Angular Kinematics - (week 25)

Question 1

state what it is meant by the key term - ‘angular motion’

Answer 1

angular kinematics is the movement that occurs around a fixed axis of rotation

Question 2

when does angular motion occur ?

Answer 2

angular motion occurs when a force is applied outside the axis of rotation

Question 3

what does not occur in angular motion ?

Answer 3

in angular motion, not all the parts of the body move the same linear distances

Question 4

most human movement is a result of angular motion. state 2 expansionary facts to this statement

Answer 4

1. rotation around a point of contact (eg - floor, bar)

2. rotation about the COM (eg - arial activities)

Question 5

finish the sentence:

rotation around joint centres is…

Answer 5

rotation around join centres is fundamentally how we move, and it causes general motion (a combination of linear and angular motion)

Question 6

in many activities, the linear properties are achieved by what ?

Answer 6

in many activities, the linear properties are achieved by interacting and often sequential angular motion (segmental rotation)

Question 7

describing angular motion can have important applications in what ?

Answer 7

describing angular motion can have important implications in for performance and injury

Question 8

describe what it is meant by the key term - ‘6 degrees of freedom’ (2 points)

Answer 8

1. 3 planes of motion = 3 ways to move linearly across a plane (translation)
2. 3 axis of rotation = 3 ways to rotate about an axis perpendicular to a plane (rotation)

Question 9

state what it is meant by the key term - vertex

Answer 9

an angle is compromised into two ‘lines’ that intersect at a point known as a ‘vertex’

Question 10

in biomechanical analysis, the intersecting lines are generally body (fill blank), and the (fill blank) a joint

Answer 10

1. segments

2. vertex

Question 11

what is the SI unit for angles / angular motion ?

Answer 11

Radians, rad(s)

Question 12

1 radian =

finish the sentence

Answer 12

1 radian = the angular distance (θ) covered when the arc length (s) equals the radius (r)

Question 13

what is the equation for Radians ?

Answer 13

degrees x (pi / 180)

Question 14

state the radian values for the following degrees: 45, 90, 180, and 360

Answer 14

45 degrees = π/4 rad
90 degrees = π/2 rad
180 degrees = π rad
360 degrees = 2π rad

Question 15

state what it is meant by the key term - absolute angles

Answer 15

the ‘absolute angle’ is the angle of inclination of a line (segment) relative to a fixed reference. it describes the orientation of a line in space

Question 16

what is the fixed reference always in angular kinematics ?

Answer 16

the ‘right horizontal’

Question 17

what is anti-clockwise and clockwise rotation ?

Answer 17

1. anti-clockwise = positive rotation

2. clockwise = negative rotation

Question 18

what do you always need to remember when working with angles !!!

Answer 18

measure proximal - distal

Question 19

what equation do you use to work out absolute angles ?

Answer 19

tan-1 (y proximal - y distal) / (x proximal - x distal)

Question 20

state what it is meant by the key term - ‘relative joint angle’

Answer 20

the relative joint angle is the angle between two lines (segments) that describes the configuration of two segments without defining the orientation of the segments in space

Question 21

what are flexion and extension typically referred to as being ?

Answer 21

1. flexion = negative

2. extension = posiitve

Question 22

what are the two methods of working out relative joint angles ?

Answer 22

1. the cosine rule

2. use the segment absolute angles

Question 23

state the cosine rule formula

Answer 23

cos(θ) = (B^2 + C^2 - A^2) / (2 x a x b)

Question 24

explain the formula for using the absolute joint angles to work out a relative joint angle

Answer 24

1. θ = 180 - θ proximal + θ distal
2. 0 degrees = full flexion
3. 180 degrees = full extension

Question 25

state what it is meant by the key term - angular displacement (degrees or rad)

Answer 25

angular displacement is the change in orientation of a segment/joint position (change in absolute or relative angle)

Question 26

what is angular displacement often referred to as ?

