1. Work and Simple Machines

2. Work When a force causes an object to move – work is done. When a force causes an object to move – work is done.

3. Work cont. Work = Force x distance Or W = F x d

4. If the object does not move then no work is done. If the object does not move then no work is done. W = F x d If d = 0 any number times 0 is 0 so no work.

5. Work also depends on direction. Work also depends on direction. The force has to be in the same direction as the motion or no work is done on the object. The force has to be in the same direction as the motion or no work is done on the object. Lifting the Books Force Work is done Carrying the Books Force & Motion The same perpendicular Work is Not Done & Motion

6. The SI unit for work is joules (J) 1 J = 1kg x m 2 /s 2 = 1 Nm F = N= kg m/s 2 d = m So W = F x d = Nm

7. Work or Not? Carrying a box across the ramp Carrying a box across the ramp a mouse pushing a piece of cheese with its nose across the floor a mouse pushing a piece of cheese with its nose across the floor

8. What’s Work? A scientist delivers a speech to an audience of his peers. A scientist delivers a speech to an audience of his peers. A body builder lifts 350 pounds above his head. A body builder lifts 350 pounds above his head. A mother carries her baby from room to room. A mother carries her baby from room to room. A father pushes a baby in a carriage. A father pushes a baby in a carriage. A woman carries a 20 kg grocery bag to her car? A woman carries a 20 kg grocery bag to her car?

9. What’s Work? A scientist delivers a speech to an audience of his peers. No A scientist delivers a speech to an audience of his peers. No A body builder lifts 350 pounds above his head. Yes A body builder lifts 350 pounds above his head. Yes A mother carries her baby from room to room. No A mother carries her baby from room to room. No A father pushes a baby in a carriage. Yes A father pushes a baby in a carriage. Yes A woman carries a 20 km grocery bag to her car? No A woman carries a 20 km grocery bag to her car? No

10. Work Work is the Work is the transfer of energy through motion transfer of energy through motion force exerted through a distance force exerted through a distance W = Fd Distance must be in direction of force! W:work (J) F:force (N) d:distance (m) 1 J = 1kg x m 2 /s 2 = 1 Nm

11. Work Brett’s backpack weighs 30 N. How much work is done on the backpack when he lifts it 1.5 m from the floor to his back? GIVEN: F = 30 N d = 1.5 m W = ? WORK: W = F·d W = (30 N)(1.5 m) W = 45 J F W d

12. Work If it takes 375 J of work to push a box 75 m what is the force used to push the box? GIVEN: d = 75 m W = 375 J or 375 Nm F = ? WORK: F = W/d F =(375 Nm)/(75m) F = 5.0 N F W d

13. Making Work Easier The Simple Machines  Lever  Pulley  Wheel & Axle  Inclined Plane  Screw  Wedge

15. Machine – a device that makes doing work easier by…

16.  increasing the force that can be applied to an object. (car jack)

17.  increasing the distance over which the force can be applied. (ramp)

18.  by changing the direction of the applied force. (opening the blinds)

19. A. Lever Lever Lever a bar that is free to pivot about a fixed point, or fulcrum. a bar that is free to pivot about a fixed point, or fulcrum. “Give me a place to stand and I will move the Earth.” – Archimedes Engraving from Mechanics Magazine, London, 1824 Effort (input) arm You apply your force Resistance (output) Arm Work is done here. Fulcrum

20. First Class Lever First Class Lever First Class Lever the fulcrum is in the middle the fulcrum is in the middle changes direction of force changes direction of force Ex: pliers, seesaw Ex: pliers, seesaw

21. Second Class Lever Second Class Lever Second Class Lever The output (resistance) is in the middle The output (resistance) is in the middle always increases force always increases force Ex: wheelbarrow, nutcracker Ex: wheelbarrow, nutcracker

22. Third Class Lever Third Class Levers Third Class Levers Input (effort) force is in the middle Input (effort) force is in the middle always increases distance always increases distance Ex: tweezers, bat, human body Ex: tweezers, bat, human body

23. Think FOIL Fulcrum in middle = 1 st class lever Fulcrum in middle = 1 st class lever Output in middle = 2 nd class lever Output in middle = 2 nd class lever Input in middle = 3 rd class lever Input in middle = 3 rd class lever LEVERS LEVERS

24. B. Pulley Pulley Pulley grooved wheel with a rope or chain running along the groove grooved wheel with a rope or chain running along the groove a “flexible first-class lever” a “flexible first-class lever” LeLe LrLr F

25. C. Wheel and Axle Wheel and Axle Wheel and Axle two wheels of different sizes that rotate together two wheels of different sizes that rotate together a pair of “rotatinglevers” a pair of “rotatinglevers” effort force is applied to effort force is applied to wheel wheel axle moves less distance but with greater force axle moves less distance but with greater force Wheel Axle

26. D. Inclined Plane Inclined Plane Inclined Plane sloping surface used to raise objects sloping surface used to raise objects Ramps, mountain roads Ramps, mountain roads h l

27. E. Screw Screw Screw inclined plane wrapped in a spiral around a cylinder inclined plane wrapped in a spiral around a cylinder

28. F. Wedge Wedge Wedge a moving inclined plane with 1 or 2 sloping sides a moving inclined plane with 1 or 2 sloping sides

29. F. Wedge Zipper Zipper 2 lower wedges push teeth together 2 lower wedges push teeth together 1 upper wedge pushes teeth apart 1 upper wedge pushes teeth apart

30. F. Wedges