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Thread: Acceleration

  1. #1 Acceleration 
    Forum Masters Degree thyristor's Avatar
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    In the movie "2001 a spacey odyssey" there's some kind of rotating wheel to a space base. The rotation of the wheel makes it's passengers feel like they were on the earth because there's a force pulling them to the floor. I just wonder, what correlation is there, mathematically, between the diametre of the ring, its rpm and the force generated that pulls its passengers to the floor?


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    It's the formula for centripetal force

    F=m*v^2/R

    Where the velocity v = 2*(pi)*R*frequency in rpm


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    The above formula by Harold is quite correct, but it may be easier for you to visualize the results by considering centrifugal force. With this treatment, the force a person would experience depends on (angular velocity)-squared times R, in which R is your distance from the center of the wheel.

    Now it is easier to see that a structure that spins faster creates stronger artificial gravity, and the effect is greater when you are closer to the rim than when you are near the center. At the center itself (R=0) there is no force at all.

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    Centrifugal force is what you would consider in the frame of reference of a passenger rotating with the wheel. Since the reference frame is rotating, it is accelerating; thus it is a noninertial frame, and centrifugal force manifests itself as a ‚Äúfictitious force‚ÄĚ in it.

    When you are outside the wheel (and not rotating with it), you would see the force on each passenger as a centripetal force instead.
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    Correct.

    For revolution of a body around a fixed axis, the net force on the body must act toward the axis at the centre of the circular path of the body. In the movie, this is provided by the normal reaction force provided by the floor on the people.
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    Quote Originally Posted by PritishKamat
    Correct.

    For revolution of a body around a fixed axis, the net force on the body must act toward the axis at the centre of the circular path of the body. In the movie, this is provided by the normal reaction force provided by the floor on the people.

    If you were spun in a large round space station. When you start to move, your body will try to move in a straight line.
    Since the moving floor of the space station will get in your way. It will apply force to your feet.

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    Actually, you're wrong here. Since all the people rotate with the room, they are at rest with respect to it and won't feel it slipping away from beneath their feet. Moreover, the rotational motion of the room exerts a "pseudo force" on the people (which pushes them away from the axis of rotation).

    If the room is a right cylinder, with the axis passing through the centre, and the people walk on its walls (inner curved surface), the people will feel a force tugging at them 'downwards' and might be used to simulate gravity by setting some particular angular speed.
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    Quote Originally Posted by PritishKamat
    Actually, you're wrong here. Since all the people rotate with the room, they are at rest with respect to it and won't feel it slipping away from beneath their feet. Moreover, the rotational motion of the room exerts a "pseudo force" on the people (which pushes them away from the axis of rotation).

    If the room is a right cylinder, with the axis passing through the centre, and the people walk on its walls (inner curved surface), the people will feel a force tugging at them 'downwards' and might be used to simulate gravity by setting some particular angular speed.
    The floor of the space station will move upwards, into the objects natural straight line path, their body is trying to move in.

    And cause pressure upon their feet.

    As he moves it is as if he is hitting a curved circular ramp. I am working on a video.



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    Of course the floor wouldn't be flat! You would feel the same as if you were walking on a curved ramp, but still, it wont be the same, since, in space, in a rotating cylinder, the force tugging on you will always be perpendicular to the tangent to the surface you are walking on at the point of your position (just like walking on flat ground on earth).

    But, if you are walking on a ramp on earth, the force tugging on you is in one direction only (towards center of the earth), so, you need a force of friction to counter the force of gravity and take you upwards.

    I have made pictures depicting this, but I have them as .jpg and I don't know how to upload them
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    I use tinypic.com.
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    And you just copy + paste it?
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    Quote Originally Posted by serpicojr
    I use tinypic.com.
    Thanks for that :wink:
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

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    Quote Originally Posted by PritishKamat
    Of course the floor wouldn't be flat! You would feel the same as if you were walking on a curved ramp, but still, it wont be the same, since, in space, in a rotating cylinder, the force tugging on you will always be perpendicular to the tangent to the surface you are walking on at the point of your position (just like walking on flat ground on earth).

