1. Levers

2. What is a Lever?! In Our Body
A lever is a rigid bar that rotates around an axis (fulcrum).
In Our Body
Bones  act as the rigid bar
Joints  act as the axis (fulcrum)
Muscle  apply the force

3. A Lever Consists of Three Components
Resistance Force Arm: the perpendicular distance from the line of action of the resistance to the fulcrum.
Effort Force Arm: the perpendicular distance from the line of action of the effort force to the fulcrum.
Fulcrum: the axis which a lever may rotate around

4. Classes of Levers First Class Lever Second Class Lever
Third Class Lever

5. First Class Lever Mechanical Examples
The fulcrum is between the effort force & the resistance force.
The effort force & the resistance can be at an equal distance from the fulcrum, or one may be farther away than the other
Mechanical Examples
Scissor
teeter-totter

6. Anatomical Example Extension of the head
Fulcrum: Atlanto-occipital joint
Resistance: weight of the head
Effort force: neck extensors

7. Second Class Lever Mechanical Examples
The resistance is between the effort force & the fulcrum.
The effort force & the resistance are on the same side of the axis, with the resistance closer to the fulcrum
Mechanical Examples
Wheel-barrow
Nutcracker

8. Rising of heals to stand on toes
Anatomical Example
Rising of heals to stand on toes
Fulcrum: metatarsophalangeal joints
Resistance: weight of the body
Effort force: Planterflexors (Calf muscles)

9. Third Class Lever Mechanical Examples
The effort force is between the resistance & the fulcrum.
The effort force acts between the fulcrum & the line of resistance force
Mechanical Examples
Fishing poles Shoveling
Tweezers

10. Anatomical Example Forearm Flexion Fulcrum: Elbow joint
Resistance: object held in hand
Effort force: biceps muscle

11. What is Mechanical Advantage?!
Mechanical advantage is the ratio of force arm to resistance arm of a giver lever.
MA = effort force arm / resistance force arm

12. What If Mechanical Advantage = 1
Effort force arm = resistance force arm
There will be a change in the direction of movement only

13. What If Mechanical Advantage > 1
Effort force is smaller than resistance force
 distance effort force moves, meaning that the distance moved by the effort is greater than the distance moved by the resistance

14. What If Mechanical Advantage < 1
Effort force in more than resistance force
 distance effort force moves, meaning that the distance moved by the effort is lesser than the distance moved by the resistance

15. In First Class Lever Mechanical advantage can be: = 1 < 1 > 1
Can be used to gain force advantage or distance/speed advantage

16. In Second Class Lever In Third Class Lever
Mechanical advantage can be is ALWAYS > 1
Used to gain force advantage
In Third Class Lever
Mechanical advantage can be is ALWAYS < 1
Most human levers are class III

17.  Study Hard & Good Luck 