Foundations of Physical
Science
Workshop: The Lever
The Lever
CPO Science
Key Questions
 How does a lever work?
 What is the relationship between force
and distance in a simple machine?
 What factors balance a lever?
Overview
 Describe how a lever works
 Identify the relationship between force
& distance on a lever
 Apply the concept of mechanical
advantage to levers
Introducing… The
Lever
 Anatomy of the lever
 Fulcrum – point around which the lever
rotates
 Input Force – Force exerted ON the lever
 Output Force – Force exerted BY the lever
Three Classes of Levers
 First Class - fulcrum
between Input and output
 Second Class – output
between fulcrum and input
 Third Class – input
between fulcrum and
output
CPO Lever – First Class All The Way
 Here we have a first class lever
 The fulcrum is between the input and output
 Can you get two weights to balance?
A Lever in
Equilibrium
 Hang your weights like shown here
 Does the lever balance?
 What variables can be changed to balance a
lever
Variables Involved
in Levers
 Amount of Input Force
 Amount of Output Force
 Length of Input Arm
 Length of Output Arm
Levers Investigation
 Hang weights from
the lever and get it
to balance
 Try 4 trials and
record how many
weights to hang
and where you
hang them
Mathematical Rule for
Balancing the Lever
 What mathematical relationship can you
find that will balance the lever every
time?
 Put your rule in terms of Input and
Output and forces and distances
 What if there is more than one location
on either side of the Lever?
What is the
Relationship?
 Input Force x Length of Input Arm=
Output Force x Length of Output arm
 Force x Distance = Force x Distance
 # of Weights x Distance = # of Weights x
Distance
What if there are several
groups of weights?
 Sum of Input = Sum of Output
 (Force a x Distance a) + (Force b x
Distance b) = (Force c x Distance c)
+ (Force d x Distance d)
Mechanical Advantage
We use the same kind of relationship for all
simple machines to calculate Mechanical
Advantage
 Output Force/Input Force
 Length Input Arm/Length Output Arm