    But, if you are walking on a ramp on earth, the force tugging on you is in one direction only (towards center of the earth), so, you need a force of friction to counter the force of gravity and take you upwards.

    I have made pictures depicting this, but I have them as .jpg and I don't know how to upload them
    The floor is flat, the path of the floor is a curved circular path. This causes the effect of being on a skate board and hitting a curved ramp. It puts a lot of pressure upon you.

    I know I have hit arced ramps on snow skis, and they send you almost straight up. Busted my bumpkin one day. Ha-ha. There were some other individuals that had just hit it. And they all offered me shot of brandy. I took it and I don't drink.


    There is no force tugging on you. There is a force tangent to the space station floor, moving you away from the wheel. As the floor blocks this straight path, pressure is put against the floor, and the floor puts pressure against the person standing on the floor.

    The formula to figure out the force, would be velocity of the circumference traveled per second, and the deviation from a straight path, per second, caused by the radius. Then you could calculate how much force is being applied.

    In other words if the circular path of the flat floor of the space station blocked you to create a deflection of your straight path by four inches a second, that could be turned into measurable force. Or horse power. Or G'S.


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    Here is a video I made. Showing a graphical illustration of what takes place.

    http://www.Rockwelder.com/Flash/mrbi...mrbill8x6.html

    The only thing that is not real, is that if the space station started to turn, he would not just stand there and take off with it, it would put Mr. Bill into a cartwheel spin.
    There would be no reason for him to stick to the floor. Or suddenly want to move with the space station. He would be weightless before the station started to turn. And would just leave the floor. He may not even obtain any artificial gravity until he bounced enough times and picked up velocity.

    Therefore he is wearing magnetic boots in the movie. Ha-ha.


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    I wont bother answering you any more. You're just wasting everyone's time.
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    To be fair i can see williams point.... but in the same light, everyone else is completely right

    In reference to william: This is not good logic william. Example, Standing on earth You have a ball on a string and spin it above your head, you release the string and the object will move at a tangent to its respective path and parabolically perpendicular to the centre of gravity.

    Repeat the same experiment on said space station, it will have the same effect, the tangent at which the ball could be released is random... but it will take a parabolic path perpendicular to the spin of the space station, the gravitational effect is no different as if you were on earth assuming g=9.81 in this case...

    A ball on a string does not "Cartwheel" william, the string acts as what would be the inner surface of the station in comparrison. and besides, your assuming there is already gravity in place in order to cause a second external force pulling the person in the opposite direction to the motion or in one constant direction, which isnt the direction of motion.

    The only real difference between the artificial gravity and the False gravity is the fact that one is real, one is artificial.... They both serve the same purpose.

    In reference to everyone else:
    I dont think you needed any of the explaination above at all, as long winded and dumbed down as it was hehe.

    You are all absoloutly correct, im no genius, but im not stupid enough to assume that in the absence of gravity one external force would induce another in the opposite direction which is greater than the current force :S No Gravity, No "cartwheeling".
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    Quote Originally Posted by Alc
    In reference to everyone else:
    I dont think you needed any of the explaination above at all, as long winded and dumbed down as it was hehe.
    Actually, it's a good illustration of Einstein's equivalence principle - the basis of the General Theory of Relativity.

    And I agree with you - William's first post in this topic was pretty relevant and kind of accurate (it's just a way of representing what's going on - and even Newton is said to have imagined the moon constantly falling towards the earth, so a floor constantly rising to meet you makes sense too), and far from as outre as his posts tend to be.
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    Quote Originally Posted by PritishKamat
    I wont bother answering you any more. You're just wasting everyone's time.


    What did I do wrong? What is incorrect? I think you owe me that.


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    Quote Originally Posted by Alc
    To be fair i can see williams point.... but in the same light, everyone else is completely right

    In reference to william: This is not good logic william. Example, Standing on earth You have a ball on a string and spin it above your head, you release the string and the object will move at a tangent to its respective path and parabolically perpendicular to the centre of gravity.

    Repeat the same experiment on said space station, it will have the same effect, the tangent at which the ball could be released is random... but it will take a parabolic path perpendicular to the spin of the space station, the gravitational effect is no different as if you were on earth assuming g=9.81 in this case...

