Bicycle Gyroscope

INTRODUCTION

In physics, angular momentum is a vector quantity which represents the product of a body's rotation of velocity and rotation of inertia in a particular axis. The angular momentum of turning bicycle wheels makes them act like gyroscopes to help stabilize the bicycle. This gyroscopic action also helps to turn the bicycle. A bicycle held straight up will tend to go straight. If the rider leans left, a torque will be produced which causes a counterclockwise precession of the bicycle wheel, tending to turn the bicycle to the left. The wheel has an angular momentum that is large because its mass is centered at the rim of the wheel, causing the wheel to stand up on its own.

MATERIALS

*Bicycle wheel (with removable rope)

*Low friction rotating stool

*Chair

PROCEDURE

Get the bicycle wheel and spin it with your hand and hold it with the rope. The rope makes the wheel presses. You’ll notice that the wheel is able to balance on the rope; it resists motion about the spin axis in very odd ways. This is defies gravity.

Stand on top of the rotating stool. Get the bicycle wheel and spin the bicycle wheel. This will demonstrate Newton's third law (action and reaction) and the conservation of angular momentum. Make the stool rotate to the left and right by turning the axis of the bicycle wheel in different directions.

Next, place the chair on top of the rotating stool and sit on it. Do the same thing you did when you were standing on the stool.

SCIENTIFIC PRINCIPLE

A rotating bicycle wheel has angular momentum, which is a property involving the speed of rotation, the mass of the wheel, and how the mass is distributed.

The wheel has an angular momentum that is large because its mass is centered at the rim of the wheel, causing the wheel to stand up on its own.

The gyroscope provides an example of the conservation of angular momentum. The angular momentum is a vector quantity which represents the product of a body's rotation of velocity and rotation of inertia in a particular axis. The direction and magnitude of this vector will remain constant. Friction produces a torque that decreases the magnitude of the vector and eventually causes the gyroscope to stop spinning.

If you want to change the angular momentum of a bicycle wheel, you can change the direction. To change the direction, you must exert a twisting force, called a torque, on the wheel. The bicycle wheel will exert an equal and opposite torque on you. When you twist the bicycle wheel, the bicycle wheel will twist you the opposite way. If you are sitting on a rotating stool, the wheel will make you turn. This is how angular momentum affects an object's motion.

Gravity produces a torque perpendicular to both the axis of the gyroscope and the vertical, and causes the horizontal precession. Precession is the downward pull of gravity that tries to make the wheel rotate faster at the bottom than at the top. Since the wheel is rigid, this can happen only if the wheel moves horizontally in the direction in which the bottom of the wheel is spinning.

When force is applied to the axle of a bicycle wheel, the section at the top of the gyroscope will try to move to the left, and the section at the bottom of the gyroscope will try to move to the right. If the gyroscope is not spinning, then the wheel flops over.

If the gyroscope is spinning, think about what happens to these two sections of the gyroscope: Newton's first law of motion states that a body in motion continues to move at a constant speed along a straight line unless acted upon by an unbalanced force. So the top point on the gyroscope is acted on by the force applied to the axle and begins to move toward the left. It continues trying to move leftward because of Newton's first law of motion, but the gyro's spinning rotates it.

SAFETY REGULATIONS

Be careful when making the wheel stop spinning. You can easily get dizzy on the rotating stool; it can make you fall when getting off the stool. Pause to regain equilibrium before stepping off the stool. Be careful not to catch your fingers in the rotating wheel.