Tita Test 12

Momentum is conserved when there is no net external force. When is angular momentum conserved?

when there is no torque acting on it

What happens to the rotational inertia of an object if its mass is extended farther away from the axis of rotation?

The rotational inertia increases

Which will swing to and fro more often, a short pendulum or a long pendulum?

The short one will swing quicker in a to-and-fro motion due to less rotational inertia

which has more rotational inertia a solid sphere of mass or cylinder

cylinder

Does the angular momentum of a rotating system change when no unbalanced external torques act on it?

no it does not change it is constant

Which will have the greater acceleration rolling down an incline -- a hoop or a solid disk?

the solid disk

Why is a stick with a wad of clay at the top easier to balance in the palm of your hand then an empty stick?

the wad of clay at the top has more rotational inertia

The text says that angular momentum is Iω, then says it is mvr. Which is i

they are both the same

Perky rides at different radial distances from the center of a turntable that rotates at a fixed rate. His distances and tangential speeds at three different locations are as follows. (A) r = 15 cm, v = 7.5 cm/s (B) r = 10 cm, v = 5.0 cm/s (C) r = 5.0 cm, v = 2.5 cm/s

A,B,C

What happens to a rotating object that is not acted on by an external torque?

According to Newton's first law of inertia for rotating systems, the object's rotational the motion does not change

How and why do you throw a football so that it spins about its long axis when traveling through the air

Angular momentum about the long axis maintains stability.

Beginning from a rest position, a solid disk A, a solid ball B, and a hoop C, race down an incline. Rank them in order of finishing: winner, second place, and third place

B,A,C

Why does bending your legs when running enable you to swing your legs to and fro more rapidly?

Bent legs have less rotational inertia than long straight legs.

Two solid disks with the same shape but different sizes are rolled down an incline. Which disk reaches the bottom first? Explain.

Both disks reach the bottom at the same time because of all objects of the same shape but different size have the same "laziness per mass," meaning that they accelerate equally

Circle the letter of the sequence that correctly ranks, from lowest to highest, the rotational inertia of the following: (A) a baseball bat held at its narrow end; (B) a baseball bat held at its more massive end; (C) a meter stick held at its midpoint.

C,B,A

Three iron shapes of the same mass rotate about the axis shown by the circle with the dot inside. Rank them, from greatest to least, in terms of the rotational inertia about this axis.

C,B,A

Students Art, Bart, Cis, and Dot sit on a rotating turntable at different distances from the center as indicated. (A) Art, m = 60 kg, sits at r. (B) Bart, m =25 kg, sits at r. (C) Cis, m = 50 kg, sits at r. (D) Dot, m = 20 kg, sits at r. From greatest to least, rank the angular momenta of the four students.

C,D,B,A

Is the following sentence true or false? Newton's first law does not apply to rotating objects.

False

How can gravity be simulated in an orbiting space station?

Gravity is simulated by a fictitious, centrifugal force if the space station spins

If you walked along the top of a fence, why would holding your arms out help you to balance?

It increases your rotational inertia and helps you to balance by making your body more resistant to toppling.

If you walked along the top of a fence, why would holding your arms out help you to balance?

It increases your rotational inertia and helps you to balance by making your body more resistant to toppling.

Gather a selection of canned foods. Predict which will roll faster down an incline. Compare liquids (which slide or slosh rather than roll inside the can) and solids. Roll the cans to test your predictions. Describe your results.

Liquids roll faster because the PE becomes mainly translational KE with little rotational KE.

What is the law of inertia for rotation?

Rotating objects tend to remain rotating

Circle the letter of each statement that is true of rotational inertia. a. Rotational inertia depends on the force of gravity. b. Rotational inertia depends on the mass of an object. c. Rotational inertia depends on the distribution of mass in the object. d. Rotational inertia is always constant

Rotational inertia depends on the mass of an object. Rotational inertia depends on the distribution of mass in the object.

Stand two metersticks against the wall and let them topple over. Now put a wad of clay on top of one of the sticks and let them topple again. Which reaches the floor first?

The bare stick has less rotational inertia and hits the ground first.

Explain how angular momentum makes a moving bicycle easier to balance than a bicycle at rest.

The bicycle wheels at rest have no angular momentum, and the bicycle will fall over easily. When the bicycle is moving, the wheels have angular momentum, and a greater torque is required to change the direction of the angular momentum

Explain why a tightrope walker might hold a long pole in the horizontal position while performing.

The pole increases the performer's rotational inertia, allowing him or her to resist rotation.

A sizable quantity of soil is washed down the Mississippi River and deposited in the Gulf of Mexico each year. What effect does this tend to have on the length of a day?

The soil moves farther away from Earth's axis. By conservation of angular momentum, like a skater extending their arms, Earth's rotation slows, making the days slightly longer.

Angular momentum is a quantity.

