# Energy – Chapter 9 The Nature of Energy.

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Energy – Chapter 9 The Nature of Energy

2-Column Notes MAIN IDEA DETAILS What is Energy?
The ability to do work or cause change Work is the transfer of energy What is Kinetic Energy? Two kinds of energy are POTENTIAL and KINETIC Kinetic is energy of motion Kinetic comes from the Greek word ‘Kinetos’ which means ‘Moving’

Kinetic Energy - Motion
Kinetic comes from the Greek word kinetos meaning ‘moving’.

2-Column Notes MAIN IDEA DETAILS
How is Mass and Velocity Related to Kinetic Energy? Kinetic energy depends upon both mass and velocity More mass requires less velocity to have same energy Kinetic energy increases as mass increases Kinetic energy increases as velocity increases

2-Column Notes MAIN IDEA DETAILS How do we calculate Kinetic Energy?
EK = (Mass x Velocity2 )/2

Energy MAIN IDEA DETAILS What is Potential Energy?
Potential energy is energy that is stored. It has the potential to do work Energy that has to do with stretching or compressing objects is elastic potential energy Energy that has to do with height is gravitational potential energy

Calculating Potential Energy
Gravitational Potential Energy = Weight X Height Weight IS NOT Mass Weight = Mass X Gravitational Acceleration SI Unit of measure for weight is ‘newton’. One ‘newton’ is the force required to accelerate on kg 1 m/s/s Gravitational Acceleration = 9.8 m/s/s Energy is measured in ‘joules’ = ‘newton-meter’

Energy MAIN IDEA DETAILS (Continued) Gravitational Potential Energy =
Weight x Height Energy is measured in joules Weight = Mass x Gravitational Acceleration Therefore: EGP=Mass x Gravity x Height

Energy MAIN IDEA DETAILS What are the different forms of Energy?
Mechanical: motion or position of an object Thermal: Total energy in the particles of an object Chemical: Energy stored in chemical bonds Electrical: energy in moving electrons Electromagnetic: energy traveling in waves (light, sound) Nuclear: energy stored in nucleus of an atom

Kinetic Energy - Motion
Kinetic comes from the Greek word kinetos meaning ‘moving’.

Potential Energy – Stored & Waiting
The rock has potential to do work, or to move. This is ‘gravitational’ potential energy. Elastic potential energy is associated with objects that can stretch or be compressed (springs). Stored energy has the ‘Potential’ to do work

Mechanical Energy Mechanical Energy is the energy associated with the motion or position of an object.

Thermal Energy - Heat The faster the molecules and electrons move, the more thermal energy it contains. All Atoms and Molecules are particles in motion. The faster they move, the more Thermal energy they have. The more thermal energy, the ‘hotter’ they are.

Chemical Energy – Energy Stored in Chemical Bonds
Chemical reactions give off or take in energy to create the chemical bonds. The energy stored in the chemical bonds is Chemical Energy and can be released by breaking the bonds

Electrical Energy Electrical Energy is the energy associated with moving electrical charges.

Electromagnetic Energy - Light
Electromagnetic energy is energy traveling in waves. This includes light and sound.

Nuclear Energy Nuclear Energy is the energy that holds the nucleus of an atom together. ‘Splitting’ the nucleus is an atomic reaction that releases tremendous potential energy.

Review Questions Are energy and work the same thing?
No: Energy is the potential to do work. Work is done when energy is transferred from one object to another How are kinetic and potential energy different? Kinetic is the energy of motion. Potential is stored energy.

