Chapter 8: Rotational Motion (from Lecture Slide)

Question 1

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

Answer 1

Circular motion or rotation

Question 2

Circular motion is characterized by two kinds of speeds

Answer 2

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

Question 3

Rotational speed is

Answer 3

The number of rotations or revolutions per unit of time

Question 4

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

Answer 4

The same amount of time

Question 5

All points have the same

Answer 5

Angular/rotational speed

Question 6

Tangential speed

Answer 6

The linear speed of something moving along a circular path

Question 7

At different radii, the tangential speeds

Answer 7

Can be vary

Question 8

Rotational inertia

Answer 8

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

Question 9

An object rotating about an axis tends to remain rotating about

Answer 9

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

Question 10

Bodies that are rotating tend to remain what?

Answer 10

Rotating

Question 11

Non-rotating bodies tends to remain what?

Answer 11

Non-rotating

Question 12

Like linear rotation, rotational inertia depends on

Answer 12

Mass: Distribution of the mass about the axis of rotation

Question 13

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

Answer 13

The greater the rotational inertia

Question 14

The greater the rotational inertia of an object

Answer 14

The greater the difficulty in changing its rotational state

Question 15

Much of the mass of the pole is far from

Answer 15

The axis of rotation (its midpoint)

Question 16

1. Depends upon the axis around which it rotates

Answer 16

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

Question 17

2. Depends upon the axis around which it rotates

Answer 17

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

Question 18

3. Depends upon the axis around which it rotates

Answer 18

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

Question 19

Torque is

Answer 19

The rotational counterpart of force

Question 20

Force tends to

Answer 20

Change the motion of things

Question 21

Torque depends upon three factors:

Answer 21

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

Question 22

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

Answer 22

Lever arm

Question 23

The tendency of a force to cause rotation is called

Answer 23

Torque

Question 24

Lever arm is less than

Answer 24

Length of handle because of direction of force

Question 25

Lever arm is equal to

Answer 25

Length of handle

Question 26

Lever arm is longer than

Answer 26

Length of handle

Question 27

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

Answer 27

It does not rotating anything

Question 28

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

Answer 28

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

Question 29

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

Answer 29

Zero net torque

Question 30

Center of mass

Answer 30

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

Question 31

Symmetric object, the mass is located at

Answer 31

The geometric center

Question 32

Asymmetric (irregular) object depends on

Answer 32

The position, bat, were thicker end

Question 33

Center of gravity

Answer 33

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

Question 34

Two types of motion

Answer 34

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

Question 35

Locating the center of gravity

Answer 35

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

Question 36

Stability

Answer 36

The location of the center of gravity is important for stability

Question 37

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

Answer 37

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

Question 38

If it falls outside the base, it is

Answer 38

Unstable

Question 39

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

Answer 39

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

Question 40

Centripetal force

Answer 40

Any force directed toward a fixed center

Question 41

Centripetal means

Answer 41

Center-seeking or toward the center

Question 42

Centripetal force depends upon

Answer 42

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

Question 43

Centripetal force deals with any force that is

Answer 43

Directed towards the center

Question 44

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

Answer 44

At right angle, to the path of the moving object

Question 45

Greater speed and greater mass require

Answer 45

Greater centripetal force

Question 46

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

Answer 46

A greater centripetal force

Question 47

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

Answer 47

Skidding off the road (friction force)

Question 48

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

Answer 48

Insufficient to prevent skidding off the road

Question 49

Only two forces act on the bob

Answer 49

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

Question 50

Net force in the vertical direction of the centripetal force is

Answer 50

Zero

Question 51

Vertical direction must be

Answer 51

Equal and opposite to mg

Question 52

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

Answer 52

Centripetal force

Question 53

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

Answer 53

Experience an outward force

Question 54

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

Answer 54

Centrifugal force

Question 55

Centrifugal means

Answer 55

Center-fleeing or away from the center

Question 56

It is misconception that a centrifugal force pulls

Answer 56

Outward on an object

Question 57

If the string break, the object doesn't move

Answer 57

Radially outward

Question 58

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

Answer 58

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

Question 59

Centrifugal force sometimes called what?

Answer 59

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

Question 60

Centrifugal force is not a real force like gravity, but

Answer 60

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

Question 61

Centrifugal force with free fall

Answer 61

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

Question 62

Simulated gravity: Stationary frame (outside)

Answer 62

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

Question 63

Simulated force: Rotating frame (inside)

Answer 63

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

Question 64

Linear momentum

Answer 64

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

Question 65

Angular momentum

Answer 65

The "inertia of motion" of rotating objects

Question 66

Angular momentum (point-like masses)

Answer 66

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

Question 67

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

Answer 67

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

Question 68

An external net torque is required to

Answer 68

Change the angular momentum of an object

Question 69

Our solar system has angular momentum that includes the Sun:

Answer 69

The spinning and orbiting planets and other smaller bodies

Question 70

The angular momentum of the solar system is

Answer 70

Conserved unless an external torque outside the solar system changes it

Question 71

In the absence of net external torques, angular momentum is

Answer 71

Conserved

Question 72

In the absence of net external forces, linear momentum is

Answer 72

Conserved

Question 73

If no external net torque acts on a rotating system,

Answer 73

The angular momentum of that system remains constant

Question 74

When the man pulls the weights inward, his rotational speed

Answer 74

Increases

Question 75

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

Answer 75

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