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EXS 385: Biomechanics > The Conditions of Rotary Motion > Flashcards

The Conditions of Rotary Motion Flashcards

1
Q

A force whose direction is not in line with either the center of gravity of a freely moving object or the center of rotation of an object with a fixed axis of rotation.

A

Eccentric force

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2
Q

The turning effect of an eccentric force

A

Torque

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3
Q

Torque = ___________ x ________

A

magnitude of the force; length of the moment arm

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4
Q

The perpendicular distance from the line of force to the axis of rotation

A

Moment arm

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5
Q

As the moment arm decreases, the torque ____________

A

decreases

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6
Q

As the magnitude of the force decreases, the torque ___________

A

decreases

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7
Q

True or False: In the human body, the weight of a segment can be altered simultaneously.

A

False, the weight of a body segment CANNOT be altered simultaneously

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8
Q

The torque of a segment due to gravity can be changed only by changing the ______ __ ___ ________ ___.

A

length of the moment arm

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9
Q

Muscle forces that exert torque are dependent on which two things?

A

Point of insertion of the muscle
Changes in length, tension, and angle of pull

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10
Q

Only the rotary/stabilizing component of the muscle force vector is actually a factor in torque production.

A

rotary

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11
Q

The rotary/stabilizing component of the muscle force vector acts along the mechanical axis of the bone through the axis of rotation.

A

stabilizing

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12
Q

True or false: the stabilizing component of the muscle force is not eccentric.

A

True

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13
Q

Once a muscle force is resolved into a rotary and stabilizing component, the moment arm is the distance between the ____________ and the ________________

A

axis of rotation
point of application of the rotary component of the muscle force

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14
Q

Equal parallel eccentric forces applied in the same direction on opposite sides of the center of rotation will initiate _______ motion.

A

Linear; no

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15
Q

Equal parallel forces applied in opposite directions on opposite sides of the center of rotation will initiate _______ motion.

A

rotary

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16
Q

The effect of equal parallel forces acting in opposite directions

A

force couple

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17
Q

The Principle of the Summation of Torques

A

The resultant torque of a force system must be equal to the sum of the torques of the individual forces of the system about the same point.

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18
Q

Clockwise torques are positive/negative.

A

negative

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19
Q

Lever

A

A rigid bar that can rotate about a fixed point when a force is applied to overcome a resistance

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20
Q

What are the two functions of a lever?

A

1.) Overcome a resistance larger than the magnitude of the effort applied
2.) Increase the speed and range of motion through which a resistance can be moved

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21
Q

When there is no motion, the torque produced by effort and the torque produced by resistance are _______, making the lever system _________.

A

equal; balanced

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22
Q

What are the three main purposes of external levers?

A

1.) Small force overcomes large resistance
2.) Large range of motion overcomes small resistance
3.) Balance force and load

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23
Q

True or false: Nearly every bone is a lever

A

True

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24
Q

Portion of lever between fulcrum and force application

A

Lever arm

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25
Q

The effort arm is the perpendicular distance between the fulcrum and the ________ __ _______ __ ______.

A

line of force of effort

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26
Q

The resistance arm is the perpendicular distance between the fulcrum and the _______ __ __________ _____

A

line of resistance force

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27
Q

In a ______-______ lever, the axis lies between the effort and the resistance.

A

first-class

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28
Q

In a first-class lever, if EA = RA, then the lever is used to ____________.

A

Balance two or more forces

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29
Q

In a first-class lever, if EA > RA, then the lever favors ______________

A

force production

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30
Q

In a first-class lever, if RA > EA, then the lever favors _____________

A

speed and range of motion

31
Q

Example of an anatomical first-class lever

A

Head tipping forward and backward

32
Q

In a ________-_______ lever, the main function is force production at the cost of range of motion.

A

second-class

33
Q

In a second-class lever, the EA is greater/less than the RA.

A

Greater

34
Q

Example of an anatomical second-class lever..

A

Forearm in slow downward extension

35
Q

In a _______-______ lever, the main function is speed and range of motion at the cost of needing a greater effort to overcome resistance

A

third-class

36
Q

In a third-class lever, the EA is greater/less than the RA

A

Less

37
Q

Example of an anatomical third-class lever

A

Forearm flexed by biceps and brachialis; arm abducted by deltoid muscle

38
Q

Four functions of a simple machine:

A

1.) Balance two or more forces
2.) Favor force production
3.) Favor speed and range of motion
4.) Change the direction of the applied force

39
Q

A lever of any class will balance when __________.

