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Chapter 10: Work, Energy, and Simple Machines

Chapter 10: Work, Energy, and Simple Machines. 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

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Chapter 10: Work, Energy, and Simple Machines

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  1. Chapter 10: Work, Energy, and Simple Machines

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. Steps for solving work problems • Carefully check the forces acting on the object • You may use vector diagrams to do this • Determine the displacement and any angle between the force and the direction of motion • 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

  8. Practice • Example problem #2 • Practice problems #5-7

  9. 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

  10. Practice • Example #3 • Practice problems 9-11 • Lab- Page 204

  11. Simple Machines

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