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Z 2nd Exam Biomechanics > Chapter 6 PowerPoint > Flashcards

Chapter 6 PowerPoint Flashcards

1
Q

What is angular motion?

A

Rotational motion around an axis

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2
Q

Rotation is called ____ ____?

A

Rotation is called Angular motion

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3
Q

Almost all ____ movements involve rotation?

A

Almost all our/human movements involve rotation.
ie.
-Joints
-Swinging a bat or racquet
-Cars moving
-Door opening

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4
Q

Centric force?

A

Centric Force – directed through the center

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5
Q

Eccentric force?

A

Eccentric Force – away from the center

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6
Q

Torque?

A

Torque – the tendency of an eccentric force to rotate an object around an axis.
Aka moment of force or moment.

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7
Q

Axis of rotation?

A

Axis of rotation – point about which a body rotates

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8
Q

What two factors does torque depend on?

A

Torque depends on 2 factors
-Magnitude of externally applied force
-Distance the force is applied from the axis of rotation

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9
Q

Moment arm?

A

Moment Arm – perpendicular distance between the force and axis of rotation

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10
Q

What is the equation for torque?

A

T = F x r x sin Θ
T = F x d
Torque = Force x moment arm

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11
Q

Torque is a ____ quantity because it has
____ and ____?

A

Torque is a vector quantity because it has
Magnitude and Direction

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12
Q

How to define the direction of torque?

A

Torque has a Turning effect
Clockwise (-)
Counterclockwise (+)
Right hand thumb rule

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13
Q

Torque itself is not ____ or ____ it is simply a direction or sense of rotation around the defined axis?

A

Torque itself is not positive or negative it is simply a direction or sense of rotation around the defined axis

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14
Q

How to find net torque?

A

-Establish magnitude of applied force
1cm = 10N
-Find the length of moment arm by measuring perpendicular distance between axis of rotation and applied force
-Calculate torque for each force using equation
-Establish direction for each torque using the righthand rule
-Sum the torques to find the net magnitude and direction of rotation caused by torques

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15
Q

The sum of all torques equals ____?

A

The sum of all torques equals 0

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16
Q

Where is the center of mass for a symmetrical object?

A

In the center

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17
Q

What is the center of gravity?

A

Center of gravity – the point where all torques = 0

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18
Q

How does finding the center of gravity in a human work?

A

Center of Gravity in a Human
-Unequal, nonsymmetrical object
-Can’t doesn’t work the same
-Calculate mass distribution and then sum torques to 0

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19
Q

The center of gravity varies between ____–____% of standing height measured from the soles of the feet depending upon gender.

A

The center of gravity varies between 53–59% of standing height measured from the soles of the feet depending upon gender.

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20
Q

What is angular position?

A

The location of a given point based on the distance from the origin (r) and angle (theta) between the chosen reference axis the line formed by connecting the given point to the origin

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21
Q

What is angular distance?

A

Angular distance is the sum of all angular changes.

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22
Q

What are the three units for angular displacement?

A

Units: degrees, radians, or rotations

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23
Q

What is angular displacement?

A

Angular displacement is the difference between the initial and final positions

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24
Q

How is angular displacement defined?

A

Defined by both magnitude and direction
CW (-), CCW (+)
Units in Degrees, Radians, Revolutions

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25
Q

What is a radian?

A

360° /2π = 57.3° = 1 radian

The radius – half the diameter of a circle

The radian is the size of the angle subtended at the center of a circle by an arc equal in length to the radius of the circle.

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26
Q

When is the use of radians beneficial?

A

Its more convenient unit for extremely large angular distances or displacements

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27
Q

Radians are often quantified in multiples of ____?

A

Radians are often quantified in multiples of pi (π)

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28
Q

What is the conversion between degrees, radians, and revolutions?

A

90 degrees
pi/2 radians
1/4 revolution

180 degrees
pi radians
1/2 revolution

270 degrees
3pi/2radians
3/4 revolution

360 degrees
2pi radians
1 revolution

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29
Q

The rate of change in angular motion is calculated using what units?

A

The rate of change in angular motion
Units deg/s, rad/s, rev/s

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30
Q

What is angular speed?

