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Post by Moon Man on Nov 16, 2005 12:50:35 GMT -4
Jason, I have another general question and I hope you don't mind if I post it in this thread.
Lets say you took a fully inflated basketball to the moon. What would happen to it..?
Would it explode..?
Would it deflate..?
Also, would a rock or, say, a round baseball roll down a hill on the moon..?
And assume no one has rolled it down the hill, imagine just placing it at the top of the hill.
I'm assuming the answer is yes after reading your answer regarding the rover descending a hill, but I had to ask because the rover example was already in motion.
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Post by LunarOrbit on Nov 16, 2005 13:17:27 GMT -4
Lets say you took a fully inflated basketball to the moon. What would happen to it..? Would it explode..? Would it deflate..? Only if the basketball couldn't handle the change in pressure. I imagine air would quickly leak through the little hole used to inflate it, but I'm not sure. Some inflatable objects were used on the moon... most obviously the spacesuits. But there were inflatable tires on a cart that the astronauts used on some missions. The rock would need some kind of nudge to get going. Objects at rest tend to remain at rest unless acted upon by an outside force.
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JMV
Venus
Posts: 41
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Post by JMV on Nov 16, 2005 13:34:00 GMT -4
Lets say you took a fully inflated basketball to the moon. What would happen to it..? Would it explode..? Would it deflate..? Only if the basketball couldn't handle the change in pressure. I imagine air would quickly leak through the little hole used to inflate it, but I'm not sure. Some inflatable objects were used on the moon... most obviously the spacesuits. But there were inflatable tires on a cart that the astronauts used on some missions. The rock would need some kind of nudge to get going. Objects at rest tend to remain at rest unless acted upon by an outside force. But if the ball was placed on a slope and if the ground was hard and smooth enough, it would start rolling down without a nudge. That's because the normal force supporting the ball on the ground would have a slight horizontal component.
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Post by nomuse on Nov 16, 2005 13:40:51 GMT -4
Did some quick research. I see a standard basketball can be inflated to at least 12 psi without exploding (that's 12 psi overpressure). Bounce is dependent on overpressure; inflated at zero psi it is still round, but doesn't bounce. Sea level is 14.7 psi. So it would be possible to to bring a basketball into vacuum without it exploding -- and it might just be possible for one inflated to playable pressure to still survive exposure. (My guess is, also, based on similar failure modes, that the inflation valve would blow out before the cover ripped).
The NBA standard cover is a "micro-fibre composite leather" similar to patent leather -- cheaper balls are composite rubber or rubber. Some have internal butyl bladders as well. I suspect most of these compounds are fair insulators, become brittle when cold, outgas in vacuum, and are also changed by strong UV radiation. The long-term prospects for our basketball are not good. If it were left out in the sun my guess is that the dark pebbled matt finish would be a decent absorber of solar energy and a poor radiator of infared; the ball would attempt to come to a much higher thermal equilibrium, thus raising the temperature inside until it exploded.
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Post by LunarOrbit on Nov 16, 2005 14:29:22 GMT -4
But if the ball was placed on a slope and if the ground was hard and smooth enough, it would start rolling down without a nudge. That's because the normal force supporting the ball on the ground would have a slight horizontal component. Right... I was thinking the ball was placed in a more or less level spot at the top of a hill, not on the slope.
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JMV
Venus
Posts: 41
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Post by JMV on Nov 16, 2005 15:07:10 GMT -4
But if the ball was placed on a slope and if the ground was hard and smooth enough, it would start rolling down without a nudge. That's because the normal force supporting the ball on the ground would have a slight horizontal component. Right... I was thinking the ball was placed in a more or less level spot at the top of a hill, not on the slope. Of course. I just wasn't sure what Moon Man meant with his question, so I thought it would be best to explain the slope situation too.
