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1 Work and Simple Machines

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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: Moving a box with and without a ramp Moving a box with and without a ramp Standing still Standing still

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

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4 Work or Not? According to the scientific definition, what is work and what is not? a teacher lecturing to her class a teacher lecturing to her class 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

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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

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7 What’s work? Elbow partner time 1. A scientist delivers a speech to an audience of his peers. 2. A body builder lifts 350 pounds above his head. 3. A mother carries her baby from room to room. 4. A father pushes a baby in a carriage. 5. A girl pushes on a wall during PE.

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What’s work? 1. A scientist delivers a speech to an audience of his peers. No No 2. A body builder lifts 350 pounds above his head. Yes Yes 3. A mother carries her baby from room to room. No No 4. A father pushes a baby in a carriage. Yes Yes 5. A woman pushes on a wall during PE. No No

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9 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)

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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?

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11 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

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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?

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W=FxD345 N,6 M W = ? W = 345 N x ? W = 345 N x 6 M W = 2070 J

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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.?

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

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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?

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W=FxD27 N,12m W= FxD W = 27 N x ? W = 27 N x 12 m W= 324 Nm W = 324 J

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

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W = F x D75 N,2 m W = F x D W = 75 N x ? W = 75 N x 2 m W = 150 J

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20 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.

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

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

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

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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= 10 N x 1.5 m W= 15 Joules W= 15 Joules 24

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Contrasting Work 25 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= 5 N x 3 m W= 15 Joules W= 15 Joules The same amount of work is done but the ramp makes the work easier. The same amount of work is done but the ramp makes the work easier.

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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 26

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