Work and Energy,Structure of Matter

Basic Concepts

Work and EnergyEnergy and work are closely related terms.They are both abbreviated the same way

(W) but are defined and used in a different way

Work is used to perform some task.When a car engine starts, energy from the

battery is used to do the work of cranking the engine.

The work done and energy used are two ways of saying the same thing.

Work and EnergyWork is defined as a force moving through

a distance.Energy is the ability, or capacity, to do

work.Remember...

Energy is independent of work; it exists whether or not work is being done.

Work requires energy.

Units of EnergyBase units are terms used to indicate the amount of

something.The joule is the base unit of energy and work.

The symbol used for the joule is J.Specifying base units are important because nearly

all relationships in electricity are expressed this way.

A joule of energy (or work) is very small compared to the amount of energy you use each day.Toaster used 100,000 joules to toast two slices of

bread.360,000 joules are required to light a lamp for an hour.

Here comes some math!Work or energy in a mechanical system can

be determined by the following relationship:

The base unit for force is the newton and the base unit for distance is the meter.

The joule is equal to the newton-meter.

Example 1If it requires a steady force of 150 newtons to pull

a boat, how much work is required to pull a boat 8 meters?

Given: Force = 150 newtons, Distance = 8 metersFind: WorkKnown: 1 newton-meter = 1 joule (J)Solution: Work = 150 newtons * 8 meters Work = 1200 newton-meters Work = 1200 joules W = 1200 J

Example 2It requires 500 joules of energy and 100 newtons of

force to move an object from point A to point B. What is the distance between point A and point B

Given: Energy = 500 joules, Force = 100 newtonsFind: DistanceKnown: Distance = W/ForceSolution: Distance = 500 newton-meters / 100

newtons =5 meters

Answer: Distance = 5 meters

Energy ConversionOne of the fundamental laws of

physics states that, under ordinary conditions, energy can neither be created or destroyed.

Various forms of energy include:HeatLightElectricChemicalMechanical

When we “use” energy, we convert it.

EfficiencyEnergy conversion is never 100%

successful. In other words, not all the energy meant to be converted is released in the form of energy desired.

In a light bulb, 1000 joules of electric energy is put into a light bulb and only 200 joules of light are produced. What happens to the other 800 joules?

Efficiency of a system is expressed as a percentage and calculated with the following equation:

Efficiency ExampleWhat is the efficiency of a light bulb that uses

1000 joules of electric energy to produce 200 joules of light energy?

Find: Percent efficiencyKnown: % eff. = (Wout / Win) * 100Solution: % eff. = (200 joules / 1000 joules) * 100 = 0.2 * 100

= 20Answer: Efficiency = 20%

Structure of MatterAll matter is composed of atoms, the basic

building blocks of nature.The smallest particle of a substance that still

has all of its characteristics is called a molecule. A molecules consists of two or more atoms.

Matter composed of a single type of atom is called an element.

When different kinds of atoms combine chemically, they form materials called compounds.

The AtomBe sure to know

the difference between:ElectronProtonNeutronNucleusShellOrbitIonsValence electrons

Electric Charge Both electrons and protons possess electric

charges, but these charges are of opposite polarity. Polarity refers to the type (negative or positive) of

charge.Proton = Positive (+)Electron = (-)Neutron = No Charge

The electrons in the outermost shell of an atom are called valence electrons and are involved in chemical reactions and electric current.

All electrons posses energy because they have weight and they are moving, thus they are capable of doing work.

Valence electrons posses more energy than electrons in the inner shells.