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Bicycling on the Moon

  1. Nov 7, 2009 #1
    Is a bicycle ridden with the Moon's gravity less likely to fall over than with Earth's?
     
  2. jcsd
  3. Nov 7, 2009 #2

    DaveC426913

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    This is a pretty ambiguous question. Let's start by assuming everything that can be made the same as on Earth, is the same. Normal flat, hard surface, breathable environment eliminating need for bulky spacesuit, etc...

    One major thing that will change is the rate at which the bike will fall. The astronaut's reactions as well as mass don't change, so it should be quite a bit easier for him to keep his balance, and/or re-attain his balance if he loses it.
     
  4. Nov 7, 2009 #3

    Danger

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    That's a cool question. Both it and Dave's answer triggered a thought. Once a lunar colony is established, bikes might be a pretty effective method of transportation. They would get rid of that weird hopping motion that the Apollo astronauts found most convenient for getting around. I'm thinking mainly of indoors, but slimline spacesuits and packed-down pathways might make them practical for surface use as well.
     
  5. Nov 7, 2009 #4

    DaveC426913

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    Well, as to how efficient it is, that's another question.

    I suspect that it would be quite difficult to get any appreciable speed, as well as difficult to turn. Both will tend to be more efficient when in higher gravity for the very same reasons that walking and running are.
     
  6. Nov 7, 2009 #5
    The answer is no. I don't see how the question is so ambiguous. Falling when riding a bicycle has nothing to do with the gravitational field that you are in. Instead, it has to do with the center of gravity of the bicycle-rider combination. Granted the fall would happen more slowly, giving you more time to react, and the impact would probably not be as great.
     
  7. Nov 8, 2009 #6
    Thank you for helping me refine my question. I was trying to compare the bicycle wheels' precession with the gravity of the two environments. I guess the first is a function of the bicycle velocity, and the second a function of the celestial body's radius and mass. Neither are directly related but both affect the rate of sideways fall for the bicycle.
     
  8. Nov 8, 2009 #7

    DaveC426913

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    Don't be silly. Of course it does.

    Do you think it would be the same of your were on Deimos, where g is less than 1/10,000th of Earth's?
    Or in interstellar space where grasvity is effectively zero?

    The Moon is simply on a scale between Earth and zero.
     
  9. Nov 8, 2009 #8

    Danger

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    I see where you're coming from. I was not, however, thinking in terms of speed. Rather, I was thinking that a bike would 'smooth out' the effort. It does so here on Earth, but the type of hopping done by the astronauts seems to be even more cumbersome than walking; hence, the difference would be magnified. The issue of turning didn't occur to me, and I don't know exactly how it would affect things. The main thing that I was thinking of was orderly ground-bound traffic rather than a horde of people bouncing around in constant collision.
    I should clarify that I'm thinking of a large colony, not a minimal base—something on the order of a small city.
    Truth be told, I really think that things like Segways and artificial wings will be the actual methods used.
     
  10. Nov 8, 2009 #9
    Well, Dave, you can't really fall in zero gravity can you?
     
  11. Nov 8, 2009 #10

    DaveC426913

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    Precisely. So you will agree that the gravitational field you are in (even if it is zero) must definitely be considered in the answer.
     
  12. Nov 8, 2009 #11

    Danger

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    Dave did say 'effectively zero', which is different than 'zero'. There's always some degree of microgravity, in which case you will still fall. It will take one horrendously long time, though.

    edit: Ah, you sneaked in on me again, Dave.
     
  13. Nov 8, 2009 #12
    You may not be able to exert as much power on the pedals in low gravity. If you had good traction you would be more likely to "pop a wheelie", or just skid your wheels. Just as you could not put all your power into swinging sledge hammer like here on earth, because your feet would not be planted securely on the ground.
     
  14. Nov 8, 2009 #13

    DaveC426913

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    It doesn't matter if it's nearly zero or theoretically exactly zero (which cannot occur). Simply put: the gravitational field is most definitely relevant.

    For example (to state it once again), if the gravitational field you are in is zero to an arbitrary number of decimal places, then your fall will definitely be different than if you were on Earth (by, say, not occurring).
     
    Last edited: Nov 8, 2009
  15. Nov 8, 2009 #14

    Danger

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    Good point, Leon. I don't actually think that you'd be any more likely to cat-walk or spin out, for the very reason of your first statement. You will have only 1/6th of the weight to apply to the pedals. Hmmm... I suppose that you could brace yourself downward with the handlebars, and thus apply more force. Hmmm...
     
  16. Nov 8, 2009 #15

    Danger

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    I completely agree with you, Dave, and I apologize if it seemed otherwise. It was merely my intention to point out that the universe doesn't contain any areas of actual zero gravity.
     
  17. Nov 8, 2009 #16

    DaveC426913

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    Not at all. And I just wanted to clarify that, while your fact is true, the answer to the OP's question does not depend on it being true.
     
  18. Nov 8, 2009 #17

    Danger

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    Quite right. :smile:
     
  19. Nov 8, 2009 #18
    Could'nt you theorize that there are moving points in space that contain zero gravity ?? - like a certain point between the earth and the sun. Few years ago I did sums to work out that point - but then forgot that it would be in orbit - so I would need some fancy calculus to get a final answer
     
  20. Nov 8, 2009 #19

    Danger

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    You could certainly have a moving point at which the gravitational fields of the Earth and the Sun cancel out; in fact, there has to be one. But that doesn't factor in the influence of every other body in the universe, each of which contributes in some degree.
     
  21. Nov 8, 2009 #20
    True you are Danger. My apologies for not picking up the definition earlier in the thread about the difference between Zero and effective zero.
     
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