[Physics] In which direction does mud fly off a moving bike’s tire & why

angular velocityclassical-mechanicsforcesrotational-dynamics

If a bike moves through a muddy area, mud gets on its tires. Then the mud flies off from the tires.

Which forces are acting on it? In which direction does it fly off?

On my physics test, I wrote that it flies off along tangential velocity at that point, but it was marked incorrect.

Best Answer

You were probably expected to note that the path of any point of the tire is a cycloid. At the point of contact with the ground, the tire is not moving. As it rises from the ground it is moving faster, with a speed that is $v(1+\sin \theta)$ where $v$ is the bike speed and $\theta$ is measured counterclockwise from horizontal. The centrifugal force is rising as $\theta$ decreases from $270^\circ$ and at some point it exceeds the strength of the attachment to the wheel. When it lets go it should get the tangential velocity of that point of the wheel, which is not the same as the speed of the bike.

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