Can energy be converted 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?

The movement of a meteor represents what type of energy? Some of this kinetic energy is converted into heat and light, or _______________ and ___________________ energy kinetic thermal radiant

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

The striking of a match is a good example. Energy Conversion The process of changing energy from one form to another is energy ________________. conversion The striking of a match is a good example. Muscles use _______________ energy to move the match. Friction between the match and the matchbox converts kinetic energy into _____________ energy. chemical thermal

Energy Conversion The thermal energy triggers a chemical reaction on the match tip, releasing some of the match’s ________ chemical energy This stored chemical energy is converted into ______________ and __________________ energy in the flame stored thermal radiant

Conservation of Energy The law of conservation of energy states that energy ______________ be created or destroyed. It can only change ____________ cannot form

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

Conservation of Energy Even these skaters are subject to friction…they are slowed down by friction with the _________ and the _______________ of the ice. air surface

Energy Conversions Gravitational potential energy As an object falls, its _____________ _____________ energy is converted to the ____________ energy of motion. . gravitational potential kinetic Kinetic energy

Energy Conversions One of the most common energy conversions is between potential energy and kinetic energy. Example: A coiled spring has ____________ potential energy when it is compressed When the spring expands, it is converted into ______________ energy elastic kinetic

Energy Conversions Some gulls use energy conversion to obtain _______while dropping oysters onto rocks. The kinetic energy causes the shell to __________ on collision with the rock. food crack

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

Where does the pendulum have the greatest potential energy? Energy Conversions Where does the pendulum have the greatest potential energy? Where does the pendulum have the greatest kinetic energy? Highest point of swing Bottom of swing

Energy Conversion and the Pole Vault 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 ____________ ____________ energy elastic potential

Energy Conversions The pole springs back into shape, propelling the pole-vaulter _______________. As the pole-vaulter rises, his kinetic energy ______________ while he _________ gravitational potential energy. What type of energy does the pole-vaulter have at his highest point? upward decreases gains Gravitational p. e.

Energy Conversions As he falls, what type of energy does he have? Kinetic energy

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

The law of conservation of energy applies to any mechanical process. Energy Conversions The law of conservation of energy applies to any mechanical process. If friction can be neglected, the total mechanical energy remains _______________. constant

Conservation of Mechanical Energy 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 = Speed = Is the brick initially moving? 1.50 kg = 26.0 m/s PE = 1/2 (1.50 kg) (26.0 m/s)2 no = 507 J

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 = Height = 1.0 kg (PE)beginning = mgh = (KE) 0.04 m (1.0 kg) (9.8 m/s2) (0.04m) = KE 0.4 J = KE

Energy and Mass Einstein’s equation, E = mc2, says that energy and mass are ________________ and can be ____________ into each other. equivalent converted

A __________ amount of matter can produce Energy and Mass Albert Einstein developed his special theory of __________________ in 1905. This theory included the now-famous equation E = mc2. E is _______________ m is _____________ c is the ________________________ = 3.0 × 108 m/s A __________ amount of matter can produce an _____________ amount of energy. relativity energy mass speed of light small enormous

Assessment Questions What energy conversion occurs as a result of friction? (think of rubbing your hands) chemical energy to thermal energy kinetic energy to potential energy kinetic energy to thermal energy potential energy to thermal energy

Assessment Questions At what point in a pendulum’s swing does it have maximum kinetic energy? 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

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