4 FUNCTIONS of MACHINES

1
4 FUNCTIONS of MACHINES

• Balance 2 or more Forces
• Force advantage
• Linear ROM and/or Speed
• Change direction of F motive

2
3 Components of Levers

• Axis or fulcrum
• Motive Force
• Resistive Force

3
PROPERTIES OF A FORCE

• Magnitude
• Direction
• Point of Application
• Line of Action

4
No Torque Net Torque

• Imbalance of Tm Tr
• resultant motion in the direction of the greatest
  Torque

• No FAexample Fig 4.3d

• T motive T resistive

5
FA resistiveaction line of gravity acting
through lower arms c of g to axis of rotation
(elbow joint)FA motiveaction line of muscle
pulling on bone to axis of rotation (elbow joint)
6
Figure 4.4 on page 149

• 4.4a Tmotive Tresistive ? result is no motion
• 4.4b Tmotive gt Tresistive ? resultant motion
  is ccw
• 4.4c Tmotive lt Tresistive ? resultant motion is
  cw

7
Figure 4.6 - Question 2 page 151

• if A 100 weight unitsd must 1.0 distance
  units
• if A 40 weight unitsd must 2.5 distance
  units

8
Resultant Torque Vector

• Resultant Arrow represents Magnitude Direction
• Resultant comprised of 2 components1. Ro
  vertical/perpendicular component2. Stabl or
  Disl horizontal/parallel component

9

• Position 1more Stabl than RoPosition 2100
  RoPosition 3more Disl than Ro

Figure 4.8 on page 154
10
Figure 4.10 on page 156

• F1 Stabl (pulls toward axis/joint)
• FA for F1 ? d from axis to F1
• F2 100 Ro (no horz component)
• FA for F2 ? d from axis to F2
• F3 Disl (pulls away from axis/joint)
• FA for F3 ? d from axis to F3

11
Figure 4.12b on page 157

• Draw Resultant Motive Force Vector
• Draw Resultant Resistive Force Vector
• Draw Motive and Resistive FAs

12
FIG 4.12b page 157
13
MechanicalDisadvantage
Advantage

• FAMOTIVE gt FARESISTIVE
• SMALLER FMOTIVE required to overcome LARGER
  FRESISTIVE
• 1st and 2nd class levers

• FAMOTIVE lt FA RESISTIVE
• LARGER FMOTIVE required to overcome SMALLER
  FRESISTIVE
• 3rd class levers

14
1st Class Lever

• Axis/Fulcrum between MF and RF
• rare in human body
• serves all 4 functions of machines

Fig 13.11 Basic Biomechanics Susan J. Hall
3rd edition
15
2nd Class Lever

• Axis at one end, Fmotive further away than
  Fresisitive
• FAmotive gt FAresisitive
• only serves 1 function of machines

Fig 13.11 Basic Biomechanics Susan J. Hall
3rd edition
16
3rd Class Lever

• Axis at one end, Fresisitive further away than
  Fmotive
• FAmotive lt FAresisitive
• only serves 1 function of machines

Fig 13.11 Basic Biomechanics Susan J. Hall
3rd edition
17
Wheel and Axle

• A machine that gives either a Force advantage OR
  a ROM advantage
• F advantage Fmotive applied to wheel
• ROM advantage Fmotive applied to axel
• in humans most common ROM advantage

18
Wheel and Axle