WHY does C work best?

3. Suppose you try to prop open the door below with a lab stool 3 times. First, you put a stool by the HINGE (see then ‘x’). Then, you put a stool in the middle. Finally, you put a stool by the handle. WHICH IS MOST EFFECTIVE?

4. WHY does C work best? • Same door • Same stool • Same force… • What’s different?

5. Suppose you try to push open the door below 3 times. First, you push by the HINGE (see then ‘x’). Then, you push in the middle. Finally, you push by the handle. WHICH IS EASIEST?

6. If you cannot exert enough torque to turn a stubborn bolt, would more torque be produced if you fastened a length of rope to the wrench handle as shown? • YES • NO • IMPOSSIBLE TO SAY

7. On to the POGIL! • We are completing some of this together as a class, and some on your own.

8. Discuss and complete with the people around you

9. Try #2-6!

10. 2. Look the formula above for TORQUE. Which of the following produces the greatest torque? • Small force, short lever arm • Large force, small lever arm • Small force, long lever arm • Large force, long lever arm.

11. 3. Torque is (directly, inversely) proportional to the perpendicular force. • Directly • inversely

12. 4. Torque is (directly, inversely) proportional to the lever arm. • Directly • inversely

13. 5. COMPLETE THE SENTENCE: The same torque can be produced by a large force with a short lever arm, or a small force with a ____. • short lever arm • long lever arm • Neither

14. F x LA = Torque = F x LA

15. Fx LA = Torque = F x LA You can get the SAME TORQUE (door opens) by pushing with diff. forces! 1 3 1 1 3 3

16. Try #8-10 Check in at STOPSIGN.Then, do #11.Check in your TEXT.Finally, do #12.You have 5 minutes

17. What is different from scenario 1 to scenario 2? Which has more torque and why? • 1 because the hand is angled • 1 because more force • 1 because smaller lever arm • 1 because larger lever arm • 2 because the hand is perpendicular • 2 because more force • 2 because smaller lever arm • 2 because larger lever arm • Same torque • Not sure/ not enough info Countdown

18. What is different from scenario 2 to scenario 3? Which has more torque and why? • 3 because the hand is angled • 3 because more force • 3 because smaller lever arm • 3 because larger lever arm • 2 because the hand is perpendicular • 2 because more force • 2 because smaller lever arm • 2 because larger lever arm • Same torque • Not sure/ not enough info Countdown

19. 9. Can the same force produce different amounts of torque? • Yes • No • Not sure/not enough info If you apply the same force to different lever arms, you can get different torques! Or, if you apply the same force, but apply it at an angle vs. perpendicular!

20. 10. Can the same torque be exerted from different forces? • Yes • No • Not sure/not enough info If you apply different forces to different lever arms, you can get the same torque! F x LA = Torque = F x LA You can get the SAME TORQUE by pushing with diff. forces!

21. 11. If you cannot exert enough torque to turn a stubborn bolt, would more torque be produced if you fastened a length of rope to the wrench handle as shown? • YES • NO • IMPOSSIBLE TO SAY The rope doesn’t change the lever arm! You need a stronger person (more force), or a bigger wrench (bigger lever arm)! SEE PAGE 152 YELLOW BOX

22. 12. When the CG is not over the area of support, what force produces a torque that causes toppling? • Perpendicular force • Gravity • Support force • Not sure/ not enough info

23. 11.2Balanced Torques A pair of torques can balance each other. Balance is achieved if the torque that tends to produce clockwise rotation by the boy equals the torque that tends to produce counterclockwise rotation by the girl.

24. Torque Formulas • Weight alone does not produce rotation—torque does. • When balanced torques act on an object, there is no change in rotation. • 2 kids can balance a see-saw even when their weights are not equal! • A pair of torques can balance each other. • Balance is achieved if the torque that tends to produce clockwise rotation (by the boy) equals the torque that tends to produce counterclockwise rotation (by the girl.) Torque counterclockwise = Torque clockwise (Force x Lever Arm)counterclockwise = (Force x Lever Arm )clockwise

25. Calculations: • Calculate the girl’s torque: • What is the girl’s weight? (this is the Perpendicular Force) • What is the girl’s DISTANCE from the FULCRUM/TURNING POINT? (This is the Lever Arm) • Calculate the girl’s torque: *Show all work; the unit for torque is the Newton Meter ( Nm) 2. Calculate the boy’s torque: • What is the boy’s weight? (this is the Perpendicular Force) • What is the boy’s DISTANCE from the FULCRUM/TURNING POINT? (This is the Lever Arm) • Calculate the boy’s torque: *Show all work; the unit for torque is the Newton Meter ( Nm) 400 N 200 N 1.5 m 3 m F x LA = τ 400 N x 1.5m = 600 Nm F x LA = τ 200 N x 3m = 600 Nm

26. 11.2Balanced Torques do the math! The block of unknown weight tends to rotate the system of blocks and stick counterclockwise, and the 20-N block tends to rotate the system clockwise. The system is in balance when the two torques are equal: counterclockwise torque = clockwise torque

27. 11.2Balanced Torques do the math! What is the weight of the block hung at the 10-cm mark? CAREFUL with your LEVER ARMS!!!

28. 11.2Balanced Torques First, let’s check…which object has a larger lever arm? So…which force has to be larger? F x LA= τ = F x LA So we know our ‘mystery weight’ is less than 20 N F x LA = τ = F x LA F x 40 cm= τ = 20 Nx 30 cm F x 40 cm = 600 N cm Divide both sides by 40 cm …. Force = 15 N

29. Webquest! • Follow all directions • Check in when you need clarification or assistance • EVERY STUDENT WILL COMPLETE A WEBQUEST to KEEP (the handout you just received) • Must be finished TODAY • Anything you do not finish will be HW • You need to finish #1-9…#10 is a challenge • (trial & error – try it  But if you struggle, don’t stress) • Not collecting this…because EVERY STUDENT will then use the solutions from the Web Quest to complete an INDIVIDUAL GRADED POST LAB at the start of next class! (open notes) • Stopping with 2 minutes left for a clicker exit

30. The broom balances at its CG. If you cut the broom at its CG and weighed each side, which side would weigh more? • The broom HANDLE side • The broom BRUSH SIDE • They weigh the same • Not sure/not enough info F x LA = Torque = F x LA