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1

centrifugal force

-The apparent outward force on a rotating or revolving body.
-It is an effect of rotation.
-Is fictitious because it is not part of an interaction, and therefore not a true force.
-Is due to the tendency of a moving body to move in a straight-line path.

2

What moves faster on a disk?

Inside and outside have the same rpm, but the outside part moves faster than the inside.

3

Can the terms linear speed and rotational speed be used interchangeably?

No. [see sec 10.2]

4

A satellite is...

constantly changing direction as it travels around the Earth, and so it is constantly accelerating. B/c it is accelerating, it is experiencing a net force, gravity.

5

axis

straight line around which rotation takes place

6

Two types of circular motion

Rotation and revolution

7

Rotation

motion about an axis located within the body of the object

8

internal axis

an axis located within the body of the object

9

Revolution

the motion about an axis located outside the body of an object

10

Linear speed

distance traveled per unit of time

11

Tangential speed

The speed of an object moving in a circular path. Called this because the direction of motion is always tangent to the circle.

12

Rotational speed.

aka angular speed. Number of rotations per minute (rpm).

13

A point farther away from the center travels...

...a longer path in the same time, and therefore, has a greater tangential speed.

14

tangential speed proportion

tangential speed ~ radial distance * rotational speed or v ~ r*w

15

What does tangential speed depends on?

Rotational speed and the distance from the axis of rotation

16

Why does a moving freight train stay on the tracks?

Because their rims are slightly tapered.

17

An object moving in a circle still undergoes...

...an acceleration, even at a constant speed, because its direction is changing, which is due to net force.

18

Centripetal acceleration

What any object moving in a circle undergoes an acceleration that is directed to the center of the circle.

19

Centripetal

means "toward the center."

20

What would happen if a centripetal force ceased to act on an object moving in a curved path?

the object would move in a straight line.

21

the centripetal force that holds a car in a curved path while rounding a corner comes from.

comes from the friction between the tires and the road.

22

When you are riding in a car and it goes around a sharp left-hand corner, why are you pressed against the door of the car?

There is no centripetal force acting to hold you in place.

23

What causes the centrifugal-force effect?

Inertia

24

In a rotating reference frame, what forces act on objects in the rotating system?

Both centripetal and centrifugal forces

25

Center of mass and center of gravity are...

...closely related, and for many objects, are essentially the same thing

26

Center of gravity

-The point at the center of an object's weight distribution, where the force of gravity can be considered to act.
-The lower your center of gravity, the more stable you are.

27

An object in equilibrium has...

...no net torque acting on it.

28

When would the center of gravity and the center of mass be in different locations in an object?

Possibly in a very large object when the gravity varies from one part of the object to the other.

29

An object remains in rotational equilibrium if its center of mass is...

...above the area of support

30

Torque

The rotational analog of force; the product of force and the lever arm (measured in newton-meters). Tends to produce rotational acceleration.

31

Mechanical equilibrium rotational

sigma(torques) = 0

32

What does torque produce?

Rotation

33

Lever arm

The perpendicular distance between an axis and the line of action of a force that tends to produce rotation about that axis.

34

When balanced torques act on an object...

...there is no change in rotation

35

Center of mass

The point at the center of an object's mass distribution, where all the mass can be considered to be concentrated

36

Where is center of mass located in an object?

At the point located at the object's average position of mass.

37

How to apply spin to an object

A force must be applied to the edge of the object. Produces torque -> adds rotation to projectile.

38

Center of gravity of people

Is not located in a fixed place, but depends on body orientation.

39

Change in location of CG upon toppling

The center of gravity of that object is raised, lowered, or unchanged.

40

Unstable equilibrium

The state of an object balanced so that any small displacement or rotation lowers its center of gravity.

41

Stable equilibrium

The state of an object balanced so that any small displacement or rotation raises its center of gravity.

42

Neutral equilibrium

The state of an object balanced so that any small movement neither raises nor lowers its center of gravity.

43

When will an object spin/rotate?

When a force applied to an object does not pass through the object's center of mass.

44

What happens when the CG of an object is raised?

the gravitational potential energy increases

45

Describe the conditions that are necessary so that an object will remain upright.

As long as the center of gravity of the object is above the area of support, the object will remain upright.

46

Explain the difference between stable, unstable, and neutral equilibrium.

In unstable equilibrium, the CG is lowered with displacement. In stable equilibrium the CG rises with displacement. In neutral equilibrium the CG neither rises nor falls with displacement.

47

torque equation

torque = force * lever arm
OR torque = force * distance

48

"objects in motion tend to stay in motion" must hold true for objects...

moving in circular paths as well.

49

What does inertia of a rotating object depend on?

both mass and distance

50

Major axes for human body

longitudinal, transverse, medial

51

Angular inertia

resistance to change in motion due to mass at a radial distance

52

Angular momentum equation

angular momentum = rotational inertia * rotational velocity
a = I*w
OR
angular momentum = mvr (mv = magnitude of linear momentum, r = radial distance)

53

Angular momentum

Product of rotational inertia and rotational velocity. For rotating objects. Conserved when no net torque acts on object

54

Rotational inertia

-aka moment of inertia.
-The resistance of an object to changes in its rotational motion.
-Is determined by the distribution of the mass of the object and the location of the axis of rotation or revolution.

55

The greater an object's rotational inertia the more difficult it...

...is to change the rotational speed of an object.

56

Rotational inertia equation

I = mr^2 where I = rotational inertia, mass m is concentrated at the same distance r from a rotational axis

57

Longitudinal axis

Head-to-toe axis

58

Transverse axis

Rotate about it when perform somersault or flip

59

Media axis

Front-to-back axis

60

Objects of the same shape but different sizes accelerate...

equally when rolled down an incline. a = F/m

61

Linear momentum

Product of mass and velocity of an object. aka momentum.

62

Rotational velocity

Rotational speed together with a direction for the axis of rotation or revolution. Is a vector quantity with the same direction as angular momentum.

63

Newton's first law of inertia for rotating systems

An object or system of objects will maintain its angular momentum (continue rotating about axis) unless acted upon by an unbalanced external torque.

64

Law of conservation of angular momentum

An object or system of objects will maintain a constant angular momentum unless acted upon by an unbalanced net torque.

65

What can simulate gravity?

In a rotating frame of reference, there seems to be an outwardly directed centrifugal force, which can simulate gravity.

66

What is inertia a measure of?

Laziness

67

What direction, when a person is in a large rotating space, is the "up" direction that a person senses is toward

the center of rotation

68

Equation for rotational inertia, I, of a solid sphere spinning about its axis of rotation?

l = (2/5)m*r^2

69

Does a hoop or a solid disk of the same diameter have a greater acceleration for down an incline?

The solid disk because it has less rotational inertia per mass.

70

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.

71

Centripetal Force

-Center-directed force that causes an object to move in a curved (sometimes circular) path.
-Not basic forces of nature.
-Equation: (mass*tangential speed^2)/(radius of curvature
or
F(c) = (mv^2)/r