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Since centrifugal is not a real force there should be a way to describe it without the centrifugal force.

particularly I want no about how the cycle is not rotating around the axis that is going through the touching points of the two wheels and the ground. My teacher always take the centrifugal force and show us that the torque cancels out with the torque of the weight. But I want to describe it through an inertial observer. According to an inertial observer there is just the torque of weight. But why isn't it rotating.

Qmechanic
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Binuka Perera
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1 Answers1

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If you work from the point of view of the cyclist then, as you say, you need centrifugal force to counteract the torque of the cyclist's weight because you are pretending that the cyclist is in equilibrium.

However, if you work from the point of view of an external observer in an inertial frame of reference, you realise that the cyclist is not in equilibrium because they are not travelling in a straight line. Therefore there is no need to introduce centrifugal force to balance the torque of the cyclist's weight. The cyclist's weight is not balanced, and it is precisely this unbalanced torque that makes the cyclist move along a curve instead of in a straight line.

gandalf61
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  • Can you give me a bit more detailed answer. How does the torque of the weight cause the bicycle to move along a curve? – Binuka Perera Jul 20 '22 at 10:26
  • @BinukaPerera See https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics#Turning for a detailed analysis of the dynamics of a turning bicycle. – gandalf61 Jul 20 '22 at 10:48
  • @BinukaPerera, It's not possible for any object to move around a circular path unless some real force continuously acts on the object, pushing or pulling it toward the center of the circle. We call that real force "centripetal." If the object is a planet orbiting a star, then the centripetal force is gravity. If it's a ball that you're whirling over your head on a string, then the centripetal force is tension in the string. Etc. In the case of a cyclist riding around a circular track, the centripetal force is static friction between the tires and the track. – Solomon Slow Jul 20 '22 at 15:29