Biomechanics

1
Biomechanics

• Biomechanics breaks the body down into a number
  of simple machines.
• Each machine contains
• A fulcrum
• 2 lever arms
• A force put into the machine
• A force gotten out of the machine

2
Torques

• When a force is applied to a lever system, Force
  x Lever Length Torque
• Force(in) x Lever Length(in) Torque(in)
• Force(out) x Lever Length(out) Torque(out)
• Both Torques must be equal in a system
• F(i) x L(i) F(o) x L(o)

3
Type I Lever System
4
Type II Lever System
5
Type III Lever System
6
Example Using Type I System

• Assume that the triceps muscle exerts an in force
  of 10 Newtons, the length of the in lever
  100mm, and the length of the out lever 250mm
• Force(out) x 250mm 10 Newtons x 100mm
• 250F(out) 1000 F(out) 4 Newtons

7
Can Also Calculate

• Mechanical Advantage
• Force(out)/Force(in) Mechanical Advantage
• MA F(o)/F(i)
• Velocity Ratio
• Velocity(out)/Velocity(in) Velocity Ratio
• VR 1/MA

8
What to do if You Dont Know F(i)

• F(i) x L(i) F(o) x L(o)
• Rearrange the equation as
• F(o) / F(i) L(i) / L(o)
• MA L(i) / L(o)
• VR L(o) / L(i)

9
Use A Skeleton

• Type I Lever System
• Mole has L(i) 7mm and L(o) 15mm
• Opossum has L(i) 14mm and L(o) 81mm
• Giraffe has L(i) 75mm and L(o) 1490mm
• Assume F(i) 10 Newtons, Calculate F(o), MA, and
  VR