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

The Joule (j) is the metric unit of work.

1 1 1joule newton meter

J N m

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 N

Convert 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

Definition: The ability to do work.

(light, heat, mechanical, chemical, electrical)

NASA solar sail Fuel cell Roller coaster

Forms of Energy - Potential Energy

Stored or gravitational energy. The capacity to do

work by virtue of position or configuration.

Forms of Energy - Kinetic Energy

The energy of motion. The energy a body

possesses because of its motion, which

occurs anywhere from an atomic level to

that of a whole organism.

Energy Transformation

The conversion of one form of energy into

another form.

Energy Transformation

Chemical

Radiant

Electrical

Renewable Energy Sources

Biomass Hydropower Geothermal

Wind Solar

Nonrenewable Energy Sources

Petroleum

Natural Gas Coal

Uranium

Conservation of Energy:

Energy 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 Conversion:

Changing one form of energy to another.

Energy Conversion

Examples

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 Heat

Which output is desired, mechanical or heat?

What Are Current Energy Concerns?

Consumption

What roles do engineers have in energy?

Pollution

Depletion

Dependency

Cost

http://www.eia.doe.gov

Power

Power is the rate at which work is

performed or energy is expended.

WP=

t

The watt is the base unit of power.

One watt is equal to 1 joule of work per

second.

Power is also measured in horsepower (HP).

Types of Power

Electrical Power:

Uses electrical energy to do work.

Mechanical Power:

Uses mechanical energy to do work (linear,

and rotary forms).

Fluid Power:

Uses energy transferred by liquids

(hydraulic) and gases (pneumatic).

Power Example

Power = Work / Time

Work = 271.45J

P

P

271.45 J

5.00 s

J54.3

s

P

J1 1Watt(W)s

54.3 W

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/formsof

energy.html