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chapter8 Flashcards

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1
Q

What are the units of measurement for tangential speed? For rotational speed?

A

m/s for tangential, RPM for rotational

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2
Q

On a rotating turntable, how do tangential speed and rotational speed vary with distance from the center?

A

Tangential speed increases with distance. Rotational speed is constant.

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3
Q

Rotational inertia about the midpoint of an object becomes greater with _______.

A

increased mass and increased distance to mass concentration

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4
Q

Inertia depends on mass; rotational inertia depends on mass and something else. What?

A

The distribution of mass about the axis of rotation

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5
Q

How does the lever arm change if you decrease the angle of the force?

A

It decreases

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6
Q

How does the lever arm change when you decrease the distance to the nut?

A

it decreases

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7
Q

How does the force needed to turn the wrench change if you increase the lever arm?

A

it decreases

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8
Q

What does a torque tend to do to an object?

A

Torque tends to twist or change the state of rotation of the object.

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9
Q

What is meant by the “lever arm” of a torque?

A

It is the perpendicular distance from the rotational axis to the line along which the force acts.

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10
Q

How do clockwise and counterclockwise torques compare when a system is balanced?

A

They are equal in magnitude and opposite in direction.

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11
Q

The center of gravity of a basketball is located _______.

A

at its geometrical center

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12
Q

If you toss a stick into the air, it appears to wobble all over the place. Specifically, about what place does it wobble?

A

It will rotate about the center of mass.

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13
Q

What is the relationship between the center of gravity and the support base for an object that is in stable equilibrium?

A

A vertical line through the center of gravity must pass inside the support base of the object

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14
Q

Why doesn’t the Leaning Tower of Pisa topple over?

A

A vertical line through the center of gravity passes inside its support base

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15
Q

When a rock tied to a string is whirled in a horizontal circle, doubling the speed _______.

A

quadruples the tension in the string

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16
Q

When you whirl a can at the end of a string in a circular path, what is the direction of the force you exert on the can?

A

Toward the center of the circle

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17
Q

If the string that holds a whirling can in its circular path breaks, what kind of force causes it to move in a straight- line path: centripetal, centrifugal, or no force? What law of physics supports your answer?

A

No force; Newton’s first law

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18
Q

If you are not wearing a seat belt in a car that rounds a curve, and you slide across your seat and slam against a car door, what kind of force is responsible for your slide: centripetal, centrifugal, or no force?

A

There is no force as viewed by someone outside the car. To them you move in a straight line

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19
Q

Why is centrifugal force in a rotating frame called a “fictitious force”?

A

It is not a fundamental force of nature. Instead, it is a force that only appears in an accelerating frame of reference

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20
Q

How can gravity be simulated in an orbiting space station?

A
  • Rotate a cylinder to create centrifugal force as viewed by a person on the inside of the curved outer wall
  • Spin two pods connected by a cable
  • Spin a station shaped like a bicycle wheel
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21
Q

Distinguish between linear momentum and angular momentum

A

Angular momentum depends on the distribution of mass, whereas linear momentum depends on the total mass.

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22
Q

What is the law of inertia for rotating systems in terms of angular momentum?

A

Angular momentum does not change without an applied external torque.

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23
Q

Consider someone in a rotating space habitat. Rotational motion provides

A

a support force

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24
Q

What is required to change the angular momentum of a system?

A

external torque

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25
Q

When the rotational speed of a rotating system doubles, its angular momentum _______.

A

doubles

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26
Q

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

A

Her angular momentum does not change. Her spin rate doubles

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27
Q

Your pet hamster sits on a record player that has constant angular speed. If the hamster moves to a point twice as far from the center, then its linear speed

A

doubles

28
Q

The circumference of a bicycle wheel is 2 meters. If it rotates at 1 revolution per second then its linear speed is

A

2 m/s

29
Q

Consider a string with several rocks tied along its length at equally spaced intervals. You whirl the string overhead so that the rocks follow circular paths. Compared with a rock at the end of the string, a rock at the middle moves

A

half as fast

30
Q

The net force exerted on a car traveling in a circular path at constant speed is

A

directed toward the center of the curve

31
Q

If you’re on a Ferris wheel at a carnival, seated 10 m from the Ferris wheel’s axis that makes a complete rotation each minute, your linear speed is

A

62.8 m/min.

