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Section 4.1 - The Nature of Energy

Section 4.1 - The Nature of Energy. What Is Energy?. Changes are constantly occurring in the world. Examples: light bulbs heating the air, sunlight on window, you breathing Every change requires energy. Energy – ability to cause change. Energy is Found in Many Forms.

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Section 4.1 - The Nature of Energy

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  1. Section 4.1 - The Nature of Energy

  2. What Is Energy? • Changes are constantly occurring in the world. • Examples: light bulbs heating the air, sunlight on window, you breathing • Every change requires energy. • Energy – ability to cause change

  3. Energy is Found in Many Forms • Electromagnetic energy – energy in waves • Examples: UV, Infrared, Radio • Mechanical – energy in physical movement • Examples: moving car, flying baseball • Electrical energy – energy carried by movingelectrons • Heat – thermal energy • Example: cup of hot tea

  4. Energy is Found in Many Forms • Chemical – stored in molecules • Example: food, batteries • Nuclear – energy stored in the nucleus of an atom • Example: Uranium used in nuclear reactors • Kinetic – energy an object in motion has • Example: person running, roller coaster going down a hill • Potential – stored energy due to an object’s position • Example: roller coaster at the top of a hill

  5. Units of Energy – the Joule • Units of energy • Symbol: J • J = kg x m2/s2 James Prescott Joule

  6. Kinetic Energy • Energy that a moving object has because of its motion. • Depends on an object’s mass and its speed. KE = ½ mv2 KE: kinetic energy in Joules (J) m: mass in kg v: velocity (m/s)

  7. Kinetic Energy – 3 Equations KE = ½ mv2 1 m = 2( ) KE 2 v2 v = √2( ) KE 3 m

  8. Examples of Solving for Kinetic Energy • A jogger with a mass of 60 kg is moving at a speed of 3 m/s. What is the kinetic energy?

  9. Examples of Solving for Kinetic Energy • A bowling ball is moving with 300 J of energy. The ball weighs 2 kg. How fast is the ball moving?

  10. Potential Energy • Stored energy due to an object’s position • Three types: • Elastic potential energy – energy stored by something that can stretch or compress • Chemical potential energy – energy stored in chemical bonds • Gravitational potential energy – energy stored in objects due to their position above the Earth’s surface

  11. Solving for Potential Energy GPE = mgh GPE: gravitational potential energy (J) m: mass (kg) g: 9/8 m/s2 h: height (m)

  12. Potential Energy GPE = mgh 1 m = GPE 2 gh h = GPE 3 mg g = GPE 4 mh

  13. Examples of Solving for Potential Energy • What is the gravitational potential energy of a ceiling fan that has a mass of 7 kg and is 4 m above the ground? GPE = mgh GPE = 7 kg (9.8)(4 m) GEP = 274.4 J

  14. Examples of Solving for Potential Energy • How high above the ground is a baseball with a mass of 0.15 kg and a GPE of 73.5 J? h = GPE mg h = 73.5 J/ (0.15 kg x 9.8) h = 50 m

  15. Changing GPE • As an object begins to fall it has GPE and KE. • As the object gets closer to the ground it has less GPE and more KE.

  16. Changing GPE • Example – An 80 kg skydiver jumps from a 10 m platform. What is the GPE of the skydiver at the top of the platform? What is the GPE of skydiver after falling 5 m? GPE = mgh GPE = 80 kg (9.8)(5 m) GEP = 3920 J GPE = mgh GPE = 80 kg (9.8)(10 m) GEP = 7840 J

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