Jan. 19
Objectives:
• Know and articulate the difference between work and torque.
• Measure and calculate torque in a lever system.
• Provide description of summative project requirements (specifications)
Bell Ringer:
(1) If you lifted a 412g shoe a distance of 3.7 cm with 150 g, how far did the 150 g mass move?
(2) What are two requirements for an event to be "work?"
(3) Describe one thing you do which is not work.
Lesson:
Summative Project
1) Distribute guidelines for trebuchet summative project. Discuss project with students; outline your requirements. Emphasize "no elastic launchers!" (This took 30 minutes!)
Lever Sense
2) Discuss affect of moving fulcrum on "what happens to the lever." Conversely, show how to balance an unbalanced lever by moving masses without moving the fulcrum. This is to help students develop a "Lever Sense."
Torque intro
3) Review procedure for using a balance to measure the mass of a students shoe with the "work" equation. Remind students that the difficulty was (i) measuring center of mass for shoe while it was sitting on the meter stick and (ii) measuring the distance the weight and shoe travelled up or down.
4) Demonstrate how moving the shoe farther from fulcrum makes it act heavier; point out: (i) mass of shoe is same (ii) but force of shoe is greater.
5) Explain that as shoe is moved farther from the fulcrum it seems to apply "more" force to lever EVEN WHILE LEVER IS NOT MOVING!
6) This affect is torque. Torque is created by force (the shoe) and how far the shoe is from the fulcrum. This is different than work; work depends on how far shoe moves; torque depends on how far the shoe is from the fulcrum. w = fd and t = fd; however, in work situation distance is parallel to force applied; in torque situation, the distance is perpendicular to force applied.
7) Discuss examples in which torque changes (ex. cheater bar on lug nut wrench, longer pry bar, opening door by pushing on handle instead of close to hinge, etc.)
Torque Practice
8) Students weigh their shoe using "torque" calculation in class (instead of work); have students hang shoe an weight by string so that distance is clearer to measure to improve accuracy .
Assignment:
1) Complete "Lever Sense" handout [I also distributed "Torque" handout but did not have time to instruct or complete it.]
