Levers

1
Levers

• Muscles bones joints lever system
• A level is a rigid structure that moves a fulcrum
  (fixed point)
• 3 important components to levers
• Load (resistance)
• Fulcrum
• Effort (applied force)

2

• Levers allow a given effort (muscle tension) to
  move a heaver load, or move a load farther of
  faster than otherwise would.

3

• Mechanical advantage
• Small effort over a large distance.
• Load is closer to fulcrum than effort.
• Less effort moves a large load a small distance.
• Mechanical disadvantage
• Effort is larger than load.
• Effort is closer to fulcrum.
• Effort allows load to move rapidly over a large
  distance
• ? Trade-off (effort vs. movement)

4
Classes of levers

• First class
• Fulcrum located between the load and lever
• Few found in human body

5
Classes of levers

• Second class
• Load if found between the effort and fulcrum
• Small force can move a large weight
• Few found in the human body.

6
Classes of levers

• Third class
• Force applied between the load and the fulcrum
• Load is moved quickly and farther at expense of
  effort
• Always at a mechanical disadvantage
• Most common lever in human body.

7
Classes of levers

• Third class, continued
• Muscles insert close to fulcrum, allowing rapid
  and extensive movement
• Relatively little muscle shortening

8

• A lever moves when applied force is large enough
  to overcome resistance
• Length of the level on each side of the fulcrum
  affects the force needed to overcome resistance.

9
Torque

• Levers are composed of two arms
• Input Lever
• Output Lever
• Torque Force Lever Arm (Nm)

10
Torque

• Input torque and output torque are always equal
  (frictionless fulcrum)
• With a given input force, the output force will
  be a function of the relative arm lengths (lever
  arm ratioLAR)
• LAR gt 1 ? mechanical advantage (less input force
  with greater output force)
• LAR gt 1 ? mechanical disadvantage