Law of Conservation of Energy Pg. 236-241
Types of Energy We use mechanical energy (a combination of kinetic energy and gravitational potential energy) to do mechanical work every day But mechanical energy is not the only type of energy There are many types of energy in the universe, all of which involve kinetic energy, potential energy, or both
Types of Energy Electrical energy delivered to the stove heats the water in the pot Thermal energy in the boiling water transfers to the pasta to cook it
Types of Energy The sun emits radiant energies, such as infrared radiation, visible light, and ultraviolet radiation The sun s energy comes from nuclear fusion reactions in its core
Types of Energy At the highest position above the trampoline, this athlete has the greatest amount of gravitational potential energy This energy changes to kinetic energy as her downward velocity increases The kinetic energy then changes into elastic potential energy in the trampoline to help her bounce back up
Types of Energy Chemical potential energy is released when fireworks explode Some of that energy is changed into sound energy.
Types of Energy Notice that heat is not listed as a form of energy Heat is the transfer thermal energy from a warmer body or region to a cooler one ** in science, we use the word heat as a verb, not a noun. For example, the hot plate was used to heat the liquid to a temperature of 50 degrees celcius and not, the hot water has more heat than the cold water
Types of Energy ***make sure you have the chart from the text copied into your notes!!! (question from the worksheet)
Practice 1. Name at least one form of energy associated with each object in bold a) a bonfire roasts a marshmallow b) a baseball smashes a window c) a solar collector heats water for a swimming pool d) a stretched rubber band is used to launch a projectile e) the siren of an ambulance warns of an emergency a) chemical, radiant b) sound, kinetic c) radiant, nuclear d) elastic, kinetic e) sound, electrical
Energy Transformations The conversion of energy from one form to another is called an energy transformation For example, in a microwave oven, electrical energy transforms into radiant energy (microwaves), which is then transformed into thermal energy in the food being cooked Electrical energy Radiant energy Thermal energy
Energy Transformations People often wonder how much energy there is in the universe and whether we will eventually run out of energy Scientists have studied energy and energy transformations and have arrived at some important generalizations For example, they noticed that when one form of energy is transformed into another form (or forms) of energy, the quantity of one form is reduced by the same amount that the quantity of the other form (or forms) is increased For examples, a light bulb may transform 100 J of electrical energy into 5 J of radiant energy and 95 J of thermal energy However, the total amount of energy has not been changed
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Consider a 65 kg diver, 10.0 m high on a diving platform.
Law of Conservation of Energy
Practice 1. A ball is dropped vertically from a height of 1.5 m; it bounces back to a height of 1.3 m. Does this violate the law of conservation of energy? Explain. 2. A 56 kg diver jumps off the end of a 7.5 m platform with an initial horizontal speed of 3.6 m/s. a) determine the diver s total mechanical energy at the end of the platform relative to the surface of the water below b) apply the law of conservation of energy to determine the diver s speed at a height of 2.8 m above the water c) repeat (b) to find the maximum speed of the diver upon reaching the water a) E total @ start = 4500 J b) v = 10 m.s c) v = 13 m/s
3. A 0.20 kg ball is thrown straight up from the edge of a 30.0 m tall building at a velocity of 22.0 m/s. The ball moves up to the maximum height and then falls to the ground at the base of the building. Use the law of conservation of energy to answer the following questions, assuming that the reference level for gravitational potential energy is ground level. a) what is the total energy of the ball at the start when it had a velocity of 22.0 m/s? b) what is the velocity of the ball at the maximum height? c) what is the maximum height of the ball? d) what is the velocity of the ball when it hits the ground?
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Textbook Pg 241, #2 Discuss assignment : Rube-Goldberg Device