 What is torque?
 How do we calculate torque?

 Measure forces and distances in a simple machine.
 Calculate torque.
 Apply the concept of mechanical advantage to levers.
 Build three classes of levers.

 SAFETY NOTE:
 WATCH for FALLING weights on bare toes or sandals or table tops!
 DO not place the fulcrum higher than hole 3 of stand!

Torque
 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
Torque
=
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

Data

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 together.
 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.

Output force (N) mechanical advantage
MA = F o
F i
Input 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 advantage?
 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!

Outcomes
 Use science
 Think scientifically
 Communicate technical ideas
 Teach all students
 Be science conscious NOT science phobic