4 FUNCTIONS of MACHINES 1. Balance 2 or more Forces 2. Force advantage 3. Linear ROM and/or Speed 4. Change direction of F motive

3 Components of Levers 1. Axis or fulcrum 2. Motive Force 3. Resistive Force

PROPERTIES OF A FORCE 1. Magnitude 2. Direction 3. Point of Application 4. Line of Action

No Torque Net Torque No FA example Fig 4.3d No FA example Fig 4.3d Imbalance of Tm & Tr resultant motion in the direction of the greatest Torque T motive = T resistive T motive = T resistive

FA resistive action line of gravity acting through lower arm’s c of g to axis of rotation (elbow joint) FA motive action line of muscle pulling on bone to axis of rotation (elbow joint)

Figure 4.4 on page 149  4.4a T motive = T resistive  result is no motion  4.4b T motive > T resistive  resultant motion is ccw  4.4c T motive < T resistive  resultant motion is cw

Figure Question 2 page 151 if A = 100 weight units d must = 1.0 distance units if A = 100 weight units d must = 1.0 distance units if A = 40 weight units d must = 2.5 distance units if A = 40 weight units d must = 2.5 distance units

Resultant Torque Vector  Resultant Arrow represents Magnitude & Direction  Resultant comprised of 2 components: 1. Ro = vertical/perpendicular component 2. Stabl or Disl = horizontal/parallel component

Position 1 more Stabl than Ro Position 2 100% Ro Position 3 more Disl than Ro Figure 4.8 on page 154

Figure 4.10 on page 156  F 1 = Stabl (pulls toward axis/joint)  FA for F 1 =  d from axis to F 1  F 2 = 100% Ro (no horz component)  FA for F 2 =  d from axis to F 2  F 3 = Disl (pulls away from axis/joint)  FA for F 3 =  d from axis to F 3

Figure 4.12b on page Draw Resultant Motive Force Vector 2. Draw Resultant Resistive Force Vector 3. Draw Motive and Resistive FA’s

FIG 4.12b page 157

Mechanical Disadvantage Advantage FA MOTIVE < FA RESISTIVE FA MOTIVE < FA RESISTIVE LARGER F MOTIVE required to overcome SMALLER F RESISTIVE LARGER F MOTIVE required to overcome SMALLER F RESISTIVE 3rd class levers 3rd class levers FA MOTIVE > FA RESISTIVE SMALLER F MOTIVE required to overcome LARGER F RESISTIVE 1 st and 2 nd class levers

 Axis/Fulcrum between MF and RF  rare in human body  serves all 4 functions of machines 1 st Class Lever Fig “Basic Biomechanics” Susan J. Hall 3 rd edition

 Axis at one end, F motive further away than F resisitive  FA motive > FA resisitive  only serves 1 function of machines 2 nd Class Lever Fig “Basic Biomechanics” Susan J. Hall 3 rd edition

 Axis at one end, F resisitive further away than F motive  FA motive < FA resisitive  only serves 1 function of machines 3 rd Class Lever Fig “Basic Biomechanics” Susan J. Hall 3 rd edition

Wheel and Axle  A machine that gives either a Force advantage OR a ROM advantage  F advantage = F motive applied to wheel  ROM advantage = F motive applied to axel  in humans most common = ROM advantage

Wheel and Axle