biomechanics: angular kinematics

what type of motion occurs within the body?

angular, there is not such thing as liner motion in the body. all body motions happen around an axis of rotation

what are the two things we must know when dealing with angular kinematics?

1. where the axis of rotation is
2. how long the radius is

what is an angle?

it is the intersection of two lines, planes, or a line and a plane (relationship of two vectors)

what is an absolute angle?

angle of a single body segment, relative to a right line

what is a relative angle?

angle of one segment relative to another

what quantity (relative or absolute angle) is used in biomechanics?

realtive

what makes measuring joint angles difficult?

they have a migrating axis of rotation

what 3 movements are possible at a joint and contribute to the migrating axis of rotation?

1. roll/rock
2. slide/glide
3. spin

what is an example of a spin movement within a joint?

the screw home mechanism

what does arthrokinematics discover?

how the surface of one bone moves relative to the surface of another bone

what are the units for angular measure?

revolutions, degrees, and radians

what is a radian?

it is a ratio of the arc length to a radius

what is a unit of angular measurement equivalent to the angle between two radii that enclose a section of a circle's circumference arc equal in length to the length of a radius

a radian

how many degrees are in a radian?

1rad=57.3deg

how many radians are in a circle?

2pi

what are the linear and angular formulas for displacement?

linear: s=p2-p1
angular: theta=p2-p1

what are the linear and angular formulas for velocity?

linear: v= (s2-s1)/(t2-t1)
angular: omega= (theta2-theta1)/(t2-t1)

what are the linear and angular formulas for acceleration?

linear: a=(v2-v1)/(t2-t1)
angular: alpha= (omega2-omega1)/(t2-t1)

what does a negative angle in angular joint kinematics indicate?

that flexion has occurred

what does a positive angle in angular joint kinematics indicate?

that extension has occurred

T/F any dot on a vector relative to another dot will rotate the same distance (aka have the same angular distance)

true

T/F any dot on a vector relative to another dot will have the same linear velocity

false. they will have the same angular velocity though because they are both going through the same angle and they both take the same amount of time.

T/F any dot on a vector relative to another dot will have the same linear distance

false. the dot that is further along on the vector has a longer radius and thus a longer distance

what is the equation relating linear and angular displacement?

s=(theta)(r)

what is the equation relating the linear and angular tangential velocity?

v=(omega)(r)

a 1.12m golf club is swung with an angular velocity of 2745deg/s. what is the linear velocity of the club head?

53.65rad/s

a pitcher releases a ball at 41.13m/s. if he is rotating the shoulder at 2983.22rad/s, how long is his arm?

.0138m

what is angular acceleration?

the rate of change of angular velocity

what are the two types of angular acceleration?

radial (centripetal)
tangential (normal)

which type of angular acceleration is directed towards the center of an object moving along a curved path?

radial acceleration

which type of acceleration represents a change in direction?

radial acceleration

in radial acceleration V remains constant with a constant what?

omega

which type of angular acceleration represents the change in linear velocity for a body traveling on a curved path?

tangential acceleration

which type of angular acceleration is directed perpendicular to the path?

tangential acceleration

what is the formula for tangential acceleration?

alpha(t)= (r)(alpha)

what is the formula for radial acceleration?

alpha(r)=v^2/r

2 runners are racing around a circular track. runner 1's lane has a radius of 15m, while runner 2's lane has a radius of 12m. if both runners have a linear velocity of 10m/s, who has more radial acceleration? what does this mean?

runner 2 does. this means that runner 2 has more tangential and less radial acceleration

why do 200 and 400m heats award the middle lanes to the fastest times?

because there is less of a shift from tangential to radial acceleration and so they are able to maintain a higher speed with tangential acceleration because there is less change in direction (radial acceleration)

what type of problem starts and finishes at the same height?

type 1

what type of problem ends higher than it starts?

type 4

what type of problem starts higher than it finishes but has a initial vertical velocity of 0?

type 2

what type of problem starts higher than it finishes and has an initial vertical velocity?

type 3

does mass matter when dealing with kinematics?

no, only matters when dealing with kinetics (force)