Answer 26

range of motion (ROM)

Question 27

what is the formula for angular displacement ?

Answer 27

angular displacement (θ) = θf - θi

Question 28

state 2 facts about segment angles in the context of angular displacement

Answer 28

1. anti-clockwise rotation = positive displacement

2. clockwise rotation = negative displacement

Question 29

state 3 facts about joint angles in the context of angular displacement

Answer 29

1. flexion ROM = negative displacement
2. extension ROM = positive displacement
3. can be relative to a joint. eg) - 50 degrees, or 50 degrees flexion

Question 30

state what it is meant by the key term - angular velocity (𝒘)

Answer 30

angular velocity (𝒘) is the rate of change in angular displacement (the slope of the angle-time curve)

Question 31

state the formula for angular velocity

Answer 31

angular velocity (𝒘) = (θf - θi) / Δt

Question 32

state 2 facts about segment angles in the context of angular velocity (𝒘)

Answer 32

1. anti-clockwise rotation = positive angular velocity

2. clockwise rotation = negative angular velocity

Question 33

state 3 facts about joint angles in the context of angular velocity (𝒘)

Answer 33

1. flexion ROM = negative angular velocity
2. extension ROM = positive angular velocity
3. can report relative to a joint. eg) - 50 rads/sec, or 50 rads/sec flexion

Question 34

what is angular velocity (𝒘) measured in ?

Answer 34

rads/sec

or, degrees/sec

Question 35

state what it is meant by the key term - angular acceleration (α)

Answer 35

angular acceleration (α) is the rate of change in angular velocity (slope of the angular velocity-time graph)

Question 36

what is angular acceleration (α) measured in ?

Answer 36

rads/sec^2

or, degrees/sec^2

Question 37

state the formula for angular acceleration (α)

Answer 37

angular acceleration (α) = (𝒘f - 𝒘i) / Δt

Question 38

what is the formula for the curvilinear distance ?

Answer 38

curvilinear distance (l) = radius x θ

Question 39

what must θ be measured in when measuring the curvilinear distance ?

Answer 39

θ must be measured in radians when measuring the curvilinear distance of something

Question 40

state what it is meant by the key term - tangential velocity

Answer 40

tangential velocity (VT) = the velocity perpendicular to the rotating object

Question 41

state the formula for tangential velocity (VT)

Answer 41

tangent velocity (VT) = radius (r) x angular velocity (𝒘)

Question 42

what does ‘angular velocity –> linear velocity’ show ?

Answer 42

the greater the radius, the greater the tangential velocity for a given angular velocity

Question 43

what is angular motion used for ?

Answer 43

angular motion is used to increase the linear velocity of an implement (eg - a gild swing)

Question 44

what does ‘angular acceleration –> linear acceleration’ show ?

Answer 44

the greater the radius, the greater the linear (tangential) acceleration for a given angular acceleration

Question 45

state the 2 formulae for tangential acceleration

Answer 45

(aT) = radius (r) x acceleration (a)

(aT) = (VT,f - VT,i) / Δt

Question 46

state what it is meant by the key term - tangential acceleration

Answer 46

tangential acceleration is the acceleration perpendicular to the rotating object (must be in rads/s^2)

Question 47

state what it is meant by the key term - centripetal/radial acceleration

Answer 47

centripetal/radial acceleration (ac) describes the acceleration towards the centre of rotation (centre-seeking)

Question 48

state the 2 formulae for centripetal/radial acceleration (ac)

Answer 48

(ac) = radius (r) x angular velocity (𝒘)^2

(ac) = VT^2 / r

Question 49

what is the cosine rule ?

Answer 49

c = root (a2+b2﹣2abcos(γ))

Question 50

state 2 additional facts about relative joint angles

Answer 50

1. Used to calculate the angle at a joint (relative angle between two segments)
2. Typically, flexion is defined as negative, extension as positive.