2. Key Questions:  What is torque?  How do we calculate torque?

3. 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.

4. 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!

5. 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)

6. 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

7. An Example of Torque  Calculate the torque created when opening the door.

8. 1. Set up the balanced lever

9. 2. Measure Forces and 3. Calculate input/output torques

10. Calibrate the spring scale

11. Data

12. 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.

13. Forces and Machines  The variables in a simple machine can be adjusted make work easier or resist forces on purpose.  Consider two levers:

14. 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.

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

16. Mechanical advantage  What is the mechanical advantage of this new lever?

17. Torque and mechanical advantage  What’s the mathematical relationship between torque and mechanical advantage?  MA = Output Torque ÷ Input Torque

18. Build different levers…

19. 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

20. 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?

21. Mobiles are levers!  GREAT STEM project!

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

23. What questions do you have about Torque or Mechanical Advantage?