1. 4.2 The Lever
How does a lever work?

2. Key Points Lever How does it work? Classes or types
Mechanical advantage

3. Lever Made of: Lever Stiff structure that rotates around a fixed point
Fulcrum
Fixed point a lever rotates around
Input arm
Side of the lever where the input force is applied
Output arm
Side of the lever that moves or lifts something

4. Mechanical Advantage Two ways: Same formula as block and tackle
MA = Li / Lo
Li = Length of input arm
Lo = Length of output arm

5. Mechanical Advantage for a Lever
Formula
If you know…
And you need…
MA = Li / Lo
Length of input and output arms
Mechanical advantage
Li = MA * Lo
Mechanical advantage and length of output arm
Length of input arm
Lo = Li / MA
Length of input arm and mechanical advantage
Length of output arm

6. First Class Fulcrum is between the input and output arms Examples:
Spine attaches to head
Vice grips
Input
Output
Fulcrum

7. Second Class Output force is between the input force and the fulcrum
Examples:
Wheelbarrow
Standing on tiptoes
Output
Input
Fulcrum

8. Third Class Input force is between the output force and the fulcrum
No mechanical advantage
Greater speed and range of movement
Example:
Biceps
Input
Output
Fulcrum