Key Questions:
 What is torque?
 How do we calculate torque?
Performance Objectives
 Measure forces and distances in a
simple machine.
 Calculate torque.
 Apply the concept of mechanical
advantage to levers.
 Build three classes of levers.
Lever Assembly
 WATCH for FALLING weights on bare
toes or sandals or table tops!
 DO not place the fulcrum higher than
hole 3 of stand!
 Levers use torque to lift or move objects.
 Torque is a force applied over a distance that
causes ROTATION to occur.
 Torque is measured in Newtonmeters (Nm)
Review of levers
Input Force
x Length of
Input Arm
Output Force
x Length of
Output Arm
Force x Distance = Force x Distance
An Example of Torque
 Calculate the
torque created
when opening
the door.
1. Set up the balanced lever
2. Measure Forces and
3. Calculate input/output torques
Calibrate the spring scale
Torque and direction
 If more than one torque acts on an object, the torques are
combined to determine the net torque.
 If the torques tend to make an object spin in the same
direction (clockwise or counterclockwise), they are added
 If the torques tend to make the object spin in opposite
directions, the torques are subtracted.
 Torques causing counterclockwise rotation are positive
and torques causing clockwise rotation are negative.
Forces and Machines
 The variables in a simple machine
can be adjusted make work easier
or resist forces on purpose.
 Consider two levers:
Forces and Machines
 The advantage the simple machine gives to
the user can be calculated.
 A machine approaches a mechanical
advantage of 1, when output forces roughly
equal input forces.
Mechanical Advantage
Input force (N)
MA = Fo
Output force (N)
Mechanical advantage
 What is the mechanical advantage of
this new lever?
Torque and mechanical advantage
 What’s the mathematical relationship
between torque and mechanical
 MA = Output Torque ÷ Input Torque
Build different levers…
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
Levers and the human body
 Your body contains
muscles attached to
bones in ways that act
as levers.
 Here the biceps
muscle attached in
front of the elbow
opposes the muscles
in the forearm.
Can you think of other muscle
levers in your body?
Mobiles are levers!
 GREAT STEM project!
 Use science
 Think scientifically
 Communicate technical ideas
 Teach all students
 Be science conscious NOT
science phobic
What questions do you
have about Torque or
Mechanical Advantage?