1. Part II – Torque & Simple Machines
Chapter 7

2. Why aren’t doorknobs in the middle?
Torque
Ability to turn something depends on angle applied and distance from pivot as well as size of force

3. Torque Torque = Force times lever arm T = Fd*
Can only use the part of the force perpendicular to the lever arm
Units: N·m

4. Torque

5. Torque Examples Force produces acceleration Torque produces rotation
How can you maximize torque?
Pipe wrench, screwdriver

6. Balanced Torques Examples: Seesaw f D = F d
ex: Where would a 600 N boy have to sit in order to balance a 200 N girl who sits 3 m from the fulcrum?

7. Balanced Torques Examples: Scale Balances
ex: Suppose that a meterstick is supported at the center, and a 20 N block is hung at 80 cm. Another block of unknown weight balances the system at the 10 cm mark. What is the weight of the second block?

8. Simple Machines Purpose of machines? 2 possible purposes
Change direction of force
Multiply force
NEVER does more work

9. Simple machines (6 of them)
Lever Examples?
Inclined Plane Examples?
Pulley Examples?
Wheel & Axle Examples?
Wedge Examples?
Screw Examples?

10. Simple Machine Examples
Seesaw, lever
Pipe wrench, wheels
“Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.” Archimedes

11. Simple Machines Mechanical advantage - Force out divided by force in
MA = Fout/Fin
If ignoring friction – Din/Dout

12. Simple Machines Efficiency – does the machine lose a lot of energy?
Work in should equal work out
Win = Fin*Din = Fout*Dout = Wout
Friction says Win > Wout
Efficiency = Wout / Win