Review Questions - 2 List the forms of energy and give an example of each: Mechanical Car moving Thermal: Warm water Chemical Gasoline Electrical Battery Electromagnetic Light Nuclear Sun

Review Questions - 3 A boulder weighs 200N, poised at the edge of a 100M cliff. What is its gravitational potential energy? Draw a graph of its potential energy as it falls from 100M to 50M to 20M to 10M EGP=200N x 100M = 20,000J At 50 M, = 200N x 50M = 10,000J At 20 M, = 200N x 20M = 4000J At 10 M, = 200N x 10M = 2000J

Exercise – calculate your potential energy
One Kg is 2.2 pounds at sea level. Your mass is your weight divided by 2.2 Assume you are 1 meter above the floor, about the height of the desk. The gravitational acceleration constant is 9.8 m/s/s

Energy Conversion and Conservation

Energy Conversion and Conservation
MAIN IDEA DETAILS How do conversions between forms of energy occur? Change from one form of energy to another is an energy conversion Any form of energy can be converted to any other form

Energy Conversion & Conservation
MAIN IDEA DETAILS How Does Kinetic and Potential Energy Convert? Potential to Kinetic and vice versa is most common conversion. What is the energy conversion in juggling? Object rising or falling is changing kinetic energy to/from Gravitational Potential Energy What is the energy conversion in a Waterfall: At top of waterfall, water has potential energy. As it falls it is converted to kinetic energy.

Energy Conversion and Conservation
MAIN IDEA DETAILS What is the energy conversion in a Pole Vault? Pole vaulter runs (kinetic). Plants pole which bends (elastic). Vaulter springs into the air (kinetic) which changes to height (gravitational potential). Vaulter falls (kinetic) What is the energy conversion in a pendulum? Continuous conversion between gravitational potential and kinetic. As it goes up, kinetic is converted to potential. Going down, converted from potential to kinetic

Energy Conversion & Conservation
MAIN IDEA DETAILS What is the law of conservation of energy? Energy cannot be created or destroyed, but can be transformed to any other type of energy OR- When one form of energy is converted to another, no energy is destroyed in the process

Energy Conversion & Conservation
MAIN IDEA DETAILS What is the relationship between energy and matter? Einstein: Energy can be created by destroying matter Nuclear reactions What is Conserving Energy? Not the same as conservation of energy Means saving or not wasting energy

Reality and Energy Conversions
No energy conversion is 100% efficient Some energy is always lost to the environment Usually as heat Power Generation through Energy Usage is a problem of efficiency Efficiency = \$\$\$\$ Heat is a form of pollution Global warming Kills fish in lakes that are too warm

Review Questions MAIN IDEA DETAILS What is an energy conversion?
A change from one form of energy to another form State the law of conservation of energy in your own words: The total energy before a process is the same as the total after the process.

Review Questions MAIN IDEA DETAILS
Describe the energy conversions that occur when a ball is dropped and bounces back up. Why do you think the ball bounces a little lower each time? Falling: potential changes to kinetic. Bouncing back up: kinetic changes back to potential Ball does not bounce as high because some energy escapes as thermal (friction) or sound

Energy Conversion & Conservation
MAIN IDEA DETAILS A roller coaster car with a mass of 500 Kg is at the top of the hill that is 30m high. Without friction, what would its kinetic energy be as it reached the bottom of the hill? Without friction, kinetic would equal gravitational potential: 500kg x 9.8 m/s2 x 30 m = 147,000J

Energy Conversions

Energy Conversion Energy transformation, energy transfer, energy conversion or power transfer, any process of transforming one form of energy into another. Energy of fossil fuels, solar radiation, or nuclear fuels can be converted into other energy forms such as electrical, propulsive, or heating that are more useful to people. Often, machines are used to transform energy. The efficiency of a machine characterizes how well (how efficiently) it can produce a useful output (such as work for example) through such a conversion.

Energy Conversion Coal Power Plants:
For instance, a coal-fired power plant involves these power transfers: Potential energy in the coal converted to thermal energy Thermal energy converted to kinetic energy in steam Steam energy converted to mechanical energy in the turbine Mechanical energy of the turbine converted to electrical energy, which is the ultimate output

Energy Conversions - Car
Potential energy in the fuel converted to kinetic energy of expanding gas via combustion Kinetic energy of expanding gas converted to linear piston movement Linear piston movement converted to rotary crankshaft movement Rotary crankshaft movement passed into transmission assembly Rotary movement passed out of transmission assembly in second step Rotary movement passed through differential Rotary movement passed out of differential to drive wheels Rotary movement of drive wheels converted to linear motion of the vehicle

