Physics Chapter 8
Earth is not spherical but bulges at the equator. Jupiter bulges more. What is the cause of these bulges?
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You hold a meterstick at one end with the same mass suspended at the opposite end. Rank the torque needed to keep the stick steady, from largest to smallest
BCA
When a bowling ball leaves your hand, it may not spin. But farther along the alley, it does spin. What produces the spinning?
Friction between the ball and the lane.
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?
It has a horizontal component that provides the centripital force.
When a car drives off a cliff it rotates forward as it falls. For a higher speed off the cliff, discuss whether the car will rotate more or less.
It will rotate with a greater angular velocity when it is travelling slowly. When the front of the car is just over the edge, the car will not rotate as the center of mass is still above ground, thus negates gravity's torque.
If the world's populations moved to the North Pole and the South Pole, would the 24 hour day become longer shorter, or stay the same?
It would be slightly shorter. Rotational speed increases.
Describe the comparative stablities of the three objects shown in terms of word and potentional energy.
The 1st is the least change in PE and the 3rd recuires the most work....
Assuming your feet are not held down, which is more difficult: doing sit-ups with your knees bent or with your legs straight out.
When your legs are straight out, your center of gravity is further away and you have to work harder to sit up. more torque.
A large wheel is coupled to a wheel with half the diameter, as shown in the sketch. How does the rotational speed of the smaller wheel compare with that of the larger wheel? Discuss the comparisions of the tangential speeds at a rims.
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How can the three bricks be stacked so that the top brick has maximum horizontal displacement from the bottom brick? For example, stacking them as suggested by the dashed lines would be unstable and the bricks would topple.
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Most often we say that force cause acceleration. But when Evan took a ride in a rocket sled at Bonneville Salt lats, blood was forced to the back of his brain, nearly blacking him out. Discuss and identify the cause of this force.
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The spool is pulled in three ways, as shown. There is sufficient friction for rotation. In what direction will the spool roll in each case? Discuss and explain.
In all three cases the spool moves to the right. In the first case there is a torque about the point of contact with the table that rotates the spool clockwise, so the spool rolls to the right. In the second case the pull's line of action extends through the point of table contact, yielding no lever arm and therefore no torque; but with a force component to the right; hence the spool slides to the right without rolling. In the third case the torque produces clockwise rotation so the spool rolls to the right.
Explain why a centripetal force does not do work on a circularly moving object.
There is no component of force parallel to the direction of motion which work requires
Use the equation v=rw to explain why the end of a flyswatter moves much faster than your wrist when you swat a fly.
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With respect to Diana's finger, where is the center of mass of the platic bird? Discuss how this balance can be accomplished during its manufacture.
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A racing car on a flat circular track needs friction between the tires and the track to maintain its circular motion. How much more friction is required for twice the speed?
4 times the force.
Which will have the greater acceleration rolling down an incline: a bowling ball or a volleyball? Defend your answer.
A bowling ball, because a solid sphere has less rotational inertia per mass than other shapes. Its mass is near the rotational axis that extends through its center of mass.
Why are lightweights tires perferred in bicycle racing? Discuss and explain
Because of inertia. Heavier wheels are harder to get spinning than lighter wheels.
Three types of roller are placed on slightly inclinded parallel meterstick tracks as shown. From greatest to least, rank the rollers in terms of their ability to remain stable as they roll.
C, A, B
When you pedal a bicycle, maximum torque is produced when the pedal sproket arms are in the horizontal position, and no torque is produced when they are in the vertical position. Explain
In the horizontal position the lever arm equals the length of the sprocket arm, but in the vertical position, the lever arm is zero because the line of action of forces passes right through the axis of rotation
While riding on a carnival Ferris wheel, Sam Nasty horses around and climbs out of his chair and along the spoke so that he is halway to the axis. How does his rotational speed compare with that of his friends who remain in the chair? How does hi tangentital speed compare? Why are your answers different?
Rational speed will be the same because it is powered. Tangenital speed will be 1/2 because the radial distance is half. They're different because tangential speed is not the same as rotational speed.
If all of Earth's inhabitants moved to the equator, how would this affect Earth's rotational ineratia? How would it affect the length of a day?
Rotational inertia would increase. The day would be longer and the spin would slow.
Why is it easier to carry the same amount of water in two buckets, one in each hand, than in a single bucket>
So you are balanced. Your Center of gravity is in the center of the support base so you don't have to lean.
Using the ideas of torque and center of gravity, explain why a ball rolls down a hill.
The Center of gravity of a ball is not above a point of support when the ball is on an incline. The weight acts at some distance from the point of support which is like a fulcrum. The torque is produced and the ball rotates.
Why does a typical small helicopter with a single main rotor have a second small rotor on its tail? Describe the consequence if the small rotor fails in flight.
The helicopter and main rotor would rotate in the opposite directions. The smaller rotor provides a torque to offset the rotational motion that the helicopter would otherwise have.
Discuss how a ramp would help you to distinugish between two identical looking spheres of the same weight, one solid and the other hallow.
The moment of inertia of a hallow sphere is greater than the solid sphere and so it rolls down slowly.
Is the net torque changed when a partner on a seesaw stands or hangs from her end instad of sitting. (Does the weight or the lever arm change?)
The net torque stays the same. The lever arm will stay the same whether a person stands, sits or hangs from the end.
Flamingos are frequently seen standing on one leg with that other leg lifted. Is rotational inertia enhanced with long legs? What can you say about the bird's center of mass with respect to the flot on which it stands?
Their center of mass is higher and their foot is directly below their center of mass. Rotational inertia is enhanced.
As a car speeds up when rounding a curve, does the centripital force on the car also increase? Defend your answer.
Yes. F=mv^2/r
Why must you bend forward when carrying a heavy load on your back?
You change your center of gravity to keep balanced
Consider a ball rolling around in a circular path on the inner surface of a cone. The weight of the ball is shown by the vector W. WIthout friction only one other force acts on the ball. a normal force. A. Draw a vector for the normal force. b. Using the parallelogram rule, show that the rsultant of the two vectors is along the radial direction of the ball's circular path.
look at notes
The sketch shows a coin at the edge of a turntable. The weight of the coin is shown by a vector W. Two other forces act on the coin-the normal force and force of friction that prevents it from sliding off the edge. Draw force vectors for both of these.
look at notes
The sketch shows a conical pendulum. The bob swings in a circular path. The tension T and weight W are shown by vectors. Draw a parallelogram with these vectors, and show that their resultant lies in the plane of the circle. What is the name of this resultant force?
look at notes
