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Physics 130: Lecture Slide (Chapter Review) > Chapter 8: Rotational Motion (from Lecture Slide) > Flashcards

Chapter 8: Rotational Motion (from Lecture Slide) Flashcards

1
Q

When an object turns about an internal axis, it is undergoing

A

Circular motion or rotation

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2
Q

Circular motion is characterized by two kinds of speeds

A

1) Tangential (linear) speed
2) Rotational (angular) speed

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3
Q

Rotational speed is

A

The number of rotations or revolutions per unit of time

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4
Q

All parts of a rigid turntable turn about the axis of rotation in

A

The same amount of time

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5
Q

All points have the same

A

Angular/rotational speed

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6
Q

Tangential speed

A

The linear speed of something moving along a circular path

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7
Q

At different radii, the tangential speeds

A

Can be vary

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8
Q

Rotational inertia

A

The property of an object to resist changes in its rotational state of motion

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9
Q

An object rotating about an axis tends to remain rotating about

A

The same axis at the same rotational speed unless interfered with by some external influence

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10
Q

Bodies that are rotating tend to remain what?

A

Rotating

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11
Q

Non-rotating bodies tends to remain what?

A

Non-rotating

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12
Q

Like linear rotation, rotational inertia depends on

A

Mass: Distribution of the mass about the axis of rotation

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13
Q

The greater the distance between an object’s mass concentration and the axis

A

The greater the rotational inertia

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14
Q

The greater the rotational inertia of an object

A

The greater the difficulty in changing its rotational state

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15
Q

Much of the mass of the pole is far from

A

The axis of rotation (its midpoint)

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16
Q
  1. Depends upon the axis around which it rotates
A

a. Easier: to rotate around an axis passing through it (mass is evenly distributed around axis)

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17
Q
  1. Depends upon the axis around which it rotates
A

b. Harder: to rotate it around vertical axis passing through center (half of its mass is distributed on both sides of the axis)

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18
Q
  1. Depends upon the axis around which it rotates
A

c. Hardest: to rotate it around vertical axis passing through the end (all mass is on one side of the axis)

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19
Q

Torque is

A

The rotational counterpart of force

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20
Q

Force tends to

A

Change the motion of things

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21
Q

Torque depends upon three factors:

A

1) Magnitude of the force
2) The direction in which the force acts
3) The point at which the force is applied on the object

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22
Q

Torque (like rotational inertia) involves distance from the rotational axis. This distance is called the

A

Lever arm

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23
Q

The tendency of a force to cause rotation is called

A

Torque

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24
Q

Lever arm is less than

A

Length of handle because of direction of force

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25
Q

Lever arm is equal to

A

Length of handle

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26
Q

Lever arm is longer than

A

Length of handle

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27
Q

If the force is applied in the same direction as the perpendicular distance or at the axis of rotation, which force produces no torque?

A

It does not rotating anything

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28
Q

If the seesaw doesn’t rotate, does that mean that there’s no torque?

A

Like Newton 1st law, you can still have force but have zero net force

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29
Q

Similarly, you can still have torques, produces but having what?

A

Zero net torque

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30
Q

Center of mass

A

The average position of all the mass that makes up the object

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31
Q

Symmetric object, the mass is located at

A

The geometric center

32
Q

Asymmetric (irregular) object depends on

A

The position, bat, were thicker end

33
Q

Center of gravity

A

The average position of weight distribution and located at the same point as the CM

34
Q

Two types of motion

A

1) Straight line motion along its CM
2) Rotation about its CM

35
Q

Locating the center of gravity

A

1) Is at geometric midpoint
2) Balancing objects provides a way to find CG
3) All points produce a resultant weight vector at the CG
4) Supporting the midpoint supports the entire stick

36
Q

Stability

A

The location of the center of gravity is important for stability

37
Q

If we draw a line straight down from the center of gravity and it falls

A

Inside the base of support of the object, it is in stable equilibrium and it will balance.

