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  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 Force x Distance = Force x Distance Input Force x Length of Input Arm Torque Output Force x Length of Output Arm = Force = Distance X

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.

Mechanical Advantage MA = F o F i Output force (N) Input force (N) mechanical advantage

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

What questions do you have about Torque or Mechanical Advantage?