Final Prep

Question 1

Define system

Answer 1

body/group of bodies whose motion is studied

Question 2

Define internal and external forces

Answer 2

internal=forces acting within system external = forces acting between system and environment Need external forces to move a system

Question 3

How do you measure length, mass, density, and COM

Answer 3

length/volume = cadavers, fluid displacement (V), living subjects mass = cadavers density = calculations, cadavers COM = computer modeling, radioisotope scanning, cadaversq

Question 4

Describe the 2 frames of reference

Answer 4

Absolute = environment stationary relative to frame of reference object moves relative to frame of reference Relative = object stationary relative to frame of reference environment moves relative to frame of reference

Question 5

What are typical assumptions of torque calculations

Answer 5

One muscle moment arm of muscle estimated segments rigid all muscles have same insertion point

Question 6

How can we collect data?

Answer 6

Velocity –> photos/video (cannot get it at exact times, sampling frequency may be poor) motion capture –> record body landmarks (active = sensors emit, wires, but record individual markers) (passive = sensors reflect, no wires, can’t record individual markers) Acceleration = accelerometers, force plates

Question 7

List some errors

Answer 7

Sampling frequency = poor differentiation, not sampled enough aliasing error = not sampled enough, so misinterpret data Noise = electrical interference (60Hz AC), vibration of markers on skin, vibration of sensors Use 60Hz filter to remove electrical interference, place markers on bony landmarks, isolate sensors, use low-pass filter to reduce high frequency vibration noise Differentiation = amplified by noise

Question 8

How do you increase speed?

Answer 8

below 7m/s increase stride length, above 7m/s increase stride frequency

Question 9

Describe the types of angles

Answer 9

Absolute angles = relative to external frame of reference

Relative = with respect to relative frame of reference

Degrees of flexion = distance from anatomical position

joint angles = angle of articulation between limb segments

Question 10

Metatarsal-phalangeal

Rostral angle

Answer 10

Metatarsal-phalangeal = metatarsal - phalangeal

-ve = toes up

+ve = toes down

Rostral angle = 180 - (metatarsal-phalangeal)

Question 11

Ankle angle

Answer 11

shank - metatarsal + 90

+ve = plantarflexed

-ve = dorsiflexed

Question 12

Describe the joint v time graphs

Answer 12

Question 13

Rearfoot angle

Answer 13

Shank angle - calcaneous angle

+ve = supination

-ve = pronation

Question 14

Describe RF angle during gait

Answer 14

sup-pro-sup

looks like a soup bowl graph

Question 15

What is the Q angle?

Answer 15

can result in patellar pain

pull of quad muscles - axis of leg bisecting patella

lateral pull on patella from quads

Question 16

wrist pain

Answer 16

avoid radial or ulnar deviation

avoid prolonged extension –> leads to carpal tunnel

force from wrist tendon on carpal tunnel

Bend tool to keep hand in neutral position

Question 17

Neck pain

Answer 17

overextension of neck relative to spine, even if absolute neck is neutral

Question 18

What are Newton’s laws

Answer 18

Object in motion/rest stays at constant velocity unless acted on by external force

Change in motion of object proportional to net force acting on object, and occurs in same direction as force

For every force applied by one body on a second, the seond body applies equal and oppositely directed force on first

Question 19

Maximize amount of mass moved, linear velocity, and energy

Answer 19

mass = maximize instantaneous force

linear velocity = maximize impulse/time

energy = maximize distance force is applied over

Question 20

How do you measure forces

Answer 20

force plates

via muscle tendon attached to strain gauge

artificial joints

Question 21

Describe forces during walking/running

Answer 21

running is much larger forces over smaller times. has double peak, 3-5x body weight

walking cycle much longer, only 1-1.2x body weight, smooth

Question 22

Describe different running styles

Answer 22

heel strike = double peak

midfoot or forefoot striking = smooth hill

Question 23

Friction types

no applied force

applied force < Fmaxstatic

applied force = Fmaxstatic

applied force > Fmaxstatic

Answer 23

none = no friction, no motion

< Fmaxstatic = small static friction, no motion

= Fmaxstatic = max static, no motion

> Fmaxstatic = no static, but kinetic, motion

Question 24

Why do cyclists lean, why do we bank trank

Answer 24

Cyclists lean to produce opposing torque to avoid being tilted outwards

bank track so that Fc can be increased, not all from Ff, some from Fn so can increase velocity

Question 25

How does protection work?

Answer 25

increases distance force applied over, increases time force applied over, increases area momentum, work, force constant, so decrease force/pressure

Question 26

What is the centre of mass

Answer 26

Point around which mass is equally distributed Point where the sum of torques = 0

Question 27

Describe the reaction board method

Answer 27

Weigh subject. Take reading of empty board to try to find torque due to board, but don't know board's center of mass. Will use this as the variable that is constant between equations. Then weigh subject on board, substitute in first reading for board, can then figure out subject's COM.

Question 28

Calculate centre of mass

Answer 28

sum of torques = torque of sum Can't do = 0 because that would require knowledge of the direction of torques

Question 29

How do you increase stability?

Answer 29

Increase size of BOS Lower COG Increase mass Change position of COG

Question 30

Why do we see more knee flexion during sprinting compared to walking?

Answer 30

Knee flexion decreases the moment of inertia, so the leg can rotate around faster, increasing stride frequency and therefore velocity

Question 31

Define Newton's laws for Angular Forces

Answer 31

1) Object moves with constant angular momentum unless acted on by external torque 2) Change in angular momentum proportional to net torque acting on the object, and occurs in the same direction as the external torque 3) Object applying torque on second object, second object applies torque on first object in equal magnitude, opposite direction

Question 32

Why don't bikes fall over? Kinetic chain Long jump: hang and windmill methods Cat turning

Answer 32

CONSERVATION OF ANGULAR MOMENTUM Bike: faster spinning = more momentum, require external torque to change external momentum, falling over = complete loss of angular momentum in that plane, so large torque needed Kinetic chain: muscles continue adding torque, which increases angular acceleration and velocity and Vt. Radius increases, increasing Vt. As smaller limbs used, inertia decreases so angular velocity increases, increasing Vt. Hang: maximize moment of inertia to decrease rotation. Windmill: actively create moments due to limbs (high MoI, low w) and body rotates in opposite direction (low MoI, high w) and even though some torque created in wrong direction through legs, flex knee to decrease MoI Cat turning: top half rotates, bottom half has high MoI about that axis, so low w. Bottom half rotates, top half has high MoI.