38
Q

If it falls outside the base, it is

A

Unstable

39
Q

Both L-shaped objects have the same weight. Are they in equilibrium?

A

A torque exists in both and their line of gravity falls outside the base of support, so they tend to rotate, both are unstable and both fall over

40
Q

Centripetal force

A

Any force directed toward a fixed center

41
Q

Centripetal means

A

Center-seeking or toward the center

42
Q

Centripetal force depends upon

A

1) Mass of object
2) Tangential speed of the object
3) Radius of the circle

43
Q

Centripetal force deals with any force that is

A

Directed towards the center

44
Q

If the motion is circular and at constant speed, this force is

A

At right angle, to the path of the moving object

45
Q

Greater speed and greater mass require

A

Greater centripetal force

46
Q

Traveling in a circular path with a smaller radius of curvature requires

A

A greater centripetal force

47
Q

When a car rounds a curve, the centripetal force prevents it from

A

Skidding off the road (friction force)

48
Q

If the road is wet, or if the car is going too fast, the centripetal force is

A

Insufficient to prevent skidding off the road

49
Q

Only two forces act on the bob

A

1) mg, the force due to gravity
2) T, tension in the string

50
Q

Net force in the vertical direction of the centripetal force is

A

Zero

51
Q

Vertical direction must be

A

Equal and opposite to mg

52
Q

Horizontal force is the net force on the bob that contributes to the

A

Centripetal force

53
Q

Although centripetal force is center directed, an occupant inside a rotating system seems to

A

Experience an outward force

54
Q

This apparent outward force on a rotating or revolving body is called

A

Centrifugal force

55
Q

Centrifugal means

A

Center-fleeing or away from the center

56
Q

It is misconception that a centrifugal force pulls

A

Outward on an object

57
Q

If the string break, the object doesn’t move

A

Radially outward

58
Q

If the string break, It continues along its tangent straight-line path, because what?

A

No force acts on it (Newton’s First Law of Inertia)

59
Q

Centrifugal force sometimes called what?

A

1) Fictitious force
2) Apparent force
3) Inertial force

60
Q

Centrifugal force is not a real force like gravity, but

A

In a rotating frame, the centrifugal force feels like a real force

61
Q

Centrifugal force with free fall

A

They don’t feel gravity anymore but they feel simulated gravity.

62
Q

Simulated gravity: Stationary frame (outside)

A

1) Action-reaction pair between floor and person
2) If the system is defined on, the reaction froce of the floor contributes to the centripetal force

63
Q

Simulated force: Rotating frame (inside)

A

1) No action-reaction pair exist
2) Centrifugal force acts at the center of gravity of it
3) Nothing that pulls back on it

64
Q

Linear momentum

A

Motion along a straight line path, and called: “Inertia of motion”

65
Q

Angular momentum

A

The “inertia of motion” of rotating objects

66
Q

Angular momentum (point-like masses)

A

Object that is small compared with the radial distance to its axis of rotation

67
Q

Rotational version of Newton’s first law: An object or system of objects will:

A

Maintain its angular momentum unless acted upon by an external net torque

68
Q

An external net torque is required to

A

Change the angular momentum of an object

69
Q

Our solar system has angular momentum that includes the Sun:

A

The spinning and orbiting planets and other smaller bodies

70
Q

The angular momentum of the solar system is

A

Conserved unless an external torque outside the solar system changes it

71
Q

In the absence of net external torques, angular momentum is

A

Conserved

72
Q

In the absence of net external forces, linear momentum is

A

Conserved

73
Q

If no external net torque acts on a rotating system,

A

The angular momentum of that system remains constant

74
Q

When the man pulls the weights inward, his rotational speed

A

Increases

75
Q

Suppose by pulling the weight inwards, the rotational inertia of the man reduces to

A

Half its value and the factor that would angular velocity change is double!

Physics 130: Lecture Slide (Chapter Review) (23 decks)

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