Presentation on theme: "Pearson Prentice Hall Physical Science: Concepts in Action"— Presentation transcript:
1 Pearson Prentice Hall Physical Science: Concepts in Action Chapter 15Energy
2 15.1 Energy and Its Forms Objectives: 1. Describe and compare how energy and work are related2. Explain what factors kinetic energy of an object depends on3. Discuss how gravitational potential energy is determined4. Summarize the major forms of energy
3 How Energy & Work are Related + Kinetic Energy Def: energy is the ability to do workWork is a transfer of energyDef: kinetic energy is the energy of motionThe kinetic energy of any moving object depends on its mass and speedThe formula is: KE = ½ mv2 where m = mass and v is the velocity (which must be squared)the units for m are kg & v = (m/s)2 or m2/s2the units for PE are kg*m2/s2 which is also called joules, J
4 Potential EnergyDef: potential energy is stored energy as a result of position or shapePE is energy with the potential to do workTwo forms of PE are gravitational PE and elastic PEDef: gravitational PE is PE that depends upon an object’s heightGravitational PE increases when an object is at a higher height
5 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, mWhen you multiply all the units together you get kg*9.8m/s2*m or kg*m2/s2 which is JDef: elastic PE is the PE of an object that is stretched or compressedAn object is elastic if it springs back after being stretched
6 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?
7 Practice ProblemsCalculate 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.
8 Forms of EnergyThe major forms of energy are mechanical energy, thermal energy, chemical energy, electrical energy, electromagnetic energy and nuclear energyDef: mechanical energy is the energy associated with the motion and position of everyday objectsDef: thermal energy is the total PE and KE of all the microscopic particles in an object
9 Def: chemical energy is the energy stored in chemical bonds Def: electrical energy is the energy associated with electric chargesDef: electromagnetic energy is a form of energy that travels through space in the form of wavesDef: nuclear energy is the energy stored in atomic nuclei
10 15.2 Energy Conversion & Conservation Objectives:1. Describe how energy can be converted from one form to another2. Explain the law of conservation of energy3. Discuss the energy conversion that takes place as an object falls toward Earth4. Discuss how energy and mass are related
11 Energy Can be Converted from One Form to Another Def: energy conversion is the process of changing energy from one form to anotherSometimes energy is converted to other forms in a series of stepsEx: 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 energyOften energy converts directly from one form to anothera wind up toy, for example, is PE to KE
12 Conservation of Energy + Energy Conversions and Gravity The Law of Conservation of Energy states that energy cannot be created or destroyedThe gravitational PE of an object is converted to the KE of motion as an object fallsPendulums constantly convert PE to KE and KE to PE as the pendulum swingsAt the bottom of the swing, the pendulum has maximum KE and zero PEOn either side the pendulum will have a combination of PE + KEQ: Where is the PE the greatest and KE zero?
13 Energy and Mass Mechanical energy = KE + PE Mechanical energy is also conserved(KE + PE)beginning = (KE + PE) endEinstein 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)2This equation says that energy and mass are equivalent and can be converted into each otherIt also means that a tiny amount of matter can produce enormous amounts of energyMass and energy together are always conserved
14 2. Explain how energy resources can be conserved Objectives:1. Give examples of the major nonrenewable and renewable energy sources2. Explain how energy resources can be conserved
15 Nonrenewable and Renewable Nonrenewable energy resources include oil, natural gas, coal and uraniumOil, natural gas and coal are fossil fuelsFossil fuels were formed underground from once living organismsMost nonrenewable resources are considered inexpensive, available and are known to cause pollution
16 Renewable energy resources include hydroelectric, solar, geothermal, wind, and biomass Def: hydroelectric energy is energy obtained from flowing waterHydroelectric energy production usually involves the building of a damHydroelectric is available, used today and generally nonpollutingDef: solar energy is sunlight converted to usable energySolar energy is expensive and its use is limited until technology improves
17 Def: geothermal energy is thermal energy beneath the earth’s surface It is nonpolluting and available in this area due to naturally occurring hot springsmost places are not near a volcano or hot springsDef: biomass energy is the energy stored in living thingsBiomass can be converted directly to thermal energyAgricultural waste such as turning corn into ethanol for auto fuel is an exampleThis technology is moderately expensive
18 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 continuesHydrogen fuel cells are being used in some places to generate electricity by reacting hydrogen with oxygenThe main source of hydrogen is waterThis technology is expensive and considered to be a research and development project for future energy sources
19 Conservation of Resources Energy resources can be conserved by reducing energy needs and by increasing the efficiency of energy useDef: energy conservation is finding ways to use less energy or use energy more efficientlyQ: Can you think of some ways we can conserve energy resources?