Foundations of Physical Science

Workshop: The Lever

The LeverCPO 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