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Pearson Prentice Hall Physical Science: Concepts in Action
Chapter 15 Energy Bill Nye Energy
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15.1 Energy and Its Forms Objectives:
1. Describe and compare how energy and work are related 2. Explain what factors kinetic energy of an object depends on 3. Discuss how gravitational potential energy is determined 4. Summarize the major forms of energy
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How Energy & Work are Related + Kinetic Energy
Def: energy is the ability to do work Work is a transfer of energy
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Work = Force x Displacement
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Work = Force x Displacement
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How Energy & Work are Related + Kinetic Energy
Def: kinetic energy is the energy of motion The kinetic energy of any moving object depends on its mass and speed The formula is: KE = ½ mv2 where m = mass and v is the velocity (which must be squared) The units are kg*m2/s2 which is also called joules, J
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Practice Problems Calculate the KE of a 1500kg car moving at 29m/s.
A bowling ball traveling at 2.0m/s has 16J of KE. What is the mass of the bowling ball in kg?
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Potential Energy Def: potential energy is stored energy as a result of position or shape PE is energy with the potential to do work Two forms of PE are gravitational PE and elastic PE
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Potential Energy Def: gravitational PE is PE that depends upon an object’s height Gravitational PE increases when an object is at a higher height
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Work and Energy conversions
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Phet
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An object’s gravitational PE depends on its mass, height & acceleration due to gravity
The formula for gravitational PE = mgh where m= mass (kg), g= 9.8 m/s2 (the free fall acceleration of gravity) & h = height in meters When you multiply all the units together you get kg*9.8m/s2*m or kg*m2/s2 which is J
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Practice Problems Calculate the PE of a car with a mass of 1200kg at the top of a 42m hill. Calculate the PE of a 55g egg held out of a 2nd story window, 6m off the ground.
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Elastic Potential Energy
Def: elastic PE is the PE of an object that is stretched or compressed An object is elastic if it springs back after being stretched
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Forms of Energy The major forms of energy are mechanical energy, thermal energy, chemical energy, electrical energy, electromagnetic energy and nuclear energy
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Forms of Energy Def: mechanical energy is the energy associated with the motion and position of everyday objects
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Def: thermal energy is the total PE and KE of all the microscopic particles in an object
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Def: chemical energy is the energy stored in chemical bonds
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Def: electrical energy is the energy associated with electric charges
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Def: electromagnetic energy is a form of energy that travels through space in the form of waves
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Def: nuclear energy is the energy stored in atomic nuclei
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15.2 Energy Conversion & Conservation
Objectives: 1. Describe how energy can be converted from one form to another 2. Explain the law of conservation of energy 3. Discuss the energy conversion that takes place as an object falls toward Earth 4. Discuss how energy and mass are related
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Energy Can be Converted from One Form to Another
Our modern world is shaped by energy conversions Solar Panels Wind Turbines Lights …
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Energy Can be Converted from One Form to Another
Def: energy conversion is the process of changing energy from one form to another Sometimes energy is converted to other forms in a series of steps Ex: striking a match uses chemical energy from your muscles, then friction between match and box converts KE to thermal energy, thermal energy triggers a chemical reaction releasing more chemical energy
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Turbine in an electric generator
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Energy Can be Converted from One Form to Another
Often energy converts directly from one form to another a wind up toy, for example, is PE to KE
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Conservation of Energy + Energy Conversions and Gravity
The Law of Conservation of Energy states that energy cannot be created or destroyed The gravitational PE of an object is converted to the KE of motion as an object falls
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Conservation of Energy + Energy Conversions and Gravity
Pendulums constantly convert PE to KE and KE to PE as the pendulum swings At the bottom of the swing, the pendulum has maximum KE and zero PE On either side the pendulum will have a combination of PE + KE
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Big Ben The Big Ben uses potential energy from the pendulum kinetic energy of the swing to turns gears and time the clock
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A continuous exchange between EK and EP occurs.
At the bottom of the swing, the pendulum has maximum KE and zero PE Q: Where is the PE the greatest and KE zero? © 2015 By Timothy K. Lund
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Energy and Mass Mechanical energy = KE + PE
Mechanical energy is also conserved (KE + PE)beginning = (KE + PE) end
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Energy and Mass Einstein has an equation: E = mc2 where E is energy (J), m is mass (kg) & c2 is the speed of light squared (3 x 108 m/s)2 This equation says that energy and mass are equivalent and can be converted into each other It also means that a tiny amount of matter can produce enormous amounts of energy Mass and energy together are always conserved
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E = mc2 and Mass defect
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PE KE Conversions – Math Example
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2. Explain how energy resources can be conserved
Objectives: 1. Give examples of the major nonrenewable and renewable energy sources 2. Explain how energy resources can be conserved
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Nonrenewable and Renewable
Nonrenewable energy resources include oil, natural gas, coal and uranium Oil, natural gas and coal are fossil fuels Fossil fuels were formed underground from once living organisms Most nonrenewable resources are considered inexpensive, available and are known to cause pollution
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Renewable energy resources include hydroelectric, solar, geothermal, wind, and biomass
Def: hydroelectric energy is energy obtained from flowing water Hydroelectric energy production usually involves the building of a dam Hydroelectric is available, used today and generally nonpolluting
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Def: solar energy is sunlight converted to usable energy
Solar energy is expensive and its use is limited until technology improves
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Def: geothermal energy is thermal energy beneath the earth’s surface
It is nonpolluting and available in this area due to naturally occurring hot springs most places are not near a volcano or hot springs
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Def: biomass energy is the energy stored in living things
Biomass can be converted directly to thermal energy Agricultural waste such as turning corn into ethanol for auto fuel is an example This technology is moderately expensive
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Wind energy requires a lot of land and a place that has a lot of wind
It is expensive and not practical at this time although research continues
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Hydrogen fuel cells are being used in some places to generate electricity by reacting hydrogen with oxygen The main source of hydrogen is water This technology is expensive and considered to be a research and development project for future energy sources
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Conservation of Resources
Energy resources can be conserved by reducing energy needs and by increasing the efficiency of energy use Def: energy conservation is finding ways to use less energy or use energy more efficiently Q: Can you think of some ways we can conserve energy resources?
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