Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Gyroscopic question

  1. Jun 19, 2017 #1
    I'm playing with my new Figgit Spinner and it is addictive.

    Of course when I get a good spin going it has a great deal or gyroscopic stability. When I turn my hand in one direction or the other while it is spinning there is the obvious gyroscopic resistance 90 degrees off of the direction of my hand's force.

    My question is this. Obviously there is a force applied to my hand from the spinning gyroscope. The energy for that force must come from the spinner I think? Each time I twist my hand inducing the resistive force from the spinner is that slowing the spinning down a little? In other words, is the force used to resist my hand's turning coming from and subtracting from the spinning energy of the spinner? If not, where does the energy come from?

    thanks,
    tex
     
  2. jcsd
  3. Jun 19, 2017 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    There is no energy transfer unless you rotate it against the torque - and you cannot do that, because the torque is not aligned with your rotation.

    It is a bit similar to the deflection of charged particles in a magnetic field. There is a force, but it is always orthogonal to the direction of motion - the speed (and therefore the energy) does not change.
     
  4. Jun 19, 2017 #3
    When I'm holding the spinning spinner and I tilt my hand so as to move the plane of the rotating spinner I clearly feel a force against my hand resisting the tilting motion.

    Where is that force coming from?

    Tex
     
  5. Jun 19, 2017 #4

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    What you are feeling is actually a Torque. But it is hard to distinguish between the two in a real situation. If you did the experiment on a 'floating platform' you wouldn't actually move up, down or sideways so there isn't actually a Force.
     
  6. Jun 19, 2017 #5

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    From the change of the angular momentum.

    Force and power are different things, and you don't need power to have a force. If you put something on a table, it constantly exerts a force on the table. It doesn't need power to do so.
     
  7. Jun 19, 2017 #6
    Whatever it is, are you saying I'm not feeling a force that my hand works against when I tilt the spinner? I feel it. It works against my hand. That is a force....isn't it?

    And if so...does it come from the spinning disk?

    And if so...doesn't the expenditure of that energy slow down the spinning?

    Tex
     
  8. Jun 19, 2017 #7

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    You feel it, but you do not work (with the meaning of energy) against it. You rotate the device in a different direction.
    It is like the book on the table I mentioned earlier. Hold it in your hand and move it around horizontally. You feel its force downwards, but you do not change its potential energy, because you do not change its height. No work is done.

    Your muscles will actually expend some energy to hold the book, but that is an internal biological process, it is not work done at the book.
     
  9. Jun 20, 2017 #8

    A.T.

    User Avatar
    Science Advisor
    Gold Member

    What you feel are deformations, which are related to forces (or pressures exerted by those forces). Those forces (and your sensation) do not depend on the choice of reference point, like the torques. So it makes no sense to me to say, that you "feel" torques.

    There are forces, if you feel something. You might mean that there is no net force.
     
  10. Jun 20, 2017 #9

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    What do you feel when you grab a rotating shaft? Your body sensors work on forces, I agree but what has that got to do with the way your brain makes sense of the torque it feels?
     
  11. Jun 20, 2017 #10

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    What I was getting at is that there is a popular idea that gyroscopes can provide a net force. The forces from a gyroscope cannot provide a 'reactionless driving force'. The force you 'feel' is actually one of a pair of forces which constitute a torque. The effect of trying to turn the spinner is a torque that acts to turn your hand at right angles to the axis that you are pressing against. The energy for disturbing the spinner comes from your hand and not the spinning disc. If the bearing is good then the friction is low enough not to take appreciable energy as the load on the bearing changes.
    Look at this link. It can enlighten you or confuse you more. It's good fun though.
     
  12. Jun 20, 2017 #11
    My hand is working harder than it would otherwise, isn't it, to counter the force "that acts to turn your hand"? Is there not a equal and opposite force involved here. If I am working harder than normal to tilt the spinning disk as opposed to a non-spinning disk is it not because I am working against an opposing force? Im not trying to argue but I don't understand. Isnt this the very principle used in ship stabilizers to keep a ship stable? The massive gyros exert a force (or torque or whatever the term) which resist any tilting of the ship. If the ship tilts SOMETHING (I don't apparently understand what) about the gyro resists it. Isn't that a force of some kind from the gyro?

    tex
     
  13. Jun 20, 2017 #12

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Not with the physical meaning of working.

    Your hand muscles need more energy.

    See the example of holding a book. Muscles need energy to hold it, but no energy is transferred to the book. The hand just warms up a bit as the muscles act against themselves.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Gyroscopic question
  1. Gyroscope question (Replies: 19)

Loading...