32
Q

The rotational inertia of your leg is greater when your leg is

A

straight

33
Q

A ring and a disk both at rest roll down a hill together. Which rolls slower?

A

ring

34
Q

A ring, a disk, and a solid sphere begin rolling down a hill together. Which reaches the bottom first?

A

sphere

35
Q

A vertically-held sledge hammer is easier to balance when the heavier end is

A

at the top, away from your hand.

36
Q

Which tin can will roll down an incline in the shortest time, one filled with water or one filled with ice? (Hint: water ‘slides’ inside the can.)

A

with water

37
Q

Compared with a force, a torque involves

A
  • distance from an axis of rotation.
  • leverage.
  • rotation.
38
Q

A torque acting on an object tends to produce

A

rotation

39
Q

A ball that gains speed as it rolls down a hill experiences a

A

net force and net torque

40
Q

If you place a pipe over the end of a wrench when trying to rotate a stubborn bolt, effectively making the wrench handle twice as long, you’ll multiply the torque by

A

two

41
Q

For a system in mechanical equilibrium, the resultant

A

force must be zero.

torque must be zero

42
Q

Two people are balanced on a seesaw. If one person leans inward toward the center of the seesaw, that person’s end of the seesaw tends to

A

rise

43
Q

To rotate a stubborn screw, it is best to use a screwdriver that has a

A

wide-handle

44
Q

On a balanced seesaw, a boy three times as heavy as his partner sits

A

1/3 the distance from the fulcrum

45
Q

A solitary boy cannot balance on a seesaw with its fulcrum at its midpoint. If the fulcrum is moved to one-quarter the distance from the boy, balance is achieved when the weight of the boy is

A

more than the weight of the seesaw

46
Q

Toss a baseball bat into the air and it wobbles about its

A

center of mass

47
Q

The famous Leaning Tower of Pisa doesn’t topple over because its center of gravity is

A

above a place of support

48
Q

The center of mass of a human body is located at a point that

A

changes as a person bends over

49
Q

To kick a football so it won’t topple end over end, kick it so the force of impact extends

A

through its center of gravity

50
Q

A 1-kg rock is suspended from the tip of a horizontal meterstick at the 0-cm mark so that the meterstick barely balances like a seesaw when its fulcrum is at the 25-cm mark. From this information, the mass of the meterstick is

A

1 kg

51
Q

You can safely stand on the overhanging end of a heavy plank that rests on a table. How much overhang depends on your mass and the plank’s mass. If you can stand on the end of a plank that overhangs the edge of the supporting table 1/4 its total length, how massive is the plank compared to your mass?

A

the same

52
Q

Centripetal force does no work on a circularly-moving object because

A

centripetal force has no component in the direction of motion

53
Q

Centrifugal forces are an apparent reality to observers in a reference frame that is

A

rotating

54
Q

Multiple the equation for linear momentum by radial distance r and you have

A

angular momentum

55
Q

If the rotational speed of a rotating habitat in space increases, the weight experienced by occupants

A

increases

56
Q

When a twirling ice skater brings her arms inward, her rotational speed

A

increases

57
Q

The chef at the infamous Fattening Tower of Pizza tosses a spinning disk of uncooked pizza dough into the air. The disk becomes wider during its flight, while its rotational speed

A

slows

58
Q

As a huge rotating cloud of particles in space gravitate together forming an increasingly dense ball, it shrinks in size and

A

rotates faster

59
Q

As the polar icecaps melt, the resulting water spreads over the entire Earth. This new mass distribution tends to make the length of a day

A

longer

60
Q 
Calculate the tension in a horizontal string that whirls a 1.5-
kg
 toy in a circle of radius 2.5 
m
when it moves at 3.5 
m/s
on an icy surface.
A

7.4 N

61
Q

Calculate the torque produced by a 48-

N force when a pipe extends the length of the wrench to 0.60 m

A

29 Nm

62
Q

Why can’t you stand with your heels and back to a wall and then bend over to touch your toes and return to your stand-up position?

A

A vertical line through the center of gravity of your body is in front of the tips of your toes, which is outside your support base.

63
Q

If a turntable’s rotational speed is doubled, then the linear speed of a pet hamster sitting on the edge of the record will

A

double

64
Q

Which of these animals has a quicker stride?

A

mouse

65
Q

Which jar will roll down an incline in the shortest time, an empty one or one filled with peanut butter?

A

filled jar

physics 1310 (17 decks)

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