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Q & A: Precession of a spinning wheel

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Most recent answer: 05/16/2013
Why when holding a spinning wheel at one end of its axis, does the wheel spin in a circle and stay parallel to the ground?
- kevin (age 17)
New Jersey
Hi Kevin,  
What you are describing is a form of gyroscope.   The turning of the system in a circle is called precession. It is due to the fact that the downward force of gravity acting on the center of mass of the wheel and the upward force of your hand holding the end of the shaft produce a turning torque on the system.  The spinning wheel has angular momentum, a quantity akin to linear momentum.  Just as a force produces a change in linear momentum, a torque produces a change in angular momentum which results in precession.  The math is a bit complicated but you can look at:
   for some explanations.


(published on 05/16/2013)

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