A

Ang speed = Ang distance/ change in time
σ = ϕ / Δ t

31
Q

What is angular velocity?

A

Angular Velocity = Δ displacement/ Δ time
omega = Δ theta / Δ t
omega = pos2 – pos1/ time2 – time1

32
Q

Angular velocities at joints of throwing arms in MLB vs youth pitchers?

A

Angular velocities at joints of throwing arms in MLB:
2320deg/s in Elbow Extension
7240deg/s in Internal Rotation of shoulder
Angular Velocities at joints of youth pitchers
2330deg/sec Elbow extension
6900deg/sec Internal Rotation of shoulder

33
Q

What are the angular velocities of tennis players?

A

Trunk tilt 280deg/s
Upper torso rotation 870deg/s
Pelvic rotation 440deg/s
Elbow extension of 1510deg/s
Wrist flexion 1950deg/sec
Shoulder internal rotation
Males: 2420deg/s
Females: 1370deg/s

34
Q

The larger the ____ ____ ____, the greater the ____ ____ traveled by a point on a rotating body?

A

The larger the radius of rotation (r), the greater the linear distance (s) traveled by a point on a rotating body. s = r x phi

35
Q

A simple experiment in which a rotating stick simultaneously strikes three balls demonstrates the significance of the ____ ____ ____?

A

A simple experiment in which a rotating stick simultaneously strikes three balls demonstrates the significance of the radius of rotation.

36
Q

Angular velocity and linear velocity share the same ____ during a given ____ ____ ____?

A

Angular velocity and linear velocity share the same properties during a given instant in time

37
Q

What equation can be used to relate linear to angular velocities?

A

v = r x omega

Units in this case:
m/s = (m) (rad/s)

38
Q

The greater the ____ ____ ____ at which a swinging implement hits a ball, the greater the ____ ____ imparted to the ball?

A

The greater the radius of rotation at which a swinging implement hits a ball, the greater the linear velocity imparted to the ball

39
Q

The greater the ____ ____the farther a struck ball will travel?

A

The greater the angular velocity the farther a struck ball will travel

40
Q

Why does a bigger bat not always equal a larger distance?

A

Don’t forget that magnitude matters.
Extra long bat could be too heavy for the player.

41
Q

Describe angular acceleration?

A

Rate of change in angular velocity

Can be examined as 2 perpendicular linear acceleration components. Along and perpendicular to the path of angular motion.
Δ ang.velocity
Angular acceleration = Δ time
alpa = omega2 - omega1/ t2 – t1

Deg/s2 or Rad/s2

42
Q

What two components can angular acceleration be divided into?

A

Tangential linear accerleration
Centripetal acceleration

43
Q

What is tangential linear acceleration?

A

Tangential Linear acceleration
Linear acceleration of a point on a rotating segment

44
Q

What is centripetal acceleration?

A

Centripetal acceleration (Center Seeking)
Best Example – Swinging a rope.
Pull the rope toward the center to make it swing in a circle.

45
Q

What is the equation for tangential acceleration?

A

At: Component of acceleration of angular motion directed along a tangent to the path of motion
Represents change in linear speed
at = (v2 - v1)r / t2 – t1

aT = “Δ omega r” /”Δt” = alpha r

46
Q

The ____ the curve the harder it is to maintain a high velocity?

A

The tighter the curve the harder it is to maintain a high velocity.

47
Q

What is the equation for radial acceleration?

A

ar = vT2 / r

Ar: Component of acceleration of angular motion directed toward the center of curvature represents change in direction

48
Q

What is angular inertia?

A

Angular Inertia – The body’s tendency to resist angular motion.
Directly proportional to an objects mass
> mass = > resistance to Angular acceleration.
With respect to distribution of mass about an axis of rotation

I = mr2

I is Inertia
m is the objects mass
r is the radius of rotation
Units of Kg/m2

49
Q

What is the moment of inertia?

A

Moment of Inertia = mass* radius of gyration
I = mk2

50
Q

What is the radius of gyration?

A

Radius of gyration (k) – is the distance representing how far the mass of a ridged body would be from an axis of rotation if its mass were concentrated at one point.
Object mass distribution with respect to a given axis of rotation.
Not the same as Center of Gravity of a segment of the body.

