Energy: Forms and Changes

1. Energy: Forms and Changes

2. Nature of Energy • Energy is all around you! • You can hear energy as sound. • You can see energy as light. • And you can feel it as wind.

3. Nature of Energy • You use energy when you: • hit a softball. • lift your book bag. • compress a spring.

4. Nature of Energy Living organisms need energy for growth and movement.

5. Nature of Energy • Energy is involved when: • a bird flies. • a bomb explodes. • rain falls from the sky. • electricity flows in a wire.

6. Nature of Energy • What is energy that it can be involved in so many different activities? • Energy can be defined as the ability to do work. • If an object or organism does work (exerts a force over a distance to move an object) the object or organism uses energy.

7. Nature of Energy • Because of the direct connection between energy and work, energy is measured in the same unit as work: joules (J). • In addition to using energy to do work, objects gain energy because work is being done on them.

8. Forms of Energy • The seven main forms of energy are: • Thermal • Chemical • Radiant • Nuclear • Mechanical • Sound • Electric

9. Thermal Energy • The internal motion of the atoms is called thermal energy, because moving particles produce heat. • Thermal energy can be produced by friction. • Thermal energy causes changes in temperature and phase of any form of matter.

10. Chemical Energy • Chemical Energy is required to bond atoms together. • And when bonds are broken, energy is released.

11. Chemical Energy • Fuel and food are forms of stored chemical energy.

12. Electromagnetic Energy • Light is a form of electromagnetic energy. • Each color of light (Roy G Bv) represents a different amount of electromagnetic energy. • Electromagnetic Energy is also carried by X-rays, radio waves, and laser light.

13. Nuclear Energy • The nucleus of an atom is the source of nuclear energy.

14. Nuclear Energy • When the nucleus splits (fission), nuclear energy is released in the form of heat energy and light energy. • Nuclear energy is also released when nuclei collide at high speeds and join (fuse).

15. Nuclear Energy The sun’s energy is produced from a nuclear fusion reaction in which hydrogen nuclei fuse to form helium nuclei.

16. Nuclear Energy • Nuclear energy is the most concentrated form of energy.

17. Mechanical Energy • When work is done to an object, it acquires energy. The energy it acquires is known as mechanical energy.

18. Energy Conversion • Energy can be changed from one form to another. Changes in the form of energy are called energy conversions.

19. Energy conversions • All forms of energy can be converted into other forms. • The sun’s energy through solar cells can be converted directly into electricity. • Green plants convert the sun’s energy (electromagnetic) into starches and sugars (chemical energy).

20. Other energy conversions • In an electric motor, electromagnetic energy is converted to mechanical energy. • In a battery, chemical energy is converted into electromagnetic energy. • The mechanical energy of a waterfall is converted to electrical energy in a generator.

21. Energy Conversions • In an automobile engine, fuel is burned to convert chemical energy into heat energy. The heat energy is then changed into mechanical energy.

22. Chemical  Heat Mechanical

23. States of Energy • The most common energy conversion is the conversion between potential and kinetic energy. • All forms of energy can be in either of two states: • Potential • Kinetic

24. States of Energy: Kinetic and Potential Energy • Kinetic Energy is the energy of motion. • Potential Energy is stored energy.

25. Potential Energy • Potential Energy is stored energy. • Stored chemically in fuel, the nucleus of atom, and in foods. • Or stored because of the work done on it: • Stretching a rubber band. • Winding a watch. • Pulling back on a bow’s arrow. • Lifting a brick high in the air.

26. Gravitational Potential Energy • Potential energy that is dependent on height is called gravitational potential energy.

27. Potential Energy • Energy that is stored due to being stretched or compressed is called elastic potential energy.

28. Gravitational Potential Energy • A waterfall, a suspension bridge, and a falling snowflake all have gravitational potential energy.

29. Gravitational Potential Energy • If you stand on a 3-meter diving board, you have 3 times the G.P.E, than you had on a 1-meter diving board.

30. Gravitational Potential Energy • “The bigger they are the harder they fall” is not just a saying. It’s true. Objects with more mass have greater G.P.E. • The formula to find G.P.E. is G.P.E. = Weight X Height.

31. Let’s Practice A flower pot with a mass of 15 kg is sitting on a window sill 15 meters above the ground. How much potential energy does the flower pot contain? • PE = (mass)(gravity)(height) • = (15 kg)(9.8 m/s2)(15 m) • = 2205 kg • m2/s2 or J

32. Let’s Practice A rock has a mass of 8.40 x 104 kg. The center of mass is 29.0 m above the ground. How much energy does it have? PE = mgh Identify the variables m= 8.40 x 104 kg g= 9.81 m/s2 h= 29.0 m PE = (8.4X104)(9.81)(29) = 2.39 x 107 J http://gaaf.com/pictures/200406_utah/image009.htm

33. Kinetic Energy • The energy of motion is called kinetic energy. • The faster an object moves, the more kinetic energy it has. • The greater the mass of a moving object, the more kinetic energy it has. • Kinetic energy depends on both mass and velocity.

34. Kinetic Energy K.E. = mass x velocity 2 What has a greater affect of kinetic energy, mass or velocity? Why? 2

35. Let’s Practice What is the kinetic energy of this car when it is traveling 38.0 m/s? What other information do you need? KE = ½ m v2 = ½ (1550)(38.0)2 = 1119100 J = 1.11 x 106 J Car’s mass = 1550kg

36. Let’s Practice A bicycle with a mass of 14 kg traveling at a velocity of 3.0 m/s east has how much kinetic energy? KE = 0.5mv2 m = 14 kg v = 3.0 m/s E = 0.5(14 kg)(3.0 m/s)2 = 0.5(14 kg)(9.0 m2/s2) = 63 kg• m2/s2 = 63 J

37. Kinetic-Potential Energy Conversion Roller coasters work because of the energy that is built into the system. Initially, the cars are pulled mechanically up the tallest hill, giving them a great deal of potential energy. From that point, the conversion between potential and kinetic energy powers the cars throughout the entire ride.

38. Recap • Energy in a system may take on various forms (e.g. kinetic, potential, thermal, radiant). • The law of conservation of energy states that energy may neither be created nor destroyed. • Therefore the sum of all the energies in the system is a constant.

39. Kinetic vs. Potential Energy At the point of maximum potential energy, the car has minimum kinetic energy.

40. Kinetic-Potential Energy Conversions • As a basketball player throws the ball into the air, various energy conversions take place.

41. Ball speeds up Ball slows down

42. The Law of Conservation of Energy • Energy can be neither created nor destroyed by ordinary means. • It can only be converted from one form to another. • If energy seems to disappear, then scientists look for it – leading to many important discoveries.

43. Law of Conservation of Energy • In 1905, Albert Einstein said that mass and energy can be converted into each other. • He showed that if matter is destroyed, energy is created, and if energy is destroyed mass is created. 2 • E = MC

44. The most commonly used example of conservation of energy is the pendulum:

45. Mechanical Energy The sum of PE and KE is the total mechanical energy: ME = PE + KE

46. NOTE: This is with the absence of outside forces such as friction • Using our common sense we know that it's impossible for the pendulum to swing higher than the height h without giving it a push yourself. • If there was no friction, the pendulum would swing back and forth forever because of the law of conservation of energy.

47. Let’s practice • A 2.0 kg toy dump truck moving with a speed of 3.0 m/s starts up a ramp. How high does the car roll before it stops? • Pe(top) = Ke(bottom) • mgh = 1/2mv2 or gh = 1/2v2 • 9.8 * h = ½(3)2 • h = 0.459 m