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Chapter 13

Chapter 13. WORK & ENERGY. TN Standards. CLE 3202.4.3 – Demonstrate the relationship among work, power, and machines CLE 3202.2.6 – Investigate the Law of Conservation of Energy. Bellwork. What is Work?. Work, Power, and Machines.

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Chapter 13

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  1. Chapter 13 WORK & ENERGY

  2. TN Standards • CLE 3202.4.3 – Demonstrate the relationship among work, power, and machines • CLE 3202.2.6 – Investigate the Law of Conservation of Energy

  3. Bellwork • What is Work?

  4. Work, Power, and Machines • Work is conducted only when an applied ( net ) force results in the change in position of an object • Work is measured in Joules ( J ) • Work is calculated by multiplying force and distance ( over which the force is applied ) • W = F x d

  5. Work, Power, and Machines • Power is the amount of work conducted over a certain time interval • P = W / Δt • Power is measured in Watts

  6. Work, Power, and Machines • Machines help to do work by changing the size of an input force, the direction of a force, or both • Different forces can do the same amount of work • Figure 3 ( a box lifted vs a box pushed up a ramp )

  7. Simple Machines • The six types of simple machines are: • Simple lever • Wheel and axle • Pulley • Simple inclined plane • Wedge • Screw

  8. Compound Machines • A combination of any of those six simple machines • Example – SCISSORS • Combination of lever and wedge

  9. Bellwork • What is Energy?

  10. What is Energy? • Energy is a property of an object due to its motion or its position • When work is done, energy is transferred or transformed from one system to another • Carry a tennis ball up in the stadium • You add potential energy to it by carrying it up

  11. What is Energy? • Energy is measured also in Joules ( J ) • Potential energy – energy of position • PE = hmg • h is height ; g is gravity; m is mass • Height is relative • Kinetic Energy – energy of motion • KE = ( ½ ) mv2 • m is mass ; v is velocity

  12. Other Forms of Energy • Mechanical energy • Non-mechanical energy • ( atomic level ) • Chemical reactions involves chemical energy ( a form of potential energy ) • Sun gets energy from nuclear reactions • Electrical energy ( stored in electric fields )

  13. Conservation of Energy • Energy easily changes from one form to another ( battery ) • PE can become KE ( tennis ball dropped from the top of stadium ) • Vice-versa ( projectile shot / reaches max height ) • Law of Conservation of Energy? • ( neither created nor destroyed )

  14. Roller Coaster Example

  15. Thermodynamics • For any system, the net change in energy equals the energy transferred as work and heat • Efficiency ( how much energy/work you get out of a machine or process compared to how much is put in ) • Internal Combustion Engine

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