51
Q

Why is it hard to calculate the body’s mass per segment?

A

It is impractical to attempt to calculate the body’s mass distribution per segment. Bone, muscle, fat all have unique quantities per person.

52
Q

How to set up the torque equation for a dumbell curl?

A

The sum of the torques = 0
T = Fd⊥
T = (- Fbiceps d⊥ ) + Fdumbbell d⊥ + F forearemd⊥

53
Q

What is angular momentum?

A

Quantity of angular motion possessed by a body, measured as the product of moment of inertia and angular velocity

How hard is it to stop something that is rotating?

54
Q

What is the equation for angular momentum?

A

Angular motion : L = Iω or L = mk2ω
I is moment of inertia and ω is angular velocity
Kg*m2/sec

55
Q

What three factors affect the magnitude of angular momentum?

A

3 factors affecting magnitude of angular momentum
Mass(m)
Distribution of mass w/ respect to axis (k)
Angular Velocity of body (ω)
No angular velocity = no angular momentum

56
Q

What does the conservation of angular momentum mean?

A

Conservation of angular momentum
Total angular momentum remains constant in the absence of external torques

57
Q

What is angular impulse?

A

Change in Angular Momentum
Angular impulse is the product of Torque and a time interval

58
Q

What is the equation for angular impulse?

A

Tt = Angular Impulse
T Δt = ∆ L
T Δt = (Iω)2 – (Iω)1

59
Q

As Long as the ____ ____ ____ of a rotating body remains constant, increased ____ ____ translates directly to increases ____ ____when the object is projected?

A

As Long as the moment of Inertia (mk2) of a rotating body remains constant, increased angular momentum translates directly to increases linear momentum when the object is projected

60
Q

What is rotational power?

A

Rotational power:
Pa = power; rate of work performed about an axis
Wa = rotational work performed
Δt = time interval (timefinal – timeinitial)
P = 𝑊𝑎/𝛥𝑡

61
Q

What is kinetic energy?

A

Objects in motion have the potential to perform work.

62
Q

What is rotational kinetic energy?

A

Rotational kinetic energy: energy associated with angular motion
KER = kinetic energy (energy associated with angular motion)
Ia = mass of the object in motion
a2 = angular velocity of the object in motion

KER = 1⁄2 Ia omega a2

63
Q

What is angular momentum?

A

Quantity of angular motion possessed by a body, measured as the product of moment of inertia and angular velocity
How hard is it to stop something that is rotating?

64
Q

What is rotational kinetic energy?

A

Rotational kinetic energy: energy associated with angular motion
KER = kinetic energy (energy associated with angular motion)
Ia = mass of the object in motion
a2 = angular velocity of the object in motion

KER = 1⁄2 Ia a2

65
Q

What is the principle of work and energy?

A

Principle of work and energy: the work performed by externally applied eccentric forces other than gravity causes a change in energy of the object acted upon

66
Q

The change in the sum of the ____ ____, ____ ____, ____, and ____ forms of energy produced by the application of externally applied eccentric force equals the total mechanical work performed?

A

The change in the sum of the linear kinetic, rotational kinetic, potential, and thermal forms of energy produced by the application of externally applied eccentric force equals the total mechanical work performed

W = ΔE = ΔKEL + ΔKER + ΔPE + ΔTE

67
Q

Angular equivalent to mass?

A

Mass (m)
Moment of inertia (I = mk2)

68
Q

Angular equivalent to force?

A

Force (F)
Torque (T = Fd)

69
Q

Angular equivalent to momentum?

A

Momentum (M=mv)
Angular momentum (H=mk2)

70
Q

Angular equivalent to impulse?

A

Impulse (Ft)
Angular impulse (Fd t)

71
Q

How can the principles of rotational mechanics be applied to functional anatomy?

A

Muscle force couples

72
Q

How can the princples of rotational mechanics be applied to sports science?

A

In club sports and throwing sports

73
Q

How can the principles of rotational mechanics be applied to functional anatomy?

A

Muscle force couples

Z 2nd Exam Biomechanics (3 decks)

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