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**Chapter 8: Work, Power, Simple machines**

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**Section 1: Work and Power**

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**1) In science, work occurs when a force causes an object to move in the direction of the force.**

Work has happened because the box moved

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2) Work is done when the object moves as the force is applied and b) the direction of the object’s motion is the same as the direction of the force applied.

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**3) Work can be calculated:**

W=F x d Work equals force times distance

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**4) Force is measured in Newtons, and distance is measured in meters:**

so the unit for work is the Newton-meter or the joule.

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5) Calculating work: a) A man applies a force of 500N to push a truck 100m down the street. How much work does he do?

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**1- You lift a 75N bowling ball 2 m off the floor**

b) In which situation do you do more work? 1- You lift a 75N bowling ball 2 m off the floor 2- You lift two 50 N bowling balls 1m off the floor.

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**Complete the following work problems**

Complete the following work problems. The first one has been done as an example for you. Work (J) = Force (N) X Distance (m) 1. 20J = 10N X 2m 2. 20J = force? X 2m 3. work? = 10N X 50m 4. work? = 0.5N X 600m 5. 500J = 500N X distance? 6. work? = 80N X 7m

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**the units for power are the watt (W)**

6) Power is how fast work is done. It can be calculated: P=W/t the units for power are the watt (W)

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**a) work is done in less time, or b) the amount of work is increased.**

7) Power is increased if a) work is done in less time, or b) the amount of work is increased. Review game

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Section 2: Machines

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**A machine is a device that helps make work easier**

Machines change either the size or direction of a force.

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**2) Machines do not make work less; they make work easier,**

and this is called the mechanical advantage.

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**3) Work done on a machine is called work input, work done by the machine is the work output.**

Work output is never greater than work input, because some of the work done by the machine is used to overcome friction.

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**4) The less work a machine has to do to overcome friction the more efficient it is.**

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**Section 3: Types of Machines**

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1) All machines are made from six simple machines: the lever, inclined plane, wedge, screw, pulley, and wheel and axle.

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**2) Levers: a bar that pivots at a fixed point called a fulcrum**

A) First class levers: fulcrum between the input force and load (see-saw) B) Second class levers: load between the fulcrum and the input force (wheel barrow) C) Third class levers: input force between the fulcrum and the load (hammer)

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3) Inclined Plane: straight slanted surface - the longer the plane the greater the mechanical advantage (ramp)

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**4) Wedges: double inclined plane that moves (knife or scissors)**

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**5) Screw: inclined plane wrapped in a spiral**

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**6) Wheel and axle: two circular objects of different sizes (door knobs)**

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7) Pulleys: grooved wheel that holds a rope or cable, with a load attached to one end, input force applied to another

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**8) Compound machines: machines made of two or more simple machines**

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