|MadSci Network: Physics|
Tom, I have wondered about this also. I looked around on NASA web sites and couldnít find anything that addressed your question. I have seen the golf shot you referred to and I agree that it looks like he is moving pretty slowly. However, I have also seen footage of the astronauts sort of bunny hopping across the lunar surface at alarmingly high speeds, so I donít think they have to move slowly. I can think of three effects that are probably causing this. The first is that the space suits are pretty bulky and restrict their movement a lot. Secondly, they are probably worried about falling down and getting a hole in their suit, so they are probably moving pretty cautiously most of the time. The third effect is due to the fact that they have to be careful because they are very strong for their weight in the low lunar gravity. Now you wouldnít think that this would be a problem, and it isnít in all cases, but at times it could be very awkward. This problem stems from the fact that frictional forces that keep your feet more or less stationary when you swing a bat or a golf club are proportional to your weight. If your weight is one sixth what is is on the earth, then the frictional forces that keep your boots in place are one sixth as great. Imagine what would happen if you were to take a big swing at a baseball while standing on slick ice. The lunar athlete faces a similar problem. If he or she were to jump straight up, they would do fine and they would go really high, but it would be tough to exert a lot of force that required frictional forces to help you maintain your footing, as many athletic moves do. In lunar basketball or football it would probably be impossible to make any really sharp cuts, by earth standards, unless you had world-class, or perhaps I should say lunar-class, spikes on your shoes. You would just slide and kick up a lot of lunar dust. As for your question about hitting a baseball on the moon: Suppose the spacesuit did not restrict you and you could somehow anchor your feet so sliding around would not be a problem. Then it is clear that you would be able to swing your bat at the same speed as you do on earth, though no faster as you are not working against gravity when you swing a bat. With the same bat speed , the ball would leave the bat at the same speed as it does on earth. Now you are cooking, because we no longer have air resistance to slow the ball down and with one-sixth less gravity the ball would go at least six times farther. Air resistance is a major factor, which also affects the optimum angle, so that the real distance might be more like 9 or 10 times farther than on earth. Since the longest measured major league home run is something like 570 feet, then on the moon it would be possible to hit a ball over a mile! Well, those are my thoughts on the subject. Looking forward to the time when the Olympics will rotate between sites on the Earth, Mars and the Moon, perhaps athletes will one day be able to show us what they can do in low gravity.
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