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Work and Simple Machines

Work and Simple Machines. Work Answer the following questions with your elbow partner. What is work? Does everyone do work? We are going to contrast situations where work is done with different amounts of force to situations were no work is done For example:

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Work and Simple Machines

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  1. Work and Simple Machines

  2. WorkAnswer the following questions with your elbow partner. • What is work? • Does everyone do work? • We are going to contrast situations where work is done with different amounts of force to situations were no work is done • For example: • Moving a box with and without a ramp • Standing still

  3. What is work? • In science, the word work has a different meaning than you may be familiar with. • The scientific definition of work is: using aforce to move an object a distance • Both the force and the motion of the object are in the same direction. • Examples: pushing, pulling or lifting

  4. Work or Not? • According to the scientific definition, what is work and what is not? • a teacher lecturing to her class • a mouse pushing a piece of cheese with its nose across the floor

  5. Work or Not? • According to the scientific definition, what is work and what is not? • a teacher lecturing to her class • a mouse pushing a piece of cheese with its nose across the floor

  6. What’s work?Elbow partner time • A scientist delivers a speech to an audience of his peers. • A body builder lifts 350 pounds above his head. • A mother carries her baby from room to room. • A father pushes a baby in a carriage. • A girl pushes on a wall during PE.

  7. What’s work? • A scientist delivers a speech to an audience of his peers. • No • A body builder lifts 350 pounds above his head. • Yes • A mother carries her baby from room to room. • No • A father pushes a baby in a carriage. • Yes • A woman pushes on a wall during PE. • No

  8. Formula for work Work = Force x Distance • The unit of force is newtons (N) • The unit of distance is meters (m) • The unit of work is newton-meters (Nm) • One newton-meter is equal to one joule • So, the unit of work is a joule (J)

  9. W=FD Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done?

  10. W=FD Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done? 200 joules (W = 20N x 10m) White board practice time

  11. Work • Example # 1 What work is done to move a crate if the force applied is 345 N and the crate is moved 6 m?

  12. W=FxD 345 N, 6 M • W = ? • W = 345 N x ? • W = 345 N x 6 M • W = 2070 J

  13. Work • Example # 2 A fork lift moves 30m carrying a 1023N box across the warehouse floor. How much work is done by the fork lift.?

  14. W=F X D 1023 N, 30 m • W=FxD • W = ? • W= 1023 N x ? • W = 1023 N x 30 m • W = 30690 J

  15. Work • Example # 3 How much work is done by a person who uses a force of 27 N to move a grocery buggy 12 m?

  16. W=FxD 27 N,12m • W= FxD • W = 27 N x ? • W = 27 N x 12 m • W= 324 Nm • W = 324 J

  17. Example # 4 • How much work is done to lift a weight that has a mass of 75 N to a height of 2 m?

  18. W = F x D 75 N,2 m • W = F x D • W = 75 N x ? • W = 75 N x 2 m • W = 150 J

  19. History of Work Before engines and motors were invented, people had to do things like lifting or pushing heavy loads by hand. Using an animal could help, but what they really needed were some clever ways to either make work easier or faster.

  20. Simple Machines Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.

  21. Simple Machines Can you name the 6 simple machines from memory? • Inclined Plane • Pulley • Lever • Wheel and Axle • Wedge • Screw

  22. Simple Machines • A machine is a device that helps make work easier by changing: • the amount of force you exert • the distance over which you exert your force • The direction in which you exert your force

  23. Contrasting Work • You lift a 10 Newton box onto a moving truck that is 1.5 meters high. How much work did you do? • W= FxD • W= 10 N x 1.5 m • W= 15 Joules

  24. Contrasting Work • It takes 5 Newtons of force to push the same box onto a moving truck using a ramp that is 3 meters long. How much work did you do? (assume there is no friction on the ramp) • W= FxD • W= 5 N x 3 m • W= 15 Joules • The same amount of work is done but the ramp makes the work easier.

  25. Contrasting Work • You are leaning on one of the boxes you need to move with a force of 20 Newtons but the box doesn’t move. How much work is done? • W=FxD • W= 20 N x 0 m • W= 0 joules • No work done on the box

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