Understanding Gyroscopic Effect: Changes in Angular Momentum in Rotating Objects

[firecool]

when a rotating wheel precesses about an axis as in a motorcycle taking a turn it experiences a force in the upward direcion. I've read in my book that this gyroscopic effect takes place due to the principle of conservation of angular momentum.it says the angular momentum changes due to the rotation of the spin axis. but how does the angular momentum change when the mass and the distance from the axis remain the same?how does the angular momentum change by just rotating the spin axis of the wheel and how do we determine the direction in which the force will act? whether upwards or downwards? i know the force acts upwards in the motorcycle because the rider usually bends the m'cycle to counteract this force due to gyroscopic effect and the centrifugal force, but how can we determine the direction of the force in case of an propeller airplane when it takes a right or left turn. the force in this case can be upward or downward.

 

[tiny-tim]

welcome to pf!

hi firecool! welcome to pf!

… how does the angular momentum change when the mass and the distance from the axis remain the same?how does the angular momentum change by just rotating the spin axis of the wheel and how do we determine the direction in which the force will act? …

it's not a force, it's a torque …

when you're riding north and you turn right, you have to change the angular momentum from east to just-south-of-east

since angular momentum is a vector, it obeys the law of vector addition (and subtraction ), so you need to add some angular momentum (roughly) south

ie, you need to tilt the bike to your left or right

you do that by turning the wheel slightly left first … that makes the bike lean a little left, then you do a big turn right to stop the bike falling over

anyway, leaning means that the centre of mass is no longer over the wheelbase, so gravity provides a torque