Work, Energy, and Power

Work (W)The product of the force (F) applied to an object over a distance (d) in which the object travels as a result of the force

W F d Joule (j) is the base unit of work

1 1 1joule newton meter

J N m

(Force and distance must be parallel to each other)

A student lifts a 50 pound (lb) ball 4 feet (ft) in 5 seconds (s).

How many joules of work has the student completed?

W F d 222.5 1.22W N m

271W J

1 4.45lb NConvert English units to SI units

1 0.305ft m

Solve for Work

Work Example

50.0 4.45 222.5 223 lb N N 4.00 0.305 1.22ft m

Energy

Ability to do work (light, heat, mechanical, chemical, electrical)

NASA solar sail Fuel cellRoller coaster

Forms of EnergyPotential Energy (Stored energy or gravitational energy)

The capacity to do work by virtue of position or configuration

Forms of EnergyKinetic Energy (Energy of motion)

Energy which a body possesses because of its motion, which occurs anywhere from an atomic level to that of a whole organism

Energy Transformation

Chemical

Radiant

Electrical

Renewable Energy SourcesBiomassBiomass HydropoweHydropower GeothermalGeothermal

WindWind SolarSolar

Nonrenewable Energy Sources

PetroleumPetroleum

Natural GasNatural GasCoalCoal

UraniumUranium

Conservation of EnergyEnergy cannot be created or destroyed, but it can change from one form to another.

Energy Efficiency: The ratio of the useful energy delivered by a dynamic system to the energy supplied to it

Entropy: The loss of energy during conversion

outputEfficiency% x100

input

Energy ConversionChanging one form of energy to another

Energy ConversionExamples

Fossil fuels Chemical → Heat → Mechanical → Electrical

Solar cells Sunlight → Electrical

Wind turbines Kinetic → Mechanical → Electrical

Hydroelectric Gravitational potential → Mechanical → Electrical

Nuclear Nuclear → Heat → Mechanical → Electrical

Vehicle System Conversion

Chemical

Mechanical HeatWhich output is desired, mechanical or heat?

What Are Current Energy Concerns?

ConsumptionConsumption

What roles do engineers have in energy?What roles do engineers have in energy?

PollutionPollutionDepletionDepletionDependencyDependencyCostCost

http://www.eia.doe.gov

PowerRate at which work is performed or energy is expended

WP=

tWatt is the base unit of Power

One watt is equal to 1 joule of work per second

Types of Power

Electrical Power

Uses electrical energy to do work

Mechanical Power

Uses mechanical energy to do work (linear, rotary)

Fluid Power

Uses energy transferred by liquids (hydraulic) and gases (pneumatic)

Power Example

Power = Work / Time

Work = 271.45J

P

P

271.45 J5.00s

J54.3

s

P

J1 1Watt( W)s

54.3W

A student lifts a 50.0 pound (lb) ball 4.00 feet (ft) in 5 .00seconds (s). How many watts of power are used to lift the ball?

Resources

McGraw-Hill dictionary of engineering. (2nd ed.). New York, NY: McGraw-Hill.

Microsoft, Inc. (2008). Clip art. Retrieved January 10, 2008, from http://office.microsoft.com/en-us/clipart/default.aspx

National Aeronautics and Space Administration (NASA). (1997). Daedalus. Retrieved April 2, 2008, from http://www.dfrc.nasa.gov/Gallery /Photo/Daedalus/

U.S. Department of Energy. (2008). Scientific forms of energy. Retrieved March 23, 2008, from http://www.eia.doe.gov/kids/energyfacts/science/formsofenergy.html