Download 13-4 Levers in the Body 2013

• Levers in the Body
PH 532
EQ: How does your body work as
a machine?
1. What is a force?
• A push or pull on an object.
• Force is represented by
arrows
• The units of force are:
Newton (N)
2. What is work?
• When a force makes an object move
• Why does it take more work to lift a
heavier plant?
Because a greater force is required!
3. What is a machine?
• Devices that help you do work
4. What is a lever?
• A rigid object that rotates about a fixed point
(fulcrum)
A) A simple machine…helps you do work!
Fulcrum: a fixed point …where a lever rotates
Diagram:
5. How does a lever make work easier?
1. Changing the amount of force,
2. Changing the distance,
3. Changing the direction.
• Why does the girl place the
fulcrum close to the crate?
To increase the force as much as
possible!
6. What is mechanical advantage?
• A measure of how much easier it is to do
work by using a machine
7. How do you find the mechanical
advantage of a lever?
Mechanical advantage = resistance force
effort force
100 N
25 N
• Or:
Length of Effort Arm
Length of Resistance Arm
8. What are the 3 kinds of
levers?
• 1. First Class
• 2. Second Class
• 3. Third Class
9. Draw a first class lever.
1st class
Example: see-saw, scissors, crowbar
Body: neck!
2nd class
Examples: wheelbarrow
Body: foot!
3rd class
Example: broom, rake, catapult
Body: arm
• How many different classes of
levers are there?
Three!
9. How do levers function on the
body?
• Bones and muscles work as lever systems
joint = fulcrum
bone = lever
muscles = provide force