1Q30.40 - Fluctuating Magnetic Fields/Cons. of Angular Momentum
See also 1Q30.40 in Astronomy.
This demonstration requires a room with a compressed air line.
In most stars the inner core is rotating faster or slower than the outer layer so that there is a readily detectable shear force. If a star has a variable magnetic field and this field increases some of the outer layer are tied to the inner core by the magnetic field and forced to rotate at the same speed. Since total angular momentum is conserved there is a detectable change in the rate of rotation for both systems.
Our version of this is to drop a heavy small diameter rotating mass onto a lighter larger diameter rotating mass. The small diameter plate with the lead strips is approximately 3 times heavier than the rotating air table (small diameter plate contains about 75% of the mass of the total system of the two plates). By gently dropping the heavy mass onto the lighter mass you may demonstrate frictional slippage as the two masses achieve a common rotation rate.
NOTE: There are some sharp edges here so it is advisable to wear gloves when trying to establish your initial rotation rates.
- Yau-Jong Twu, "From Rolling Without Slipping to Sweet Spots", TPT, Vol. 58, #3, Mar. 2020, p. 218.
- Robert Drosd and Leonid Minkin, "Measuring the Coefficient of Kinetic Friction by Exploring Dynamics of Rotational Motion", TPT, Vol. 58, #3, Mar. 2020, p. 176.
- Paul Gluck, "MBL Experiment in Angular Momentum", TPT, Vol. 40, #4, Apr. 2002, p. 230.
- Robert Ehrlich, "F.14. Transfer of Angular Momentum", Turning the World Inside Out and 174 Other Simple Physics Demonstrations, p. 81 - 82.
- Robert Ehrlich, "F.3. Dropping Objects onto a Rotating Casserole Cover", Turning the World Inside Out and 174 Other Simple Physics Demonstrations, p. 69 - 70.
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