Rotational Motion (Torque & Centrip.)
Terminology – give the definition of each in your own words. Include the symbol and units for each.
Tangential speed (symbol )–
Units –
Rotational (angular) speed (symbol Units –
)–
Angular acceleration (symbol Units –
(Linear) Inertia (symbol Units –
)–
)–
Rotational Inertia (symbol Units –
)–
Write the expression for rotational inertia for a very small object of mass M swinging in a circle of radius R about an axis.
Torque (symbol Units –
)–
Angular Momentum (symbol Units –
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Center of mass ( do not use the word “gravity”.) –
Centripetal Acceleration (symbol Units –
)–
Stability –
1. Review question – For an object to accelerate linearly, what is needed?
2. For an object to change its rotational speed (rotational or angular acceleration), what is needed?
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Rotational Motion (Torque & Centrip.)
3. From a point of view of physics, explain what you do and why when you run as fast as possible.
4. How is “torque” calculated (two ways)?
5. Why is it important to be able to find a “center of mass” of an object?
6. How is “angular momentum” calculated (two ways)?
You don’t have to memorize rotational motions as if they are totally new. If you are firm about linear motions (terminology,
and their relations), then all you have to do is to convert them to rotational motion with new notations. Then, the only thing
you have to learn is “new letters”. You might consider making a table of these factors.
7. Describe and explain (give the physics) what you see if you start a hoop, a solid disk, a hollow ball, and a solid ball
down an incline at the same time.
8. Say you are driving a car, turning in a counter-clockwise circular motion. Explain “centripetal force” and your
perception of the unreal “centrifugal force” using every thing you learned up to now.
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Rotational Motion (Torque & Centrip.)
9. Review question – when can you apply “conservation of linear momentum”?
10. When can you apply “conservation of angular momentum”?
11. Suppose you have a merry-go-round with mass of 100kg and a radius of 1m. Further, suppose you are applying a
force of 50N at, and tangential to the rim of the merry-go-round. What torque are you applying?
12. Calculate the rotational inertia of the merry-go-round. ( note: rotational inertia = 1/2MR2 )
13. Now find the angular acceleration of the merry-go-round.
14. If you applied this torque for 30 seconds, what would be the angular speed of the merry-go-round?
15. Ok, now give a shot at finding the angular momentum, the rotational kinetic energy and the work done.
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