# Unit 4 Flashcards

1
Q

centrifugal force

A
• 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
Q

What moves faster on a disk?

A

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

3
Q

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

A

No. [see sec 10.2]

4
Q

A satellite is…

A

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
Q

axis

A

straight line around which rotation takes place

6
Q

Two types of circular motion

A

Rotation and revolution

7
Q

Rotation

A

motion about an axis located within the body of the object

8
Q

internal axis

A

an axis located within the body of the object

9
Q

Revolution

A

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

10
Q

Linear speed

A

distance traveled per unit of time

11
Q

Tangential speed

A

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

12
Q

Rotational speed.

A

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

13
Q

A point farther away from the center travels…

A

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

14
Q

tangential speed proportion

A

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

15
Q

What does tangential speed depends on?

A

Rotational speed and the distance from the axis of rotation

16
Q

Why does a moving freight train stay on the tracks?

A

Because their rims are slightly tapered.

17
Q

An object moving in a circle still undergoes…

A

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

18
Q

Centripetal acceleration

A

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

19
Q

Centripetal

A

means “toward the center.”

20
Q

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

A

the object would move in a straight line.

21
Q

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

A

comes from the friction between the tires and the road.

22
Q

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?

A

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

23
Q

What causes the centrifugal-force effect?

A

Inertia

24
Q

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

A

Both centripetal and centrifugal forces

25
Q

Center of mass and center of gravity are…

A

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

26
Q

Center of gravity

A
• 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
Q

An object in equilibrium has…

A

…no net torque acting on it.

28
Q

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

A

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

29
Q

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

A

…above the area of support

30
Q

Torque

A

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

31
Q

Mechanical equilibrium rotational

A

sigma(torques) = 0

32
Q

What does torque produce?

A

Rotation

33
Q

Lever arm

A

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

34
Q

When balanced torques act on an object…

A

…there is no change in rotation

35
Q

Center of mass

A

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

36
Q

Where is center of mass located in an object?

A

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

37
Q

How to apply spin to an object

A

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

38
Q

Center of gravity of people

A

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

39
Q

Change in location of CG upon toppling

A

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

40
Q

Unstable equilibrium

A

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

41
Q

Stable equilibrium

A

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

42
Q

Neutral equilibrium

A

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

43
Q

When will an object spin/rotate?

A

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

44
Q

What happens when the CG of an object is raised?

A

the gravitational potential energy increases

45
Q

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

A

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

46
Q

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

A

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
Q

torque equation

A

torque = force * lever arm

OR torque = force * distance

48
Q

“objects in motion tend to stay in motion” must hold true for objects…

A

moving in circular paths as well.

49
Q

What does inertia of a rotating object depend on?

A

both mass and distance

50
Q

Major axes for human body

A

longitudinal, transverse, medial

51
Q

Angular inertia

A

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

52
Q

Angular momentum equation

A

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

53
Q

Angular momentum

A

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

54
Q

Rotational inertia

A
• 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
Q

The greater an object’s rotational inertia the more difficult it…

A

…is to change the rotational speed of an object.

56
Q

Rotational inertia equation

A

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

57
Q

Longitudinal axis

A

58
Q

Transverse axis

A

Rotate about it when perform somersault or flip

59
Q

Media axis

A

Front-to-back axis

60
Q

Objects of the same shape but different sizes accelerate…

A

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

61
Q

Linear momentum

A

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

62
Q

Rotational velocity

A

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
Q

Newton’s first law of inertia for rotating systems

A

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

64
Q

Law of conservation of angular momentum

A

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

65
Q

What can simulate gravity?

A

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

66
Q

What is inertia a measure of?

A

Laziness

67
Q

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

A

the center of rotation

68
Q

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

A

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

69
Q

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

A

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

70
Q

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

A

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
Q

Centripetal Force

A

-Center-directed force that causes an object to move in a curved (sometimes circular) path.
-Not basic forces of nature.