Biomechanics Exam 2

Question 1

What do force plates do?

Answer 1

Measure three orthogonal reaction forces, Fx, Fy, Fz and three moments about these orthogonal axes, Mx, My, and Mz.

Question 2

How do force plates measure force?

Answer 2

Through transducers sandwiched between rigid plates that convert force into voltage.

Question 3

Ground Force Reaction

Answer 3

The reaction force provided by the support surface on which the movement is performed.

Question 4

Calculate the resultant of the 3 reaction force vectors

Answer 4

Square root of the sum of the component forces squared

Question 5

GRF Angles

Answer 5

Theta yz = inversetan(Fy/Fz)
Theta xz = inversetan(Fx/Fz)
Theta xy = inversetan(Fx/Fy)

Question 6

Center of Pressure

Answer 6

Point on the force plate that the resultant force originates

Question 7

COP(x)

Answer 7

My/Fz

Question 8

COP(y)

Answer 8

Mx/Fz

Question 9

Newton’s 1st Law

Answer 9

A body continues in its state of rest or uniform motion in a straight line unless compelled to change the state by external forces exerted upon it. Due to mass or inertia.

Question 10

Inertia

Answer 10

property of a body to resist a change in its state of motion.

Question 11

Moment of Inertia

Answer 11

Sum of m*r^2

Question 12

Angular Momentum

Answer 12

Moment of inertia * Angular velocity

Question 13

Newton’s 2nd Law

Answer 13

An unbalanced force applied to a body causes acceleration of that body (sum of the forces equals mass times acceleration)

Question 14

Newton’s 2nd Law - Angular Acceleration

Answer 14

Sum of the torque equals Inertia time angular acceleration

Question 15

Torque

Answer 15

Radius cross the force

Question 16

Newton’s 3rd Law

Answer 16

For every action there is an equal and opposite reaction (torque and/or force)
Forces always come in pairs

Question 17

Momentum

Answer 17

mass times velocity

Question 18

Elastic collisions

Answer 18

objects rebound

Question 19

Inelastic collisions

Answer 19

object stick together and usually become distorted and generate heat.

Question 20

Coefficient of Restitution

Answer 20

describes the relative elasticity of an impact
perfectly elastic e = 1
inelastic e = 0
e = velocity after / velocity before

Question 21

Kinetic Energy

Answer 21

(1/2) m*v^2

Question 22

Power

Answer 22

Force * velocity

Question 23

1 hp

Answer 23

550 ft lbs / s = 746 W

Question 24

Potential Energy

Answer 24

mgh

Question 25

Motor Units

Answer 25

motor neuron and muscle fibers it innervates

Question 26

Fine control

Answer 26

small motor units contain as few as 20 muscle fibers per nerve fiber

Question 27

Strength control

Answer 27

a large number of muscle fibers per nerve fiber

Question 28

Erector Spiane Muscle

Answer 28

extends down the back, responsible for maintaining back posture in any "sitting" position.

Question 29

Basic strategies to prevent overexertion injury?

Answer 29

Design, select, train

Question 30

Recommended Weight Limit | (RWL) Equation

Answer 30

LC*HM*VM*DM*AM*FM*CM

Question 31

Lift Index (LI)

Answer 31

Task Load / RWL

Question 32

What does Lift Index (LI) mean?

Answer 32

LI < 1 - lifting task is safe for most workers | LI > 3 - many workers are at elevated risk

Question 33

Load Constant (LC)

Answer 33

max recommended weight for lifting at standard 23 kg or 51 lbs

Question 34

Horizontal Multiplier (HM)

Answer 34

HM (metric) = 25/H HM (english) = 10/H H = horizontal distance from hands to midpoint

Question 35

Velocity Multiplier (VM)

Answer 35

VM = (1-0.003 (V-75)) (cm) VM = (1-0.0075 (V-30)) (in) V is vertical distance of hands from floor

Question 36

Distance Multiplier (DM)

Answer 36

D is total vertical distance moved between origin and destination

Question 37

Asymmetric Multiplier (AM)

Answer 37

A is angle of symmetry (angular displacement in sagittal plane)

Question 38

Frequency Multiplier (FM)

Answer 38

based on work duration and V (vertical distance from floor)

Question 39

Coupling Multiplier (CM)

Answer 39

based on V (vertical distance of hands from floor in cm) and quality of coupling

Question 40

Area under a force distance curve is ____ .

Answer 40

Work

Question 41

Units associated with impulse are ____ .

Answer 41

Newtons * sec

Question 42

Torque is angular acceleration * ____ .

Answer 42

Inertia

Question 43

Angular velocity * Inertia

Answer 43

Angular Momentum

Question 44

Which multiplier in the NIOSH lifting equation has the most influence on determining the safety of a given task?

Answer 44

HM (Horizontal Multiplier)