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Chapter 10: Work, Energy, and Simple Machines

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Work No it’s not your job! Work is the product of force and the distance an object moves in the direction of force Scalar quantity- no direction Measured in Joules A JOULE is 1 newton of force times one meter of movement The object must MOVE or there is no work, only force

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Work Work only occurs if the force and displacement are in the same direction Increasing the force or the displacement, increases the work done on an object FORMULA FOR WORK W = Fd Work = Force times displacement Example problem #1 Practice problems #1-3

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Work and the direction of force Force must be exerted in the direction of motion for work to be done If the force is perpendicular to the motion- NO WORK IS DONE!!! The object that exerts the force does the work

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Work and angles of force What happens when the force is at an angle to the motion? – Use the amount of force acting on the direction of motion – Use the formula W = Fd(cos ) to determine the amount of force in the direction of motion – If the work is negative- the object is doing work on another object – If the work is positive- work is being done on the object

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Work and angles of force The effect of doing work is the transfer of energy from one object to another Work is the mechanical transfer of energy

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Steps for solving work problems 1.Carefully check the forces acting on the object – You may use vector diagrams to do this 2.Determine the displacement and any angle between the force and the direction of motion 3.Check the sign (+ or -) by determining the direction energy is transferred – If the sign is positive energy has increased – If the sign is negative energy has decreased

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Practice Example problem #2 Practice problems #5-7

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Power Work does not consider time Work to move a stack of 10 objects 1m is the same whether you move each object in 2 seconds or 10 seconds. POWER is the rate work is done- more power is required to move the stack of 10 objects in 2 seconds than is required to move the same stack in 10 seconds Power is work done divided by the time it takes to do the work P = W/t Measured in watts or kilowatts 1 watt = 1 joule per second

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Practice Example #3 Practice problems 9-11 Lab- Page 204

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Simple Machines

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