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Date: Rotational Motion Study Guide
Please write the definition, variable, and units for the following terms: Angular displacement
Angular velocity (rotational speed)
Angular acceleration
Tangential speed (velocity)
Rotational inertia
Torque
Angular momentum
Center of mass (center of gravity)
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Centripetal force
Centrifugal force
Angular momentum
Be able to explain the answers to the following questions about rotational motion using key terms. Why does a spinning person speed up when they pull their arms in?
Draw a picture of the meterstick set-up from the torque lab. What are some ways you could balance the torques on the meterstick?
What causes centripetal force in the following situations: The earth going around the sun
A person swinging a rubber stopper around with a rope
A car turning on a road a person riding the gravitron
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If you add more hanging mass to the weight in the centripetal force lab, what do you have to do to the stopper to keep the forces balanced?
If you add more hanging mass to the weight in the centripetal force lab, what do you have to do to the radius to keep the forces balanced?
Where is the center of mass in a baseball? In a baseball bat?
What are the conditions of mechanical equilibrium?
Where should you stand on a merry-go-round to experience the greatest linear speed?
Can a force produce a torque when there’s no lever arm?
Can an object move along a curved path if no force acts on it?
When you are in a car turning to the left, you may find yourself pressed against the right-side door. Why do you press against the door? Why does the door press on you? Does your explanation involve centrifugal force or Newton’s Laws?
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Explain why a centripetal force does not do work on a circularly moving object.
Where should you stand on a merry-go-round to experience the greatest rotational speed?
What can you do to make it easier to lift a rock using a lever?
What can you do to make it easier to lift a rock using a pulley?
Why would a tightrope walker carry a pole?
Which will have a greater acceleration rolling down an incline --- a bowling ball or a volleyball? Defend your answer.
If all Earth’s inhabitants moved to the equator, how would this affect Earth’s rotational inertia? How would it affect the length of the day?
Friction is needed for a car rounding a curve. But, if the road is banked, friction may not be required at all. What, then, supplies the needed centripetal force?
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Review and be able to answer any questions about labs. Math practice: Write equations for torque:
Write equations for centripetal force:
Write equation for velocity of an object going in a circle (from lab):
1. A force of 20 N is applied perpendicular to the end of a bar of length 0.5 m. Calculate the torque produced by the force.
2. A child of mass 20 kg is located 2.5 m from the fulcrum or pivot point of a seesaw. Where must a child of mass 30 kg sit on the seesaw in order to provide balance?
3. A bike pedal is 45 cm from the axle. How much torque does a 400 N girl standing on the pedal exert when (i) it is horizontal?
(ii) it is at its lowest point?
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4. Determine the torque on a bolt, if you are pulling with a force of 200 N directed perpendicular to a wrench of length 20 cm?
5. Calculate the force required to produce 20 Nm torque at an angle of 50º from along a 300 cm rod?
6. You are sitting 2.5m from the pivot of a teeter totter. Your friend Uriah is sitting on the other side of the teeter totter, 3.0m from the pivot. If your mass is 70. kg and Uriah's mass is 60. kg, where should your 35kg little brother Tongo sit so you will all balance?
7. A rock tied to a string is traveling at a constant speed of 4 m / s in a circle of radius 1.5 m. Calculate the magnitude of the centripetal acceleration of the rock. What is the direction of the acceleration?
8. A 1.3 m long fishing line rated as "10 lb test" that can stand a force of 10 lb (44.48 N) is attached to a rock of mass 0.5 kg. Calculate the maximum speed at which the rock can be rotated without breaking the line.
9. A rock tied to the end of a string moves in a circle at a constant speed of 2.5 m / s and experiences an acceleration of 4.0 m / s2. What is the radius of the circle of its motion?
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10. A rock tied to the end of a string moves in a circle of radius 1.2 m with a constant speed of 3.0 m / s. Calculate the centripetal acceleration of the rock.
11. A satellite of mass 500 kg is placed in an orbit of radius 5 times the radius of the Earth, i.e. the distance between the satellite and the center of the Earth is equal to 5 Earth radii. Calculate the centripetal force experienced by the satellite. The radius of the Earth is 6.37 x 106 m.
12. The distance from the Earth to the Sun is 1.5 x 1011 m (93 million miles), and the time for one complete orbit of the Earth about the Sun is one year. How long would it take for a planet located at twice this distance from the Sun to complete one orbit?
13. A car of mass 1000 kg travels around a level curve of radius 40 m. If the maximum frictional force that can be exerted upon the car by the road (determined by the coefficient of friction between the tires and the road) is 7000 N how fast can the car travel without "spinning out?"
