The document discusses levers in the human body. It defines levers as rigid bars that rotate around a fulcrum or axis. There are three classes of levers - first class has the fulcrum between the effort and resistance arms, second class has the resistance arm between the effort and fulcrum, and third class has the effort arm between the fulcrum and resistance. Examples of each class in the human body include the head lifting muscles using the atlas joint as a first class lever, the Achilles tendon acting as a second class lever, and the bicep muscle bending the elbow as a third class lever. Levers in the body allow for increased power, distance, speed, and precision of

1. Regents Biology 2015/2016
[ Levers in human
body ]
Mohamed M.Elsaied
2016/2017
Supervised by :- Dr. Abouzeid A.Thabet
Allied Medical Science
Biomechanics

2.  Introduction
Mohamed M.Elsaied
2016/2017
 When person is moving his leg - arms -
any part of his body
He depend on his Skelton system
(muscle forces)
by contraction or extension muscles.
 In fact the bone in moving work as
A lever
 Levers cannot be changed, but they
can be utilized more efficiently .

3.  levers
Mohamed M.Elsaied
2016/2017
 Definition of levers
A rigid bar that turns about an axis of rotation or a fulcrum .
 Parts of a lever
- Fulcrum Axis of rotation of the lever .
- Effort Arm The part of the lever that the effort force .
- Resistance Arm The part of the lever
that applies the resistance force .

4.  Classification of levers
Mohamed M.Elsaied
2016/2017
 First Class Lever
A first-class lever is a lever in which the fulcrum (Axis) is located
between the input effort (Force) and the output load (Resistance).
 Second Class Lever
Resistance (load) is located between the effort arm and the
fulcrum .
 Third Class Lever
The effort force is located between the fulcrum and the resistance .

5.  The 3 Classes of Levers
Mohamed M.Elsaied
2016/2017
| Resistance Arm |
| Force Arm |
A
F R
| Force Arm | | Resistance Arm |
A
R| Resistance Arm | F
A
R
| Force Arm |
F
• FAR
1st
• ARF
2nd
• AFR
3rd

6.  1 st class of lever in human body
Mohamed M.Elsaied
2016/2017
 The joint between the skull and the atlas vertebrae of the spine
the spine is the fulcrum across which muscles lift the head .

7. Mohamed M.Elsaied
2016/2017
 The joint between the hummers and radius – ulna .

8.  2 nd class of lever in human body
Mohamed M.Elsaied
2016/2017
 The Achilles tendon, pushing or pulling across the heel of the foot .

9. Mohamed M.Elsaied
2016/2017

10.  3 rd class of lever in human body
Mohamed M.Elsaied
2016/2017
 The elbow joint: when lifting a book, the elbow joint is the fulcrum
across which the biceps muscle performs the work.

11. Mohamed M.Elsaied
2016/2017

12.  Benefit from lever ?
Mohamed M.Elsaied
2016/2017
 Increase power
 Increase distance
 Increase speed
 Transfer power from one place to another
 precision in work safety
 Avoid risks

13.  Reference
Mohamed M.Elsaied
2016/2017
www.dynamicscience.com.au/tester/solutions/hydraulicus/simplemach
ineslevers1.htm
http://www.montgomery.k12.ky.us/camargo/Projects/simplemachines/
simplemachines.htm

http://www.dynamicscience.com.au/tester/solutions/hydraulicus/human
body.htm