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Post by sts60 on Nov 16, 2005 15:21:40 GMT -4
Hope you don't mind a couple of general and somewhat random observations. Would it explode..?One of the sillier claims you will find made by some HBs is that the pneumatic LRV tires would have exploded on the Moon because they were placed in a vacuum. But there are two problems with this claim: 1. There is nothing special about a vacuum that makes tires explode. From an inflation standpoint, it's just an external pressure that's gone to zero, rather than 14.7 psi average at sea level. Put another way, it's like inflating the tires on your car to 50 psi instead of the 35 psi rating. But heavy truck tires are rated at upwards of 110 psi; clearly, tires can be made to operate at fairly large pressure differentials. Moreover, what happens when a large jet, with a couple of hundred psi in its tires, goes up to cruising altitude, where the air pressure is about 2 psi? Or the Shuttle goes into orbit, where its tires are in a vacuum? Nothing, because they're designed with the relatively small pressure differential increase in mind. This article talks about aircraft tires. SR-71 tires, for example, are inflated to 400 psi, but the air pressure at operational altitudes is less than 1/2 psi. 2. The LRV didn't have pneumatic tires. Only trainer models used on Earth did. But such is the attention to detail you will find at a typical Apollo "hoax" site. Also, would a rock or, say, a round baseball roll down a hill on the moon..?Sure, why not? It just wouldn't accelerate as fast as on Earth. Gravity pulls things downward wherever you are. Come to think of it, if you put a baseball on the side of a hill on the bottom of a deep sea trench, where the pressure is enormously greater than that of the air we breathe, it would also roll downhill.
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Post by Moon Man on Nov 16, 2005 15:34:32 GMT -4
WoW! I was just reading the link you provided on the distance the rover could travel. I was never aware that the astronauts had to stand up inside the lunar lander for the entire mission, unless they were going to sleep, as their were no seats inside the module. Therefore, Armstrong and Buzz stood for their entire mission since they never spent a night on the moon. Interesting.
Also, does anyone have a link showing the greatest distance the rover travel from the lander on each mission..? A moon walk timeline of where they were at each minute of the moon walk..?
And should I start a general Apollo question thread or is it okay if I continue to ask general questions in this thread..?
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Post by mushiwulf on Nov 16, 2005 15:42:20 GMT -4
When you say, "They never spent a night on the moon," it leads me to think you don't understand how long the lunar day is, still. In either case the astronauts could sit in the lander. I am not sure if both could sit at the same time though.
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Post by Moon Man on Nov 16, 2005 15:47:38 GMT -4
When you say, "They never spent a night on the moon," it leads me to think you don't understand how long the lunar day is, still. In either case the astronauts could sit in the lander. I am not sure if both could sit at the same time though. I know the lunar day is 28 days. When I say a night I am referring to our time. And according to the link I read there was no seats and no where to sit. They had hammocks to sleep on. Read the LM cabin. www.hq.nasa.gov/office/pao/History/alsj/apollo.engin.html
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Post by mushiwulf on Nov 16, 2005 15:50:21 GMT -4
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Post by mushiwulf on Nov 16, 2005 15:55:57 GMT -4
Also, I believe that Apollo 11 had an extrememly short mission profile. I am trying to browse through and see, but I get something like 2 hours and 31 minutes of EVA and a total of around 21 hours on the moon.
Apollo 17, for comparison, had 75 hours of surface time and 22 hours of EVA.
(source is wikipedia, so, caveat emptor)
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Post by scooter on Nov 16, 2005 19:39:06 GMT -4
www.geocities.com/bobandrepont/apollopdf.htm?200511scroll towards the bottom, the individual Apollo missions each have a section. Look under "Mission Report", every detail imaginable is there. Assuming you are indeed looking at these links at all. Also, standing in 1/6 g is significantly less difficult that here on Earth, it would be nice to weigh 30 lbs, frankly!! Dave
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Post by Moon Man on Nov 16, 2005 20:05:42 GMT -4
I'm reading them. Look what I just found. As you know, Armstrong had less then 30 seconds of fuel left before landing. The audio clip of his landing evidences this. Read this link at 113:01:15 and it says he had 50 seconds of fuel left. www.hq.nasa.gov/alsj/a17/a17.landing.htmlAlso, neil was on the surface of the moon for for at least 5 seconds before shutting the engine down, and despite the engine thrusting 3000 pounds of thust there is no crater.
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Post by mushiwulf on Nov 16, 2005 20:21:54 GMT -4
Well, it's a good thing he landed when he did then.
Was it thrusting 3000 pounds that whole time? (I really don't know).
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