ENERGY AND POWER Chapter 13

The Nature of Energy Section I. What is Energy? - the ability to do work or cause change. Remember - Work is force over a distance. - or the transfer of energy.

II. Kinetic EnergyKinetic Energy (There are two general kinds of energy. - kinetic & potential) A. Kinetic Energy is the energy of motion. 1. Moving objects can do work & so they must have energy. 2. “Kinetos” - Greek for moving

(II. Kinetic Energy) B. Mass & Velocity - influence an object’s kinetic energy - ex. - think of a bowling ball & a golf ball Which would you need to exert more force on to move? Why?? Greater force = greater energy

III. Calculating Kinetic Energy A. Kinetic energy = mass x velocity what would have a greater affect on kinetic energy - doubling the mass or doubling the velocity?

List the order of the 3 vehicles by increasing K.E.

IV. Potential EnergyPotential Energy A. Energy that is stored and held in readiness. B. Two types of potential energy 1. Elastic 2. Gravitational

Elastic potential energy - P.E. that is associated with things can be stretched or compressed.

Gravitational Potential Energy Energy dependent on height GPA =

A rock posed for a fall has potential energy. How did it get its potential energy?

Different Forms Of EnergyForms Of Energy Some of the major forms of energy are: *Mechanical *Thermal *Chemical *Electrical *Electromagnetic *Nuclear

Mechanical Energy M.E. is associated with the motion or position of an object. M.E. can occur as kinetic or potential energy.

Mechanical Energy

What illustrates mechanical energy in this picture?

Thermal Energy -All matter is made up of particles. -These particles have both kinetic & potential energy - due to their arrangement & motion. - Thermal energy is the total energy of the particles in an object.

Thermal Energy When the thermal energy of an object increases, its particles move faster, making it feel warmer.

Chemical Energy Chemical energy is potential energy stored in chemical bonds that hold chemical compounds together. - stored in - foods - matches -cells of your body

Chemical Energy Food is chemical energy that is converted to mechanical energy.

Electrical Energy Moving electric charges produce electricity and the energy they carry is electrical energy. -Sources: - Power lines, batteries - lightning, static electricity

Electrical energy

Electromagnetic Energy E.M.E. energy travels in waves. These waves have some electrical properties and some magnetic.

Electromagnetic CT scan

Light is E.M.E.

Laser light is E.M.E.

NuclearNuclear Energy Nuclear energy is stored in the nucleus of an atom and is released during nuclear reactions These reactions release a tremendous amount of energy

2 Types of nuclear reactions: Nuclear Fission = when a nucleus splits Example: nuclear power plants use fission to produce electricity

Nuclear Fusion = when a nuclei fuse (join together) Occurs in the sun and other stars

The birth of a star - nuclear fusion takes place in stars.

Energy Conversion & Conservation Niagara Falls generates electricity.

Conversions Between Forms of Energy Energy Conversion = a change from one form of energy to another –Also referred to as “energy transformation” Most forms of energy can be converted into any other form

Energy Conversions - Electrical to electromagnetic.

Energy Conversions - Chemical to thermal.

Energy Conversions - Chemical to mechanical.

Kinetic and Potential Energy Most common conversion is potential to kinetic energy. –Ex: Stretching a rubber band gives it elastic potential energy. When the rubber band is moving, it has kinetic energy. The potential energy of the stretched rubber band is converted to the kinetic energy of the moving rubber band.

Energy conversions enable this athlete to vault into the air. What conversions are taking place?

Energy Conversion Juggling: –Any object that rises or falls experiences a change in its kinetic & gravitation potential energy.

At what point(s) does K.E. = to zero?

Energy Conversions Waterfall: –The water at the top of the falls has gravitational potential energy (because it is higher than the bottom of the falls). –But as the water falls, its height decreases, so it loses potential energy. –At the same time its kinetic energy increases because its velocity increases. –So, the P.E. is converted into K.E.

What is wrong with this picture?

Energy Conversions Pole Vault: –As a pole vaulter runs, he has K.E because he is moving. –His K.E is converted to E.P.E as his pole bends and absorbs energy. –As the pole straightens, E.P.E is converted to G.P.E as the vaulter is lifted into the air. –G.P.E is converted to K.E as the vaulter clears the bar and falls to the mat.

Energy Conversions Pendulum: –A continuous conversion of K.E and P.E takes place in a pendulum.

(Gravitational)

Conservation of Energy Law of Conservation of Energy states that energy cannot be created or destroyed. When one form of energy is converted to another, no energy is destroyed in the process.

Conservation of Energy Question: –If you set a pendulum in motion, does it remain in motion forever? No, it will not. All energy can be accounted for. So, where did it go? Converted to other forms

Energy and Friction So, what happens to the K.E of the pendulum? When object’s experience friction, the motion (the K.E) of the atoms or molecules increases  thermal energy increases! So, mechanical energy of the moving pendulum is converted to thermal energy. The pendulum slows down but its energy is not destroyed!

Now, can you explain why no machine is 100% efficient? In a machine, work output is always less than work input because the energy “wasted” on friction is converted to thermal energy in a machine.

Energy & Matter In nuclear reactions, where huge amounts of energy are produced by destroying tiny amounts of matter. Energy alone is not conserved but matter & energy together are conserved! Remember: E = mc 2

Conserving Energy Conserving energy means saving energy, or not wasting it. Don’t confuse this with the Law of Conservation of Energy which refers to a quantity that remains constant. Remember, in science, energy is always conserved because its total quantity does not change.

Sec 3: Energy Conversions & Fossil Fuels Fossil Fuels contain energy that came from the sun. –Coal, Petroleum, & natural gas Created millions of years ago from ancient plants & animals.

This ancient forest was part of the Carboniferous Period.

Use of Fossil Fuels Fossil fuels can be burned to release the potential chemical energy stored millions of years ago. (Rich in carbon compounds) Process of burning fuel = combustion.

Coal - a FOSSIL fuel. The carbon remains of plants deposited during the Carboniferous Period.

Exploring Energy Conversions

Ancient plants and animals convert electromagnetic energy from the sun into stored chemical energy.

The remains of plants & animals become coal over millions of years.

Stored chemical energy in coal is converted to thermal energy to make steam. Thermal energy is converted to mechanical energy as the steam turns turbines. Mechanical energy is converted into electrical energy as the moving turbines generate electricity.

Electrical energy is converted to thermal energy in a toaster.

Sec 4: Power Power is the rate at which work is done or the amount of work done in a unit of time. Power = Work / Time Power = (Force x Distance) / Time

Work is measured in joules, time in seconds, the unit of power is the joule. So, the unit for power is Joule/second (J/s). J/s is also called the watt (W). 1 watt = 1 J/s 1kW = 1,000 watts –Washing machines use about 1kW when its running.

Power & Energy Recall that work is the transfer of energy. So, power can be considered the rate at which energy is transferred from one object to another or converted to one form to another. For this reason, power is not limited to situations in which objects are moved. Power can be found whenever energy is being transferred or converted.

Example: Comparing Light Bulbs 100 W light bulb is much brighter than a 40 W light bulb. A 100 W light bulb converts electrical energy at a rate of 100 J each second A 100 W bulb is brighter because it gives off more energy per second than a 40 W.

Horsepower James Watt used the term “horsepower” to advertise the advantages of his steam engine. –He defined 1 horsepower as the amount of work a horse does to lift a 33,000-pound weight a distance of 1 foot in 1 minute.

One horsepower = 746 watts. This is not an SI unit.

THE END