4 FUNCTIONS of MACHINES

1.1. Balance 2 or more ForcesBalance 2 or more Forces

2.2. Force advantage Force advantage

3.3. Linear ROM and/or SpeedLinear ROM and/or Speed

4.4. Change direction of F motiveChange direction of F motive

3 Components of Levers

1.1. Axis or fulcrum Axis or fulcrum

2.2. Motive ForceMotive Force

3.3. Resistive ForceResistive Force

PROPERTIES OF A FORCE

1.1. MagnitudeMagnitude

2.2. DirectionDirection

3.3. Point of ApplicationPoint of Application

4.4. Line of ActionLine of Action

No Torque Net Torque

No FANo FAexample Fig 4.3d example Fig 4.3d

Imbalance of Tm & TrImbalance of Tm & Tr

resultant motion in resultant motion in the direction of the the direction of the greatest Torquegreatest Torque

T motive = T resistiveT motive = T resistive

FA resistiveFA resistiveaction line ofaction line of gravitygravity acting through lower acting through lower arm’s c of g to axis of arm’s c of g to axis of rotation (elbow joint)rotation (elbow joint)

FA motiveFA motiveaction line ofaction line of musclemuscle pulling on bone to axis pulling on bone to axis of rotation (elbow joint)of rotation (elbow joint)

Figure 4.4 on page 149 4.4a T4.4a Tmotivemotive = T = Tresistiveresistive result is no motionresult is no motion

4.4b T4.4b Tmotivemotive > T > Tresistiveresistive resultant motion is ccw resultant motion is ccw

4.4c T4.4c Tmotivemotive < T < Tresistiveresistive resultant motion is cwresultant motion is cw

Figure 4.6 - Question 2 page 151

if A = 100 weight unitsif A = 100 weight units

d must = 1.0 distance unitsd must = 1.0 distance units

if A = 40 weight unitsif A = 40 weight units

d must = 2.5 distance unitsd must = 2.5 distance units

Resultant Torque Vector Resultant Arrow represents Magnitude & DirectionResultant Arrow represents Magnitude & Direction

Resultant comprised of 2 components:Resultant comprised of 2 components:

1. 1. RoRo = vertical/perpendicular component = vertical/perpendicular component

2. 2. StablStabl or or DislDisl = horizontal/parallel component = horizontal/parallel component

Position 1Position 1moremore StablStabl than Rothan Ro

Position 2Position 2100% 100% RoRo

Position 3Position 3moremore DislDisl than Rothan Ro

Figure 4.8 on page 154

Figure 4.10 on page 156 FF11 = Stabl (pulls toward axis/joint) = Stabl (pulls toward axis/joint)

FA for FFA for F11 = = d from axis to F d from axis to F11

FF22 = 100% Ro (no horz component) = 100% Ro (no horz component)

FA for FFA for F22 = = d from axis to F d from axis to F22

FF33 = Disl (pulls away from axis/joint) = Disl (pulls away from axis/joint)

FA for FFA for F33 = = d from axis to F d from axis to F33

Figure 4.12b on page 157

1.1. Draw Resultant Motive Force VectorDraw Resultant Motive Force Vector

2.2. Draw Resultant Resistive Force VectorDraw Resultant Resistive Force Vector

3.3. Draw Motive and Resistive FA’sDraw Motive and Resistive FA’s

FIG 4.12b

page 157

MechanicalDisadvantage Advantage

FAFAMOTIVEMOTIVE < < FAFA RESISTIVERESISTIVE

LARGERLARGER FFMOTIVEMOTIVE

requiredrequired to overcome to overcome

SMALLERSMALLER FFRESISTIVERESISTIVE

3rd class levers3rd class levers

FAFAMOTIVEMOTIVE > > FA FARESISTIVERESISTIVE

SMALLERSMALLER FFMOTIVE MOTIVE required to overcome required to overcome LARGER LARGER FFRESISTIVERESISTIVE

11stst and 2 and 2ndnd class levers class levers

Axis/Fulcrum between MF and RFAxis/Fulcrum between MF and RFrare in human bodyrare in human bodyserves all 4 functions of machinesserves all 4 functions of machines

1st Class Lever

Fig 13.11 “Basic Biomechanics” Susan J. Hall 3rd edition

Axis at one end, FAxis at one end, Fmotivemotive further away than Ffurther away than Fresisitiveresisitive

FAFAmotivemotive > FA > FAresisitiveresisitive

only serves 1 function of machinesonly serves 1 function of machines

2nd Class Lever

Fig 13.11 “Basic Biomechanics” Susan J. Hall 3rd edition

Axis at one end, FAxis at one end, Fresisitiveresisitive further away than F further away than Fmotivemotive

FAFAmotivemotive < FA < FAresisitiveresisitive

only serves 1 function of machinesonly serves 1 function of machines

3rd Class Lever

Fig 13.11 “Basic Biomechanics” Susan J. Hall 3rd edition

Wheel and Axle A machine that gives either a Force A machine that gives either a Force

advantage OR a ROM advantageadvantage OR a ROM advantage

F advantage = FF advantage = Fmotivemotive applied to applied to wheelwheel

ROM advantage = FROM advantage = Fmotivemotive applied to applied to axelaxel

in humans most common = ROM in humans most common = ROM advantageadvantage

Wheel and Axle