HW Due Read & Study Ch 11; Ch 11 vocab

Tonight’s HW

• Read & Study 11.1 - 11.3 • Do #1-6, 21 – 24, 26, 33 (p. 165–66) (13 pts – 1 pt each and 1 pt for 1 graded on correctness)

• TEST on Ch 10 & 11 on May 7(A) & May 8(B)• Print out & Finish the study guide by END of

class May 5(A) & 6(B) for +5 on your test

Do Now Grab a clicker – set asideTake back your CH 9 & 12 test – MAKE CORRECTIONS! Need help? Ask a teacher or peer. YOUR FINAL EXAM is in 7 weeks and you WILL see these questions on there!

HW Due Read & Study Ch 11; Ch 11 vocab

Tonight’s HW

• Read & Study 11.1 - 11.3 • Do #1-6, 21 – 24, 26, 33 (p. 165–66) (13 pts – 1 pt each and 1 pt for 1 graded on correctness)

• TEST on Ch 10 & 11 on May 8(B)• Print out & Finish the study guide by END of

class on May 6(B) for +5 on your test

Do Now Grab a clicker – set asideTurn in your HWHave a seat

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?

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0% A. B. C.

WHY does C work best?

• Same door• Same stool• Same force…

• What’s different?

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? 

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0% A. B. C.

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?

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0% A. YESB. NOC. IMPOSSIBLE TO SAY

On to the POGIL!• We are completing some of this together as a

class, and some on your own.

• Discuss and complete with the people around you

Try #2-6!

2. Look the formula above for TORQUE. Which of the following produces the greatest torque?

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0% A. Small force, short lever armB. Large force, small lever armC. Small force, long lever armD. Large force, long lever arm.

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

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B. inversely

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

0%0% A. Directly

B. inversely

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 ____.

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0% A. short lever armB. long lever armC. Neither

F x LA = Torque = F x LA

131 1

33

F x LA = Torque = F x LA

You can get the SAME TORQUE (door opens) by pushing with diff. forces!

Try #8-10 Check in at STOPSIGN.

Then, do #11.Check in your TEXT.

Finally, do #12.

You have 5 minutes 

What is different from scenario 1 to scenario 2? Which has more torque and why?

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0% A. 1 because the hand is angledB. 1 because more forceC. 1 because smaller lever armD. 1 because larger lever armE. 2 because the hand is perpendicularF. 2 because more forceG. 2 because smaller lever armH. 2 because larger lever armI. Same torque J. Not sure/ not enough info

What is different from scenario 2 to scenario 3? Which has more torque and why?

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0% A. 3 because the hand is angledB. 3 because more forceC. 3 because smaller lever armD. 3 because larger lever armE. 2 because the hand is perpendicularF. 2 because more forceG. 2 because smaller lever armH. 2 because larger lever armI. Same torque J. Not sure/ not enough info

9. Can the same force produce different amounts of torque?

If you apply the same force to different lever arms, you can get different torques!

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0% A. YesB. NoC. Not sure/not enough info

Or, if you apply the same force, but apply it at an angle vs. perpendicular!

10. Can the same torque be exerted from different forces?

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!

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0% A. YesB. NoC. Not sure/not enough info

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?

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

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0% A. YESB. NOC. IMPOSSIBLE TO SAY

12. When the CG is not over the area of support, what force produces a torque that causes toppling?

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0% A. Perpendicular forceB. GravityC. Support forceD. Not sure/ not enough info

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.

11.2 Balanced Torques

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

Calculations: 1. Calculate the girl’s torque:

a) What is the girl’s weight? (this is the Perpendicular Force)

b) What is the girl’s DISTANCE from the FULCRUM/TURNING POINT? (This is the Lever Arm)

c) Calculate the girl’s torque: *Show all work; the unit for torque is the Newton Meter ( Nm)

2.  Calculate the boy’s torque:a) What is the boy’s weight?

(this is the Perpendicular Force)

b) What is the boy’s DISTANCE from the FULCRUM/TURNING POINT? (This is the Lever Arm)

c) Calculate the boy’s torque: *Show all work; the unit for torque is the Newton Meter ( Nm)

200 N

3 m

F x LA = τ200 N x 3m = 600 Nm

400 N

1.5 m

F x LA = τ400 N x 1.5m = 600 Nm

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

11.2 Balanced Torques

do the math!What is the weight of the block hung at the 10-cm mark?

CAREFUL with your LEVER ARMS!!! 

11.2 Balanced Torques

11.2 Balanced 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 N x 30 cm

F x 40 cm = 600 N cm

Divide both sides by 40 cm ….

Force = 15 N

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

The broom balances at its CG.  If you cut the broom at its CG and weighed each side, which side would weigh more?

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F x LA = Torque = F x LAA. The broom HANDLE sideB. The broom BRUSH SIDEC. They weigh the sameD. Not sure/not enough info