Pearson Prentice Hall Physical Science: Concepts in Action Chapter 15 Energy

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

How Energy & Work are Related + Kinetic Energy Def: energy is the ability to do work Work is a transfer of 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 for m are kg & v = (m/s)2 or m2/s2 the units for PE are kg*m2/s2 which is also called joules, J

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 Def: gravitational PE is PE that depends upon an object’s height Gravitational PE increases when an object is at a higher height

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, m When you multiply all the units together you get kg*9.8m/s2*m or kg*m2/s2 which is J 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

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?

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.

Forms of Energy The major forms of energy are mechanical energy, thermal energy, chemical energy, electrical energy, electromagnetic energy and nuclear energy Def: mechanical energy is the energy associated with the motion and position of everyday objects Def: thermal energy is the total PE and KE of all the microscopic particles in an object

Def: chemical energy is the energy stored in chemical bonds Def: electrical energy is the energy associated with electric charges Def: electromagnetic energy is a form of energy that travels through space in the form of waves Def: nuclear energy is the energy stored in atomic nuclei

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

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 Often energy converts directly from one form to another a wind up toy, for example, is PE to KE

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 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 Q: Where is the PE the greatest and KE zero?

Energy and Mass Mechanical energy = KE + PE Mechanical energy is also conserved (KE + PE)beginning = (KE + PE) end 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

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

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

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 Def: solar energy is sunlight converted to usable energy Solar energy is expensive and its use is limited until technology improves

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 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

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 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

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?