Energy and Energy Resources

1. Energy and Energy Resources • Students will be familiar with the forms and transformations of energy

2. Learning Objectives • Explain the relationship between potential and kinetic energy. • Compare and contrast the different forms of energy (heat, light, electricity, mechanical motion, sound) and their characteristics. • Explain energy transformation in terms of the Law of Conservation of Energy. • Describe how heat can be transferred through matter by the collisions of atoms (conduction) or through space (radiation). In a liquid or gas, currents will facilitate the transfer of heat (convection). • Describe the movement of particles in solids, liquids and gases. • Describe the exchange of energy in physical changes of state

3. What is Energy? • Energy is the ability to do work • Work is defined as moving an object a distance W = Fx D and is expressed in joules (N/m) • As work is done on an object, energy is transferred • Energy is expressed in joules (J) also.

5. KINETIC ENERGY • Kinetic energy is energy due to motion • Book example: KE allows the hammer to do work on the nail

6. KE depends on mass and speed • KE = mv2 or ½(mv2) • 2 • The more mass, the more KE • The more speed, the more KE • Which is easier to roll? A bowling ball or a golf ball?

7. CALCULATE: • What is the KE of a car that has a mass of 1200 kg and is moving at 20 m/s? • Remember KE = mv2 2

8. KE = 1200 kg x (20 m/s)2 2 = 1200kg x 400 m2/s2 2 = 480,000 kg x m2/s2 2 = 240,000 Joules

9. CALCULATE: • How would the KE change if the mass of an object is doubled? • How would the KE increase if an object doubled its speed? • It would change by 22 or 4 times as much

10. POTENTIAL ENERGY • Energy that an object has due to its position. (stretched bow or a rubber band) • Gravitational Potential Energy • Work was done on an object to lift it up against gravity • GPE = weight x height • GPE = m x g x h

11. Problems • What is the GPE of a book with a weight of 13N and is 1.5m off the floor? GPE = Wt. x H GPE = 13N x 1.5m GPE = 19.5 J • What if the mass of the book is 50g? • GPE = m x g x h • GPE = 50g x 9.8m/s2 x 1.5

13. MECHANICAL ENERGY • The total energy of motion and position of an object • Mechanical energy = kinetic energy + potential energy • ME = KE + PE

14. Mechanical energy can be: • All potential energy • All kinetic energy • A combination of the two Mechanical energy does not change!

15. Other Forms of Energy • Energy exists in different “forms”

16. CHEMICAL ENERGY • Energy comes from the rearrangement of atoms when new compounds form • Chemical energy can be stored

17. ELECTRICAL ENERGY • Energy comes from moving electrons • Energy is transferred from a power plant through wires

18. SOUND • Where does its energy come from? • Energy comes from an object’s vibrations – travels in waves • Ex. Strings on instruments cause the air molecules around them to vibrate. Vibrations carry the sound to our ears • Sound requires matter to transfer energy

19. NUCLEAR ENERGY Where does the energy come from? Energy that comes from changes in the nucleus of an atom

20. How is energy given off from the nucleus? • When two nuclei join, called fusion Ex. hydrogen joining to form helium

21. How is energy given off from the nucleus? • When the nucleus splits apart, called fission Ex. In nuclear reactors; making nuclear weapons

22. LIGHT ENERGY • Where does the energy come from? • Energy comes from vibrations in electrically charged particles • “electromagnetic” waves- has some electrical and magnetic properties

23. Invisible light? • Not all light can be seen • Light does NOT need matter to transfer energy. • Light energy can transfer through empty space

24. THERMAL ENERGY • Depends on the motion of the molecules AND how many molecules are present.

25. WHAT DOES THAT MEAN? • Higher temperature = more thermal energy • Larger amount of a substance = more thermal energy

26. Thermal Energy in Water Which illustration has more thermal energy?

27. Which has more thermal energy? The tea in the teapot? or the tea in the cup?

28. Conservation of Energy • Energy is not created or destroyed • In a closed system, the quantity of energy remains the same • It can change forms: mechanical to thermal – rubbing hands electrical to light & thermal- light bulb

29. Einstein Disagrees! • Theory or Relativity: • Energy can sometimes be created by destroying matter Nuclear reactions- tiny amounts of matter create large amounts of energy Matter and energy together are always conserved!

30. Temperature • The measure of the average kinetic energy of a substance • All matter has kinetic energy • But different particles move at different speeds Temperature does not depend on how much of the substance there is

31. Temperature can be measured because of thermal expansion of the liquid in the thermometer • when temperature increases, the particles spread out and take up more space (volume) • thermometers use alcohol or mercury • expansion joints are used in highways • thermostats rely on thermal expansion (p.278)

32. Review the Temperature Scales!!

33. What is Heat? • the transfer of thermal energy from one object to another • always moves from warm to cool on contact • eventually equilibrium is reached- the transfer will stop when both objects reach the same temperature

35. THERMAL ENERGY TRANSFER • Heat is the transfer of energy from one substance to another • It transfers from the warmer object to the cooler object • The transfer will end when both objects reach the same temperature

36. THREE WAYS TO TRANSFER THERMAL ENERGY • Conduction • Convection • Radiation

37. CONDUCTION • Particles from a warmer object transfer by colliding with particles from the cooler object.

38. CONDUCTORS AND INSULATORS • Substances that conduct thermal energy very well are conductors Substances that do not conduct thermal energy very well are insulators

39. CONVECTION • Transfer of thermal energy by the movement of a liquid or a gas

40. RADIATION • Thermal energy transferred through electromagnetic waves • Visible light, ultraviolet, infrared, x-rays…..

41. The Greenhouse Effect

42. Matter and Heat • state of matter is a physical property • The state depends on the speed of the matters particles

43. Change of State • A physical change- does not change the identity of the substance • ex. ice = water= steam (it is all H20)

44. Change of state involves change in energy: • popsicle melts when you hold it • dew covers a windshield • rain puddle disappears • bathroom mirror fogs up • wintery road becomes slippery at night