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Question about gravity

  1. Feb 10, 2010 #1
    Hello everyone, first of all i would like to appolagize for my not so good english, so if you please try to answer to my question as simple as possible so i will understand.
    i would also like to add im not studying physics, never have all thought i might will some time. since its a subject that interest me.
    ok so my question is this
    A.theoreticly, if a man is on a small planet as small as ping pong ball, and since this planet is small this guy is very close to the gravity center of the planet, and lets say this planet have twice of the gavity force of earth core, doesnt matter numbers right now. would that man body will be twice heavier? (if he weight 80 kg he will weight 160?)
    my second question is this..
    B.a Carousel is spinning in a very high speed,(the fast it spins the more gravity force it preduce?)
    and lets say a man is standing in the middle of the Carousel at the part that doesnt spin, will the gravity force effect on him too? or for him to feel the gravity the Carousel needs to spin in a very unusuall speed
    My 3rd question is this
    If there will be a mission of NASA to send people to other planet with twice or three times the gravity force of earth can they build a certin chamber the will simulate that force? like the oppsite of no gravity force they already have

    if anyone can leave answers here as simple yet detailed answers here or to leave me a message or email me to Shayohayon@hotmail.com i couldnt thank you enough!
    these questions had troubled my mind for alot of time.. i really wish to know more. TY
  2. jcsd
  3. Feb 10, 2010 #2
    1. First of all, you must distinguish mass, which is a property of a body/particle, and weight which is actually a force.
    If a man is on a planet which has twice of the "gravity force of earth", then he will feel he weighs more, but he'll not gain more mass.
    The assumption that the man is closer to the core is not really needed once you've stated he feels more force, but generally gravity is a function of the distance (its proportional to the distance inversed and squared).

    2. A carousel doesn't produce a gravity force (actually it does, but it is very small and I assume you haven't meant that kind of force), but a rotating body will feel a force we call a centrifugal force, which acts outwards. The centrifugal force is a function of how fast is spins, which is called the angular velocity, and usually denoted w, so
    So you see the force does grows as the angular velocity grows, but it also grows as the distance from the pivot grows.
    So when a man stands on the pivot, r=0, and therefore he will feel no force (approximately, of course a man has dimensions, so part of him will be at a distance of the pivot. Another realistic reason why he feels no force is due to friction).

    3. Well I believe there are many creative ways to simulate a force.
    One was stated in question 2, although it's quite weird to rotate a room, and in what direction would you rotate it?

    You can also feel an "imaginary" force acting on you while in the elevator- when the elevator accelerates upwards, you'll feel a bigger g force acting on you towards the floor, which will make you feel that you weigh more than usually.
    When an elevator accelerates downwards you will feel exactly the opposite.
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