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Chapter 15

Chapter 15. Energy. Windup Toy. http:// www.youtube.com/watch?v=xwCUzYuiTdk. Energy & Its Forms. 15.1. Avalanche Questions. Where did the energy of the avalanche come from? Where did it go?. Definitions. Work Done when a force moves an object through a distance A transfer of energy

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Chapter 15

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  1. Chapter 15 Energy

  2. Windup Toy • http://www.youtube.com/watch?v=xwCUzYuiTdk

  3. Energy & Its Forms 15.1

  4. Avalanche Questions • Where did the energy of the avalanche come from? • Where did it go?

  5. Definitions • Work • Done when a force moves an object through a distance • A transfer of energy • Energy • The ability to do work • Energy is transferred by a force moving an object through a distance

  6. Measuring Energy • SI Unit of Energy • Joules (J) • 1 Joule = 1 Newton-meter • Newton-meter • The work done when an object is moved 1 meter by 1-Newton force

  7. Two General Types of Energy Kinetic Energy Potential Energy Energy that is stored as a result of position or shape Energy with the potential to do work Examples: Lifting a book in the air Plucking a string • Energy of Motion • Depends on mass & speed • Formula

  8. Parts of KE Formula • K = Kinetic Energy (measured in Joules) • m = mass (measured in kilograms) • v = speed (measured in meters per second)

  9. Why would tripling the speed at which a car is moving have a greater effect on its kinetic energy than tripling its mass?

  10. KE Practice Problems • A 0.10 kg bird is flying at a constant speed of 8.0 m/s. What is the birds kinetic energy? • A 70.0 kg man is walking at a speed o 2.0 m/s. What is his kinetic energy? • A 1400 kg car is moving at a speed of 25 m/s. How much kinetic energy does the car have? • A 50.0 kg cheetah has a KE of 18,000 Joules. How fast is the cheetah running?

  11. Gravitational Potential Energy Gravitational PE Formula PE = mgh m = mass (kg) g = acceleration due to gravity (9.8 m/s2) h = height (meters) • PE that depends upon an object’s height • Increases as an object is raised to a higher level • Depends on an objects mass, height, and acceleration due to gravity

  12. Gravitational PE Practice Problems #1 #2 The same diver is standing on the ground. What is her gravitational PE? Why? • A diver is at the top of a 10.0 meter-high diving platform and has a mass of 50.0 kg. What is her gravitational PE?

  13. Elastic Potential Energy • The potential energy of an object that is stretched or compressed • Elastic means something springs back to its original shape after being stretched or compressed • Rubber bands… • Investigating Elastic PE Lab (p450)

  14. Forms of Energy • Mechanical Energy • Thermal Energy • Chemical Energy • Electrical Energy • Electromagnetic Energy • Nuclear Energy

  15. Mechanical Energy • Energy associated with the motion and position of everyday objects • Equal to the sum of KE and PE

  16. Thermal Energy • Matter is made of atoms that are in constant motion • The potential and kinetic energy of all of the atomic particles in an object make up its thermal energy

  17. Chemical Energy • The energy stored in chemical bonds • When bonds are broken, energy is released

  18. Electrical Energy • Energy associated with electrical charges

  19. Electromagnetic Energy • A form of energy that travels through space in the form of waves • The sun emits electromagnetic energy • Capable of traveling long distances in air and space

  20. Nuclear Energy • The energy stored in atomic nuclei • Nuclear energy can be used to generate electricity

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  34. Energy Conversion & Conservation 15.2

  35. An energy conversion story… • Meteor story, p 453 (read as class)

  36. Energy Conversion • Energy can be converted from one form to another • Energy conversion is the process of this change

  37. The story of a match… • Striking a match

  38. Conservation of Energy • Law of Conservation of Energy • Energy cannot be created nor destroyed • Energy changes from one form to another, but the total amount of energy remains unchanged

  39. An example… • You are riding your bike, pedaling at a constant rate, but then you stop pedaling and coast. You eventually come to a stop. Where did your kinetic energy go?

  40. PE to KE • Gravitational PE is converted to KE as an object falls to the ground • Elastic PE to KE… Slinky TIME!

  41. Energy story of a hungry sea gull… • Write a quick story about how a sea gull could crack open an oyster shell. • Energy terms to consider: Gravitational PE, KE, Chemical Energy (in the form of Gull food)

  42. Conversion Calculations • Mechanical Energy = PE + KE • Can be applied to any mechanical process (which is any action, for example, a sea gull flying an oyster high into the air and then dropping it on a rock) • In these calculations we assume friction is negligible

  43. Conservation of Mechanical Energy (KE + PE)Beginning = (KE + PE)End

  44. Conservation Example • At a construction site, a 1.50-kg brick is dropped from rest and hits the ground at a speed of 26.0 m/s. Assuming air resistance can be ignored, calculate the gravitational potential energy of the brick before it was dropped. At what height was the brick dropped from.

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