    A ball on a string does not "Cartwheel" william, the string acts as what would be the inner surface of the station in comparrison. and besides, your assuming there is already gravity in place in order to cause a second external force pulling the person in the opposite direction to the motion or in one constant direction, which isnt the direction of motion.

    The only real difference between the artificial gravity and the False gravity is the fact that one is real, one is artificial.... They both serve the same purpose.

    In reference to everyone else:
    I dont think you needed any of the explaination above at all, as long winded and dumbed down as it was hehe.

    You are all absoloutly correct, im no genius, but im not stupid enough to assume that in the absence of gravity one external force would induce another in the opposite direction which is greater than the current force :S No Gravity, No "cartwheeling".

    Well if you do not commit a poor scientific variable, when you try to start your ball on a string, you will just wrap the string around your body until it tightens up around you and then starts to spin the ball. After the ball has moved up to your body.

    You would have to throw the ball out to the end of its leash to start it off.

    On a space station, there is nothing holding you to the floor. So as the space station goes to move, it will just spin you and push you away from the floor before you gain velocity.

    Remember you will be weightless, nothing is going to connect you to the floor. You would just bounce around until you eventually gained velocity. That would cause you to maintain a constant collision with the floor of the space station.

    That is why I said he is wearing magnetic shoes until the space station gets to speed. Ha-ha.

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    Alc
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    I don't think you quite see the point.....

    If you pul a rug from underneath someone on earth, there is huge frictional force, which causes a foce in the opposite direction. causing the object to topple about its centre of gravity.

    Now in a weightless space, there is no gravity, and imagine you in a stationary shuttle which is not spinning and has no artificial gravity what so ever.... Friction would still exist, and in this case yes would induce a turning force on the object, given the space was adequate.....

    In the spinning space station, it realy is a different story, the velocity of what ever is on the surface is constantly changing, accelerating towards the centre as it turns, pulling a rug from under someone here would be similar to earth, it would cause the object to tip over not roll... purely because "artificial gravity" is present.....

    Now i see you keep making reference to the fact that it wouldnt be practical and the guy would need to be wearing some sort of magnetic boots. I can kinda see you point... because before it begins to spin there is no gravity, but you would NEVER roll in this case. unless you were dead centre in the cylinder you would start turning as the object did. your frame of reference would not change at this point as there is no gravity before hand you would stay at the same point inside the cylinder, but as it turned you would turn with it, which would pull you to the edge, even if not on your feet.... you would not roll, theres nothing to say that there will be a second set of completely independant forces acting upon the person inside.
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    If you are standing where Mr. Bill in the movie is standing, and you maintain that posture. Stay relatively stiff. As the space station starts off. The left leg of the Mr. Bill or whom ever, will be jammed into the floor at first, due to the geometric shape of his stance. And he will indeed cartwheel and lift off the floor. With little actual acceleration to create artificial gravity.

    Only if he was wearing magnetic boots or was stuck in bubble gum will he take off nicely with the space station.


    It would still be exactly as if you pulled the carpet out from under him. Only better.



    Do you understand that you cannot move in an area until you become a diode and harness ambient radiation. So that you can move.

    The reason why Mr. Bill will cartwheel is because, as soon as the space station moves. His right foot will lift off the ground. Spinning him ever so slightly. Placing all the pressure on the left foot. Why? Because it is easier to spin him then to accelerate his whole body to the speed of the space station. Or to accelerate him up towards the center of the space station.

    That is why I know he will not just start moving with the station.

    My point though is that what holds you to the space station, is a diode effect created, by your body moving. Your body is turned into a diode that allows it to move in a straight line with the velocity applied to it.

    When the floor of the space station gets in the way. The diode created by your body, cannot just stop working or change direction. It continues to work. And as it works, it causes your body to put pressure upon the floor. And create a constant collision with the floor. The floor that does not yield now exerts and creates a new diode effect that moves you body on two axis at once.

    If you study this fully and realize that the constant energy against the floor, is a form of perpetual motion energy that can be measured. You might have to decide to come over to the real world or stay in the pseudo science department.

    Because once spun in space, the space station will continue to spin indefinitely. And continue to create force against the floor.

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    William McCormick
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