A

E x EA = R x RA

40
Q

When a lever has an EA longer than its RA, it favors ____________.

A

force

41
Q

When a lever has an RA longer than its EA, it favors _____________.

A

Speed and range of motion

42
Q

True or false: In angular movements, speed and range are interdependent.

A

True

43
Q

The EAs in the skeletal lever systems of the human body are determined by the _____________________ and the ___________________.

A

point of muscle attachment
muscle angle of pull

44
Q

Anatomical levers tend to favor ______________ at the expense of _______.

A

speed and range of motion
effort

45
Q

Short levers enhance ____________ ________ while sacrificing _____ ______ and ________ __ _______

A

angular velocity
linear speed, range of motion

46
Q

Strength needed to maintain angular velocity increases/decreases as the lever lengthens

A

increases

47
Q

The ability to magnify force

A

Mechanical Advantage

48
Q

The mechanical advantage of a lever is the ratio of _______________ overcome to ________ applied.

A

resistance; effort

49
Q

9 questions that should be answered for every lever:

A

1.) Where are the fulcrum, effort application, and resistance application?
2.) At what angle is the effort applied to the lever?
3.) At what angle is the resistance applied to the lever?
4.) What is the EA of the lever?
5.) What is the RA of the lever?
6.) What are the relative lengths of the EAs and RAs?
7.) What kind of movement does this lever favor?
8.) What is the mechanical advantage?
9.) What class of lever is this?

50
Q

A body continues in a state of rest or uniform rotation about its axis unless acted upon by an __________ _____.

A

external force

51
Q

The acceleration of a rotating body is directly/indirectly proportional to the torque causing it, is in the same/different direction as the torque, and is inversely proportional to the moment of inertia of the body

A

directly
same

52
Q

When a torque is applied by one body to another, the second body will exert an ______ and __________ torque on the first.

A

equal, opposite

53
Q

As the distance between the axis and the mass increase, inertia increases/decreases

A

increases

54
Q

The moment of inertia depends on _________ and ________.

A

quantity of the rotating mass
mass’s distribution around the axis of rotation

55
Q

What is the moment of inertia?

A

The size of angular inertia

56
Q

Moment of inertia equation

A

I = Σmr²

57
Q

If the mass of an object is concentrated close to the axis of rotation, the object is easier/harder to turn because the radius for each particle is more/less

A

easier
less

58
Q

True or false: Body position has no effect on mass distribution, and therefore no effect on inertia

A

False

59
Q

Which has greater inertia? A tuck or a pike?

A

A pike

60
Q

What is the angular equivalent of linear force?

A

Torque

61
Q

What is the angular equivalent of mass?

A

Moment of inertia

62
Q

What is the angular equivalent of linear acceleration?

A

Angular acceleration

63
Q

Torque equation

A

T = Iα

64
Q

Angular momentum equation

A

Angular momentum = Iω

65
Q

Law of Conservation of Angular Momentum

A

The total angular momentum of a rotating body will remain constant unless acted upon by external torques.

66
Q

When an ice skater spins, bringing her arms closer to the axis of rotation, the moment of inertia increases/decreases about that axis.

A

decreases

67
Q

True or false: A force that causes a change in angular momentum must have an equal and opposite force creating an equal and opposite momentum change

A

True (Newton’s Third Law)

68
Q

The angular velocity of two moving parts is inversely proportional to their _________ __ ______ about the axis of motion.

A

Moments of inertia

69
Q

True or False: For every angular action in a plane, the reactions must be in the same or parallel planes.

A

True

70
Q

Centripetal Force

A

A constant center-seeking force that acts to move an object tangent (at right angles) to the direction in which it is moving at any instant, thus causing it to move in a circular path

71
Q

Centrifugal Force

A

Outward-pulling force working on a body moving around a center, arising from the body’s inertia

72
Q

Centrifugal force is equal in magnitude to _____________.

A

centripetal force

73
Q

Equation for centripetal force:

A

F꜀ = mv²/r

74
Q

When a runner turns a tight corner, as centripetal force increases, the amount of lean will have to increase/decrease.

A

increase

EXS 385: Biomechanics (9 decks)

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