True

Is the following sentence true or false? A cat dropped upside down will twist and land on its feet while maintaining a state of zero angular momentum

True

Is the following sentence true or false? According to the law of inertia, rotating objects tend to keep rotating

True

Is the following sentence true or false? Any moving object has momentum

True

Is the following sentence true or false? As the distance between an object's mass concentration and its axis of rotation increases, its rotational inertia increases.

True

Is the following sentence true or false? The three major axes of rotation of the human body are at right angles to one another and pass through the center of gravity

True

Is the following sentence true or false? When the rotational speed is assigned a direction, it is known as rotational velocity

True

Which will have the greater acceleration rolling down an incline -- a bowling ball or a volleyball? Defend your answer.

a bowling ball (solid) -- it has less rotational inertia per mass

Circle the letter of each true statement. a. Rotational velocity is a vector quantity. b. Rotational velocity has the same direction as angular momentum. c. Rotational velocity lies along the axis of rotation of an object. d. An object's rotational velocity is equal in magnitude to its angular momentum

a. Rotational velocity is a vector quantity. b. Rotational velocity has the same direction as angular momentum. c. Rotational velocity lies along the axis of rotation of an object.

Circle the letter of each statement that is true. a. The human body's longitudinal axis runs from head to toe. b. The human body's longitudinal axis passes through the center of gravity. c. Much of the body's mass is concentrated along the longitudinal axis. d. The human body's longitudinal axis has the least rotational inertia of the three body axes.

all of the above

In equation form, angular momentum is written as

angular momentum = rotational inertia (I) rotational velocity

define angular momentum? discuss how conservation of angular momentum is applied to a gymnast starting from a standing position and turning a somersult in the air

angular momentum is the product of rotational inertia and rotational velocity. The gymnast would have to use the transverse axis to turn

Circle the letter of the equation that is used to determine the rotational inertia, I, of a solid sphere spinning about its axis of rotation. a. I = (1/12)mL2 b. I = mr2 c. I = (2/5)mr2 d. I = (1/3)mL2

c. I = (2/5)mr2

You sit in the middle of a large, freely rotating turntable at an amusement park. If you crawled toward the outer rim, would the rotational speed increase, decrease, or remain unchanged

decreases in accordance with the conservation of angular momentum.

Is the following sentence true or false? An object with a great rotational inertia will roll down an incline more quickly than one with a small rotational inertia.

false

Is the following sentence true or false? Any hollow cylinder will roll down an incline with more acceleration than any solid cylinder.

false

Is the following sentence true or false? The angular momentum of a small object rotating at a very large radial distance is equal to its linear momentum

false

Is the following sentence true or false? The rotational inertia of an object is constant and cannot change.

false

Is the following sentence true or false? When doing a cartwheel, a person rotates about his or her transverse axis.

false

When a gymnast goes from an outstretched position into a tuck, her rate of rotation______

increases

What does it mean to say that angular momentum is conserved?

it does not change after some event

If a skater who is spinning pulls her arms in so as to reduce her rotational inertia to half, by how much will her rate of spin increase?

it doubles

How can a skater decrease his or her rotational inertia while spinning?

it will remain the same by the conversion of rotational momentum

How does a skater decrease his or her rotational inertia while spinning?

By pulling their arms inward and "balling up"

Inertia can be thought of as a measure of

laziness

If the world's populations move to the North and South Poles, would the length of a day increase, decrease, or stay the same?

less mass at the equator and increases the speed of the earths rotation making the days slightly shorter

The major axes of rotation of the human body are the ____________ axis, the_______, and the_______ axis.

longitudinal transverse medial

If all of Earth's inhabitants moved to the equator, how would this affect Earth's rotational inertia? How would it affect the length of a day?

more mass at the equator that means mass is concentrated further away from earth axis and therefore the rotational inertia increases. Earths angular momentum would slow it down

If a skater who is spinning pulls her arms in so as to reduce her rotational inertia to half, by how much will her angular momentum increase?

none the angular momentum is conserved

A _____________pendulum swings back and forth more rapidly than a ___________pendulum because the__________ pendulum's rotational inertia is smaller

short long short

At the circus, a performer balances his friends at the top of a vertical pole. Why is this feat easier for the performer than balancing an empty pole?

the pole with people at the top has more rotational inertia

A ____________is required to change the rotational state of motion of an object.

torque

Circle the letter of the phrase that describes the "up" direction sensed by a person in a large rotating space.

toward the center of rotation

During a somersault, a person rotates about her_______ axis.

transverse

Is the following sentence true or false? It is easier to spin when your body is in a tucked position than when it is outstretched.

true

Is the following sentence true or false? Objects in a rotating reference frame seem to experience an outwardly directed centrifugal force.

true

Is the following sentence true or false? The angular momentum of a rotating system is conserved if no external torque acts on it.

true