Flashcards in Unit 4 Deck (71)

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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