MadSci Network: Physics

Re: do we move slower in space

Date: Fri Aug 14 01:35:51 1998
Posted By: Don Pettibone, Other (pls. specify below), Ph.D. in Applied Physics, Quadlux Inc.
Area of science: Physics
ID: 901811088.Ph

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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