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Dec
15
comment What causes the back of a bike to lift when the front brake is applied?
Resolve the two balance equations (for force and torque) for the front and rear wheel upward forces. I have just added a few comments to the page to that effect.
Dec
15
revised What causes the back of a bike to lift when the front brake is applied?
add note about wood block experiment
Dec
15
comment What causes the back of a bike to lift when the front brake is applied?
As the bike does not accelerate vertically, on a level road the sum of the upward forces from the road to the front and rear wheels is equal to the gravitational force with which the earth pulls downwards on the center of mass.
Dec
15
comment What causes the back of a bike to lift when the front brake is applied?
@jcfollower The friction coefficient is not related to the positions of the center of mass or of the hub. Friction coefficient just needs to be large enough for the back to rise. What type of wheel and road and thus friction you need for a given center of mass position to lift off at the back is a separate problem.
Dec
15
awarded  Editor
Dec
15
comment What causes the back of a bike to lift when the front brake is applied?
At -0.54g, the vector sum of the forces on the front wheel contact point points towards the front of the center of mass. This results in clockwise torque, pushing down the rear wheel. At -0.55g, said vector sum points towards the rear of the center of mass, so the resulting torque is lifting the rear wheel.
Dec
15
revised What causes the back of a bike to lift when the front brake is applied?
it is called torque, not angular momentum
Dec
14
awarded  Teacher
Dec
13
comment What causes the back of a bike to lift when the front brake is applied?
Of course, the front wheel friction needs to be large enough to actually deliver the required horizontal decelerating forces.
Dec
13
answered What causes the back of a bike to lift when the front brake is applied?
Dec
13
comment What causes the back of a bike to lift when the front brake is applied?
The front wheel does not need to stop. It only needs to decelerate "quickly enough". That means decelerate the front wheel quicker than the center of mass can be decelerated by a force applied to the contact point between front wheel and road.
Dec
13
comment What causes the back of a bike to lift when the front brake is applied?
The center of mass could be lower than the front axle and the bike would still pivot around the contact point between front wheel and road.