react before you hit the ground.
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Post by Count Zero on Aug 25, 2005 20:01:25 GMT -4
This is a whole new world of experience. The good point is that if you do make a mistake you will have a little longer to react before you hit the ground. More likely you'll have more time to appreciate how painful your impact is going to be, and how stupid you were to try this move... Personally I liked Heinlein's idea from The Menace from Earth: Create/find a very large enclosed space on the Moon, pressurize it, then just strap on wings and fly around.
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