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Do Now: A 2.5-kg rock loses 375 J of potential energy while falling to the ground. What is the rock's speed just before it strikes the ground?

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Simple Machines 2/9/11

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Machine: A machine eases the load by changing either the magnitude or the direction of a force to match the force to the capability of the machine of the person

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Lever A lever is a stiff bar that rests on a support called a fulcrum which lifts or moves loads.

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Pulley A pulley is a simple machine that uses grooved wheels and a rope to raise, lower or move a load

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Wheel and Axle A wheel with a rod, called an axle, through its center lifts or moves loads.

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Inclined Plane An inclined plane is a slanting surface connecting a lower level to a higher level.

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Wedge A wedge is an object with at least one slanting side ending in a sharp edge, which cuts material apart.

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Screw A screw is an inclined plane wrapped around a pole which holds things together or lifts materials.

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Do Now (2/8/12): Identify at least two examples of each of the following simple machines: 1. Lever 2. Pulley 3. Wheel and axle

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Machines Machines make work easier by decreasing the force required The work stays the SAME; the distance increases W = F d d

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Mechanical Advantage The ratio of the resistance force to the effort force Force of resistance: weight of load Effort force: force exerted

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Ideal Machines Transfer all energy; work input = work output

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Ideal Mechanical Advantage

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Efficiency

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Examples Please take out your Simple Machines worksheet

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Practice Please use the rest of class to work on the paper “Machines.” It is due on Friday! *note – unit test on Energy, Work and Power will be on Tuesday, February 14 th.

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Efficiency 3 formulas

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Do Now (2/9/12): A worker is testing a pulley system to find the heaviest object that he could lift. The largest force that he could exert is 380 N. When the worker moves the rope 3 m, the object moves.65 m. 1. What is the heaviest object he could lift? 2. What is the mechanical advantage? 3. What is the IMA? 4. What is the efficiency?

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Agenda: 1. 3 rd quarter project 2. Finish up homework 3. Begin working on notecards for test

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Do Now (2/10/12): A worker is testing a pulley system. The largest force that he could exert is 320 N. When the worker moves the rope 4 m, the object moves.75 m. The weight lifted is 540 N. 1. What is the mechanical advantage? 2. What is the IMA? 3. What is the efficiency?

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Pass in: homework Do Now’s

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Work Work at an angle

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Do Now (punks!): A physics book of unknown mass is dropped from a height of 6 m. what is the speed of the book before it hits the ground?

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Do Now: 1. If a 2kg object drops 50 m, how much potential energy did it lose? 2. What is its kinetic energy at the bottom?

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