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Is a bicycle or dirtbike an example of f=ma?

  1. Feb 15, 2009 #1
    Hey all - this is my first post so I mght as well say hi -

    I'm not very smart, but find everyday physics interesting. I tried to look up Newton's Laws, but I can't figure out:

    Is a dirt bike or bicycle a good example of the f=ma principle?

    All the info I found states that the force is a 'pushing' force, i.e, someone pushing the object. I can see the bicycle with the pedals fitting the explanation, but is a dirtbike an example of this law?

    Also, is there a name for the point where the wheel pushes off the ground (propulsion? inertia?) Thanks.
  2. jcsd
  3. Feb 15, 2009 #2
    The interaction between the wheel and the ground is called torque. Torque is the rotational analogue of force. A dirt bike is a good example of F = m A, because the engine produces a force (in the pistons) which produces a torque (through the cams) which rotates the chain which produces a torque on a wheel which rotates the wheeel which produces and acceleration of the bike as a whole.
  4. Feb 15, 2009 #3
    ok - I thought so! Thanks for your help.
  5. Feb 15, 2009 #4


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    Homework Helper

    The name for the "point" is "contact patch", where the tire is in contact with the ground. The torque on the wheel, divided by the radius of the tire equals the backwards horizontal force applied to the ground. The ground "reacts" with an equal and opposite forwards force and this force / mass of (rider + vehicle) = acceleration.
  6. Feb 16, 2009 #5
    When I first read that I was like ":eek:!!", but once I read it again it made sense. Thanks. :approve:
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