# Swimming on the Moon

1. Dec 18, 2003

### Borzorp

Anyone want to give a guy a helping hand? Just wondering if anyone understands how the physics of swimming would be different from swimming on the moon. My project is to adapt a sport (to help our spacemen of course) so that they can continue to work out while outside of our planet.
I play water polo at school and thought it would be easy enough to adapt to the moon since most of it is horizontal velocity. The ball seems easy enough to do, but the more I look into the physics of swimming, the more I wonder if the moon changes it a lot.

So, if there's anyone online in the forums who would please consider how and how much being on the moon vrs. earth would change swimming, please reply. BTW On the moon we can make a structure and fill it with air, but we still cannot remake gravity. So I'm thinking gravity will be the main variable. I know it will be much easier to tread, but what about water displacement and such when you're moving in a horizontal direction... will that change?

2. Dec 18, 2003

### HallsofIvy

Staff Emeritus
I think the lack of water would be the main problem!

3. Dec 18, 2003

### Borzorp

Hm... well, we could import the water from earth... and then fill a room with gases and then put the water into a pool... assuming that we could do that, how would the sport change?

4. Dec 18, 2003

### Chemicalsuperfreak

I think the most obvious difference is that you'd have much larger waves and splashes. And passing the ball would travel much further.

5. Dec 18, 2003

### Borzorp

I think that the larger waves and splashes could be balanced out by the fact that you would be able to tread higher, right? The force making the wave would be the same, so the force making you tread would still be high enough to get you over those waves...

But, I don't understand why playing water polo on the moon would make passing the ball much faster. Is there a horizontal component I'm overlooking? I thought the problem was alomst purely dealing w/ gravity (i'm supposed to look at everything, of course) So... if i'm missing something, what is it?

6. Dec 18, 2003

### NanoTech

This topic interests me, because it reminds me that we still have a long ways to go before experiments can be accomplished in outer space. With the construction of the new space station, these types of experiments (thermodynamic/motion of water) will be conducted in much deeper research. The factors of water with differences in gravity is the main topic of research I suppose for this project. But I can't even fathom there being any waves at all, since the reason we have waves on Earth is because of the moon travelling around us.

7. Dec 18, 2003

### Jupiter

You're right that it wouldn't go faster. But chemicalsuperfreak said it would go farther. This is true:
$$x_{max}=\frac{v_{0}sin2\theta}{g}$$
So decrease g and you increase the range.

8. Dec 18, 2003

### Borzorp

I'm thinking he's meaning waves from the pool... the force would be mainly from the people having very little to do with the moon.

9. Dec 18, 2003

### brum

Fb = pVg

Buoyant Force = (Density of water) (Volume displaced by person) (gravity constant)

p (rho) (density) stays the same
V stays the same
g decreases

Thus, the buoyant force (pushing up on you) decreases.

Your weight, however, decreases by the same factor.

(F = mg)
(Weight = mass * gravity constant)

Therefore, you would float just as high on the moon as you would on Earth.

10. Dec 18, 2003

### NanoTech

So the bonds of water would stay relatively the same when gravity is varied. In other words, the density of water is always the same no matter what amount of gravity is produced? Would the density of a ball be the same when travelling through a black hole?
And I wasn't talking about a pool in that specific idea(sorry forgot to mention that), I was refering to an ocean or lake.

11. Dec 18, 2003

### Integral

Staff Emeritus

Density is mass per unit volume, so yes, density is indepentent of gravity.
BLACK HOLE??? Where did that come from I thought we were on the Moon! this is an entirely different question, please keep it seperate.
Once again, I though we were talking about the moon, there are no rivers or lakes, if there were it would be no different from any other pool of water.

Is there any difference between swimming in a swimming pool and a (freshwater) lake?

12. Dec 18, 2003

### Achy47

I'm guessing that the bends would be much less common.

13. Dec 18, 2003

### Borzorp

haha thanks integral. You cleaned up the non helpful comments, but sadly didn't add any yourself! Argh, haha. This damn thing is due tomorrow... Now i've figured out that bouyant force + Weight balances you out in the water... but now, more specifically... when you start treading and a force to your feet... how the heck do you know how much force will be needed???

Fnet = (m)(a)

(m) (g) + Force Generated by Feet = (m) (a)

The Gravitational force is there, so it will in fact be different in both places, but how much different? How could you tell how much force will be generated by your feet? maybe just enough to overcome weight??

14. Dec 18, 2003

### Loren Booda

Are we dealing only with direct gravitational effects here?

15. Dec 18, 2003

### NanoTech

i'm talking about the waves produced by lakes/oceans and not swimming in them. i guess your right - the size of the wave is relative to the size of the body of water. hence, thats why ocean waves are so big. i know i'm getting off the subject here, but i'm guessing an oceans tides would be different on the moon(or any other planet) compared our earth's tides.

16. Dec 18, 2003

### Borzorp

LoL, who cares!!! this is due tomorrow... In a minute I'll post up what I have if anyone actually wants to help... damn, I feel retarded in physics.

17. Dec 18, 2003

### Integral

Staff Emeritus
I didn't add anything because I felt it was pretty well covered.

Could you put some personal effort into putting these pieces together?

You now know that you will float the same, buoyancy is relative density.

The force your feet exert on the water are not gravity dependent, the vertical opposition to those forces are gravity dependent.

It is not the general policy here that we do homework for people. You have been given a big portion of your answer, try to put some of it together yourself.

18. Dec 22, 2003

### Andthensome

How about moonwalking on water? Hmmm?

19. Dec 22, 2003

### Loren Booda

Would cavitation be appreciably affected?

20. Dec 22, 2003

### Achy47

Good 1

My guess is that impeller based pumps would not be affected (except for the priming stage).

But If you are talking about boat props...hmm.. good one.
My my wild guess would be yes, as the air on the surface of the water would have an easier time reaching the prop on average. Surface drive props (usually used for high performance apps) would probably be affected in a similar way.