Other Energy Conversions
Thermophotovoltaics (Heat → Electricity) Geothermal power (Heat → Electricity) Heat engines, such as the internal combustion engine used in cars, or the steam engine (Heat → Mechanical energy) Ocean thermal power (Heat → Electricity) Hydroelectric dams (Gravitational potential energy → Electricity) Electric generator (Kinetic energy or Mechanical work → Electricity) Fuel cells (Chemical energy → Electricity) Lamp (Chemical energy → Heat and Light) Microphone (Sound → Electricity) Nuclear reactor (Nuclear energy → Electricity) Fossil fuel power plant (Chemical energy → Electricity) Solar cells (Light → Electricity), including downconversion and upconversion Solar thermal (Light → Heat) Wave power (Mechanical energy → Electricity) Windmills (Wind energy → Electricity or Mechanical energy) Piezoelectrics (Strain → Electricity) Acoustoelectrics (Sound → Electricity)

Energy Conversion Efficiency
Energy efficiency Combustion engine 10-50%[1] Gas turbine up to 40% Gas & Steam Turbine Cooperation up to 60% Water Turbine up to 90% (practically achieved) Wind Turbine up to 59% (theoretical limit) Solar cell current maximum 42.8% (50% short term goal)[2] Firearm ~30% (.300 Hawk ammunition) Fuel Cell up to 80% Water Electrolysis 50%-70% (80%-94% theoretical maximum) Photosynthesis up to 6% Muscle 14% - 27% Electric motors 30-60% (small ones < 10W); (middle ones between W); % above 200W Household refrigerators low end systems ~ 20%; high end systems ~ 40-50% Incandescent bulbs 5-10% Light Emitting Diodes up to 35% [3] Fluorescent lamps 28% [4] Low pressure sodium lamps 40.5% [4] Metal halide lamps 24% [4] Electric shower 90-95% ( Overall it would be more efficient to use a heat pump, requiring less electric energy[citation needed]) Electric heaters exactly 100% (all energy is always converted into heat anyway)

Energy Conversion Efficiency
Electric motors 30-60% (small ones < 10W); (middle ones between W); % above 200W Household refrigerators low end systems ~ 20%; high end systems ~ 40-50% Incandescent bulbs 5-10% Light Emitting Diodes up to 35% [3] Fluorescent lamps 28% [4] Low pressure sodium lamps 40.5% [4] Metal halide lamps 24% [4] Electric shower 90-95% ( Overall it would be more efficient to use a heat pump, requiring less electric energy[citation needed]) Electric heaters exactly 100% (all energy is always converted into heat anyway)

Energy Conversion & Fossil Fuels
MAIN IDEA DETAILS How are Fossil Fuels Formed? Stored energy from hundreds of millions of years ago, formed by geologic processes Includes: coal, gas, petroleum Contain energy that came from the sun

Energy Conversion & Fossil Fuels
MAIN IDEA DETAILS How do we use fossil fuels? Burned to release the potential chemical energy Chemical changed to thermal (fire) to heat water Water (steam) turns turbines (mechanical) Turbine turns a generator to make electricity

Energy Conversion & Fossil Fuels
MAIN IDEA DETAILS How is the chemical energy in fossil fuels related to the sun’s energy? Fossil fuels are stored energy from the sun How is the energy of coal released? Combustion (burned) to release potential energy into thermal energy

Energy Conversion & Fossil Fuels
MAIN IDEA DETAILS Describe energy conversions involved in the formation of coal. Nuclear energy (sun) converted to electromagnetic (light) Light converted to chemical (Plants/animals) When exposed to high temperature and pressure over many years, it becomes coal.

Energy Conversion & Fossil Fuels
MAIN IDEA DETAILS Make a general statement about the supply of fossil fuels, given what you know about how fossil fuels are formed: Fossil fuels are formed much more slowly than we are using them, so supply may become increasingly scarce.