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Flywheel inside a spaceship experiment

  1. Nov 2, 2013 #1

    Given the above setup in this image, there is a fast spinning massive flywheel inside a spaceship. The flywheel is only connected via a lock to a spring.

    What would happen if the retractable steel wall moves towards the steel ball (purple) which is connected to the fly wheel, so the steel ball hits the retractable steel wall of the spaceship .

    The spaceship before the collision is at rest relative to the sun far away.

    Assuming the ball does not destroy the wall, will the spaceship remain at rest to the sun?

    Will the flywheel stop spinning? Will the spring be retracted? (Assume there is a lock to keep the spring in a retracted position once it reaches it's point of max retraction)
  2. jcsd
  3. Nov 2, 2013 #2


    Staff: Mentor

    Your description is a little short of details, IMO. You talk about "a flywheel" but there are two circles in the drawing. Is the flywheel in the shape of a long cylinder that is drawn in perspective? Or are the two outer black lines that connect the circles a belt? How is the red line with the purple ball connected to the flywheel(s)?

    Is there any significance to the small purple balls on the floor?

    Your drawing raises more questions than it answers, IMO.
  4. Nov 2, 2013 #3
    Those are for a follow up question. I think to know the answer to the former, but first i need to make sure i got it right, before asking the follow up. For this question the purple balls can be ignored.

    Yes, it's supposed to look like a long cylinder drawn in perspective. The black lines are the outer layer of the flywheel cylinder. Maybe it was a bad idea to draw it this way in retrospect. A simple 2d perspective would have sufficed i guess.

    The red line is supposed to be connected at about the middle of the fly wheel, down to the spinning axis.
    Last edited: Nov 2, 2013
  5. Nov 2, 2013 #4
    The simplified drawing would look something like this

  6. Nov 2, 2013 #5


    Staff: Mentor

    If the flywheel is a cylinder, how does the red line penetrate through the cylinder? In other words, how is the purple ball connected to the flywheel? Does the flywheel rotate around a fixed axle or does it have a spindle that's mounted in bearings?

    BTW, you seldom see flywheels with this shape (sort of like a rolling pin) where the radius is small in comparison to the width. There's more rotational inertia when the radius is larger.

    What's the purpose of this experiment? Is the idea that if the wall comes in, it pushes the whole flywheel setup? You must have something in mind.
  7. Nov 2, 2013 #6
    The axle is the grey line in the top picture. Imagine a hole somewhere in the middle of the axle that goes from the outer layer of the cylinder down to the axle. Into this hole you stick a rod (the red line). On top of the rod is a metal ball locked to the rod.

    I was thinking of two ways to conduct this. One where the balls is kept on the rod while it hits the wall, and one where you unlock it shortly before it hits it, but i did not want to over complicate it for now.

    Also, you might need a second flywheel that spins the other way around, to make sure the flywheel does not cause the spaceship to spin, seen from the sun. But again, that is not so important for now.

    More important is, if the ship would remain at the same position in space relative to the sun. If the spring would be contracted and how much energy would go into it.
  8. Nov 2, 2013 #7


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    Gold Member

    When I imagine a hole like you describe, from the axle to the outer layer of the cylinder, it means the rod and ball would rotate with the flywheel. That's not going to work.

    It would be easier on those trying to help you if you say what you think is going to happen. That could fill in a lot for what the picture lacks... :rolleyes:
  9. Nov 2, 2013 #8

    Yes, the ball and the rod would rotate with it, and why exactly wouldn't that work?
  10. Nov 2, 2013 #9


    Staff: Mentor

    Regardless of how complicated a device you make, if there is no external force then momentum is conserved and the ship's velocity will not change.
    Last edited: Nov 2, 2013
  11. Nov 2, 2013 #10
    So it will be the ship starting to spin seen from the sun i assume. Setting up the experiment with another flywheel opposing the above and hitting the opposite side of the wall, the springs would retract instead?
  12. Nov 2, 2013 #11


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    Gold Member

    The flywheel needs to be precisely balanced so everything doesn't fly off the axle. Mass would have to be removed from the opposite side of the cylinder. You're process of providing information makes this more like a riddle than sincerely looking for help. You need to explain the experiment - what you expect - or members will grow tired with your current approach.

    Eager to help, but not here to play 20 questions.
  13. Nov 2, 2013 #12


    Staff: Mentor

    Angular momentum is also conserved.

    Your original scenario is already too complicated to follow, and now you want to add more complication? Why? The details are irrelevant, just apply basic conservation laws.
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