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Review

Review. To do the greatest amount of work, you must apply force (in the same direction, at an angle) that the object will move. If forces A, B, and C have equal strengths, force (A, B,C) will do the most work because it is entirely in the direction of the motion. In the same direction C.

jerry-johnson
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Review

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  1. Review • To do the greatest amount of work, you must apply force (in the same direction, at an angle) that the object will move. • If forces A, B, and C have equal strengths, force (A, B,C)will do the most work because it is entirely in the direction of the motion. • In the same direction • C

  2. Review- work • A crane lifts a steel beam with a mass of 1,500 kg. • Calculate how much work is done against gravity if the beam is lifted 50 meters in the air. • W= Fxd =1500 kg(9.8m/s²)(50m) =735 000 J

  3. It makes a difference how fast you do work.

  4. Review • A 70 kg person goes up stairs 5 m high in 30 sec. • a) How much power does the person need to use? Power= work/time =1143 W • b) Compare the power used with a 100-watt light bulb.

  5. Energy exists in many forms and all are able to convert to one another

  6. Energy- the property of an object that enables it to do work = All forms of energy are measured in Joules, a unit of force that acts over a distance • Energy is measured in the same units as work because energy is transferred during the action of work.

  7. Doing work always means transferring energy

  8. What would happen to the temp of the sand if you shook the container?

  9. Predict-what will happen when I drop the tennis ball and bb • 5 sentence persuasive essay You need to persuade your partner to drop the bb and tennis ball to demonstrate transfer of energy. Tell them why it is soooo cool to do this. Need 1) Topic sentence 2) 2 Facts 3) 1 opinion 4) Conclusion

  10. An example • 1) The weather helps everything in some way, shape or form. • 2) The weather lets the plants grow when it rains. • 3) It also provides us with drinkable water. • 4) The weather is a very nice thing to have around. • 5) In conclusion, the weather is very helpful and useful to us all.

  11. Mechanical Energy (Kinetic and potential)

  12. Potential Energy it has “the potential to do work”

  13. Potential energy • An object may store energy b/c of its position or shape it is stored or held in readiness

  14. Gravitational potential energy • Work is required to elevate objects against Earth’s gravity • The potential energy due to elevated positions is called PEg PEg =weight x height mg h

  15. (Gravitational) potential energy • http://shelf3d.com/Jnj8mc04r9E#Potential Energy: Wile E Coyote & Roadrunner • PEg= mgh =21 kg ( )(50 m) = 1 0290 J

  16. (Gravitational) Potential Energy • How much work is done by the snowboarder (70 kg)at the top of the mountain when he has moved 10 m horizontally? • When he has moved down the mountain 1000 m? • PEg= mgh =70 kg ( 9.8 m/s²)(1000 m) • = 686 000 Joules

  17. Kinetic energy It is “capable of doing work”

  18. Kinetic energy • The kinetic energy of a moving object depends on two things: mass and speed. KE= ½ mv²

  19. Kinetic energy • Mathematically, kinetic energy increases as the square of speed. KE= ½ mv² • If the speed of an object doubles, its kinetic energy increases four times. (mass is constant)

  20. KE= ½ mv² • Note that the speed is squared… so if the speed is double, the KE is quadrupled • 50 to 100 kph the braking distance of a car will increase from 10 metres to 40 metres

  21. When the brakes of a motorcycle traveling at 20 km/h become locked, how much farther will it skid if it travels at 60 km/h? • KE= sliding distance = 9x

  22. An assignment with your partner • You have 15 minutes to find 4 situations using potential and 4situations using kinetic energy • You will work in groups of 2 • You will draw them and label them. What is happening and where it occurred. • Use level 1 voices.

  23. Scavenger hunt EXAMPLES OF KINETIC ENERGY • Door closing 2) Room 123, English hall EXAMPLES OF POTENTIAL ENERGY

  24. Law of conservation of matter • As energy takes different forms and changes things by doing work, nature keeps perfect track of the total. • No new energy is created and no existing energy is destroyed.

  25. Law of conservation of energy • A wind turbine is turned with a constant force. How much work is done on the object? • The work done on the object is the same amount that is gained in kinetic and heat energy by the object

  26. Ke=Pe ½ mv² = mgh

  27. Work-energy theorem What does this picture tell us? http://www.pixton.com/comic/iq68urey

  28. WorkΔenergy theorem • Whenever work is done, energy changes • The amount of work done on an object= the amount of energy gained by the object

  29. An assignment with your partner • Draw 6 situations where there are energy transfers…you cannot use any examples from the powerpoints

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