15 2 Energy Conversion and Conservation 15 2

15. 2 Energy Conversion and Conservation 15. 2 Key Concepts • Can energy be converted from one form to another? • What is the law of conservation of energy? • What energy conversion takes place as an object falls toward Earth?

15. 2 Energy Conversion and Conservation The movement of a meteor represents what type of energy? kinetic Some of this kinetic energy is converted into heat and light, thermal or ________ and radiant __________ energy

15. 2 Energy Conversion and Conservation Upon impact, much of the meteor's remaining kinetic energy went into crushing _________ the rear of this car in Peekskill, New York. Energy can be converted from one form to another!

15. 2 Energy Conversion and Conservation Energy Conversion The process of changing energy from one form to conversion another is energy ________. The striking of a match is a good example. chemical • Muscles use ________ energy to move the match. • Friction between the match and the matchbox converts kinetic thermal energy into _______ energy.

15. 2 Energy Conversion and Conservation Energy Conversion The thermal energy triggers a chemical reaction on the match tip, releasing some of the match’s ____ stored chemical energy This stored chemical energy is converted into _______ and thermal _________ radiant energy in the flame

15. 2 Energy Conversion and Conservation of Energy The law of conservation of energy states that cannot energy _______ be created or destroyed. form It can only change ______

15. 2 Energy Conversion and Conservation of Energy For example, the work down by friction changes _______ energy into _______ kinetic thermal energy Rub your hands against each other for a few seconds…what do you feel? Heat! Recall that friction within machinery ______ reduces efficiency

15. 2 Energy Conversion and Conservation of Energy Even these skaters are subject to friction…they are slowed down by friction with the _____ and the ________ of surface air the ice.

15. 2 Energy Conversion and Conservation Energy Conversions Gravitational potential energy As an object falls, its _______ gravitational _______ potential energy is converted to the kinetic ______ energy of motion. . Kinetic energy

15. 2 Energy Conversion and Conservation Energy Conversions One of the most common energy conversions is between potential energy and kinetic energy. • Example: A coiled spring has ______ potential energy elastic when it is compressed • When the spring expands, it is converted into kinetic _______ energy

15. 2 Energy Conversion and Conservation Energy Conversions Some gulls use energy conversion to obtain food _______while dropping oysters onto rocks. crack The kinetic energy causes the shell to _____ on collision with the rock.

15. 2 Energy Conversion and Conservation Energy Conversions A pendulum consists of a weight _______ back and forth swinging from a rope or a string Pendulum clocks use pendulums to maintain _______ time. accurate The time it takes for a pendulum to swing back and forth once is precisely related to its _____. length

15. 2 Energy Conversion and Conservation Energy Conversions Where does the pendulum have the greatest potential energy? Highest point of swing Where does the pendulum have the greatest kinetic energy? Bottom of swing

15. 2 Energy Conversion and Conservation Energy Conversions Energy Conversion and the Pole Vault In the pole vault, an athlete uses a flexible pole to propel himself over a high bar. As the pole bends, some of the kinetic energy is converted into elastic ____________ energy potential

15. 2 Energy Conversion and Conservation Energy Conversions The pole springs back into shape, propelling the pole-vaulter ________. upward • As the pole-vaulter rises, his decreases kinetic energy _______ while he _____ gravitational gains potential energy. • What type of energy does the pole-vaulter have at his highest point? Gravitational p. e.

15. 2 Energy Conversion and Conservation Energy Conversions As he falls, what type of energy does he have? Kinetic energy

15. 2 Energy Conversion and Conservation Energy Conversions Energy Conversion Calculations total Recall that mechanical energy is the _____ kinetic and potential energy of an object Mechanical energy = KE + PE When friction is small enough to be ______, ignored no and ______ mechanical energy is added to a system, then the system’s mechanical energy does ______ change. NOT

15. 2 Energy Conversion and Conservation Energy Conversions The law of conservation of energy applies to any mechanical process. If friction can be neglected, the total mechanical constant energy remains ________.

15. 2 Energy Conversion and Conservation Energy Conversions Conservation of Mechanical Energy 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. Mass = 1. 50 kg Speed = 26. 0 m/s Is the brick initially moving? no = PE = 1/2 (1. 50 kg) (26. 0 m/s)2 = 507 J

15. 2 Energy Conversion and Conservation Energy Conversions A pendulum with a 1. 0 -kg weight is set in motion from a position 0. 04 m above the lowest point on the path of the weight. What is the kinetic energy of the pendulum at the lowest point? (Hint: Assume there is no friction. ) Mass = 1. 0 kg Height = 0. 04 m (PE)beginning = mgh = (KE) (1. 0 kg)(9. 8 m/s 2)(0. 04 m) = KE 0. 4 J = KE

15. 2 Energy Conversion and Conservation Energy and Mass Einstein’s equation, E = mc 2, says that energy and mass are ________ and equivalent converted can be ______ into each other.

15. 2 Energy Conversion and Conservation Energy and Mass Albert Einstein developed his special theory of _________ in 1905. This theory included relativity the now-famous equation E = mc 2. energy • E is ________ mass • m is _______ • c is the ____________ = 3. 0 × 108 m/s speed of light A _____ amount of matter can produce small an _______ amount of energy. enormous

15. 2 Energy Conversion and Conservation Assessment Questions 1. What energy conversion occurs as a result of friction? (think of rubbing your hands) a. b. c. d. chemical energy to thermal energy kinetic energy to potential energy kinetic energy to thermal energy potential energy to thermal energy

15. 2 Energy Conversion and Conservation Assessment Questions 2. At what point in a pendulum’s swing does it have maximum kinetic energy? a. b. c. d. the highest point of the swing the lowest point of the swing halfway between the lowest and highest point same at all positions of the swing

15. 2 Energy Conversion and Conservation Assessment Questions 3. According to the law of conservation of mass, energy can be converted from one from to another but not created or destroyed. True False