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Homework Help: Bicycle vs. pulley, part 2

  1. Jan 5, 2007 #1
    1. The problem statement, all variables and given/known data
    About a year ago I prepared a test for a bicycle on an inclined plane by:
    tying down the handlebars, so they wouldn't move much
    removing the chain
    and tying a wire to a tension scale and the bicycle in 2 ways.
    1. I attached a wire to the rear wheel and the scale, and attached another wire from the scale to a rack at the rear of the bike.
    2. I attached one end of a wire to the point on the front wheel where it touches the ground and the other end to a chain, wrapped the chain around a sprocket on the bottom bracket, attached the other end of the chain to the tension scale, and attached a wire from the tension scale to the front forks.
    see attachment
    If the measurement for 1 is 3 kg, what will be the measurement for 2?

    2. Relevant equations

    3. The attempt at a solution
    From bicycle vs. pulley, part 1 https://www.physicsforums.com/showthread.php?t=148577
    measurement 1 of about 3 kg can be calculated.

    from what I learned from bicycle vs. pulley, part 2https://www.physicsforums.com/showthread.php?t=148808
    I can make the following calculation:
    A ground force of 3 kg is opposed by 3 kg of tension along the wire from the front wheel to the sprocket. 3 kg of torque on the sprocket creates 3 kg of tension along the wire from the sprocket to the front fenders. In other words, both measurements should be the same - about 3 kg.
    However, measurement 1 was about 3 kg, but measurements for 2 were from 2 kg to 2.7 kg.
    So, why weren't they the same? Is there any explanantion besides a faulty test?

    Attached Files:

  2. jcsd
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