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| Deletions are marked like this. | Additions are marked like this. |
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| 1. Select a volunteer (possibly yourself), and have him or her carefully step onto the platform. | |
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| 1. Have the volunteer tilt the wheel so that the plane of rotation approaches horizontal. This will set him or her into rotational motion in a direction opposite that of wheel. The volunteer can control his or her speed by the degree of tilt from vertical. 1. To stop the wheel, warn the volunteer that you are about to do so, and tell him or her to hold the wheel firmly. Then, using a hand or two, slowly grip the tire until the wheel comes to a stop. After the wheel stops, you can take the wheel from the |
1. Have the volunteer tilt the wheel so that the plane of rotation approaches horizontal. This will set him or her into rotational motion in a direction opposite that of wheel. The volunteer can control his or her speed by the degree of tilt from vertical. The maximum speed will be reached when the plane is fully horizontal. 1. To stop the wheel, warn the volunteer that you are about to do so, and tell him or her to hold the wheel firmly. Then, using a hand or two, slowly grip the tire until the wheel comes to a stop. After the wheel stops, you can take the wheel from the volunteer, and have him or her carefully step off of the platform. |
| Line 48: | Line 49: |
| First have the volunteer raise the bicycle wheel vertically over there head, with the wheel not spinning and then with it spinning. The volunteer must hold the spinning bicycle wheel by the ends of its axle horizontally at arms length. Have the bicycle wheel spun up to high speed by hand and give it to either the instructor or a volunteer or whomever is standing on the rotating platform. Again have them hold the bicycle wheel firmly by its handles while standing on a rotating platform to help illustrate Newton's third law (action and reaction) and the conservation of angular momentum. One can sit on a stool that is placed on the rotating platform as well. The person now can rotate one direction or the other by turning the axis of the bicycle wheel in different directions. For best results, orientate the spinning bicycle wheel's axis perpendicular to it original direction, so that it is vertical or parallel to the rotational axis of the platform. This well transfer the most angular momentum to the rotating platform to make the platform and person rotate the opposite direction of the spinning bicycle wheel. |
When the wheel is spun, it is given some amount of angular momentum whereas the volunteer has none (starting from rest). When the volunteer tilts the wheel, he or she is applying a torque to it and thereby changing its angular momentum. By the conservation of angular momentum (or equivalently Newton's third law), the volunteer feels a torque from the wheel applied in the opposite direction causing him or here to start spinning in a direction opposite that of the wheel. The applied change in angular momentum will be greatest when the torque is applied through an angle of 90°. This is because torque is related to angular acceleration by τ = I*α where I is the moment of inertia of the wheel. α become negative once we pass the 90° mark thereby causing the volunteer to start slowing down. |
[:PiraScheme#Mechanics: Table of Mechanics Demonstration] |
[:MEEquipmentList: List of Mechanics Equipment & Supplies] |
[:Demonstrations:Lecture Demonstrations] |
Human Gyroscope, 1Q50.15
Topic and Concept:
Rotational Dynamics, [:RotationalDynamics#Gyros: 1Q40. Gyroscopic Motion]
Location:
Cabinet: [:MechanicsCabinet:Mechanic (ME)]
Bay: [:MechanicsCabinetBayB9:(B9)] & [:MechanicsCabinetBayB12:(B12)]
Shelf: #1
attachment:HumanGyro04-400.jpg
Description:
One stands on a rotating platform and with a spinning bicycle wheel, rotate the bicycle wheel so that it transfer some of it's energy to the rotating platform.
Equipment |
Location |
ID Number |
|
|
|
Rotating Platform |
ME, [:MechanicsCabinetBayB9: Bay B9, Shelf #1] |
|
Bicycle Wheel |
ME, [:MechanicsCabinetBayB12: Bay B12, Shelf #1] |
|
Important Setup Notes:
- Demonstration may require practice.
- A volunteer may be required.
Setup and Demonstration:
- Set Rotating Platform out on the floor.
- Level the platform.
- Select a volunteer (possibly yourself), and have him or her carefully step onto the platform.
- Get the wheel spinning by grasping a handle (the axle) with one hand. Then, grabbing the outer rim with the other hand, apply a strong, tangential force.
- Hand off the spinning wheel with its plane of rotation vertically oriented to the volunteer (you should still be holding on to the axle) having him or her hold onto the axle with both hands, one on either side. Tell him or her to keep his or her arms straight so as not to bump and thereby slow down the spinning wheel.
- Have the volunteer tilt the wheel so that the plane of rotation approaches horizontal. This will set him or her into rotational motion in a direction opposite that of wheel. The volunteer can control his or her speed by the degree of tilt from vertical. The maximum speed will be reached when the plane is fully horizontal.
- To stop the wheel, warn the volunteer that you are about to do so, and tell him or her to hold the wheel firmly. Then, using a hand or two, slowly grip the tire until the wheel comes to a stop. After the wheel stops, you can take the wheel from the volunteer, and have him or her carefully step off of the platform.
Cautions, Warnings, or Safety Concerns:
- Fingers, long hair, and necklaces may get caught in the spooks of the moving bicycle wheel. Take precautions!
- Due to the high rotational speed of the bicycle wheel, stopping the wheel can be difficult.
- The volunteer may get dizzy from spinning.
Discussion:
When the wheel is spun, it is given some amount of angular momentum whereas the volunteer has none (starting from rest). When the volunteer tilts the wheel, he or she is applying a torque to it and thereby changing its angular momentum. By the conservation of angular momentum (or equivalently Newton's third law), the volunteer feels a torque from the wheel applied in the opposite direction causing him or here to start spinning in a direction opposite that of the wheel. The applied change in angular momentum will be greatest when the torque is applied through an angle of 90°. This is because torque is related to angular acceleration by τ = I*α where I is the moment of inertia of the wheel. α become negative once we pass the 90° mark thereby causing the volunteer to start slowing down.
attachment:HumanGyro02-250.jpg |
attachment:HumanGyro01-250.jpg |
attachment:HumanGyro03-250.jpg |
attachment:HumanGyro04-250.jpg |
attachment:RotatingPlatform-02-250.jpg |
attachment:RotatingPlatform-03-250.jpg |
attachment:BicycleWheel-01-250.jpg |
Videos:
[https://www.youtube.com/user/LectureDemostrations/videos?view=1 Lecture Demonstration's Youtube Channel]
References:
[http://sprott.physics.wisc.edu/demobook/chapter1.htm Sprott - Demobook: Chapter1]
[http://sprott.physics.wisc.edu/demobook/uwpress.htm Sprott - Physics Demonstrations]
[https://en.wikipedia.org/wiki/Gyroscope Wikipedia - Gyroscope]
[https://en.wikipedia.org/wiki/Angular_momentum Wikipedia - Angular Momentum]
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