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

(Force and distance must be parallel to each other)

Joule (J) is the base unit of work

1 joule = 1 newton × 1 meter J = N × m

Work Example A student lifts a 50 pound (lb) ball 4 feet (ft) in 5 seconds (s). How many joules of work did the student complete?

Convert English units to SI units 1 1

lb ft

  4.45

N

0.305

m

50.0

lb

 4.45

1

lb N

4.00

ft

´  0.305

m

1

ft

Solve for Work 

W



222.5

N



1.22

m W

 271

J

222.5

N

= 1.22

m

 223

N

Energy Ability to do work Light, heat, mechanical, chemical, and electrical forms of energy can all be used to exert a force for a distance.

Roller coaster NASA solar sail Fuel cell

Forms of Energy Potential Energy (Stored energy, usually referring to gravitational energy) The capacity to do work by virtue of position or configuration

Forms of Energy Kinetic 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  Kinetic Radiant  Chemical Electrical  Thermal

Renewable Energy Sources Biomass Hydropower Geothermal Wind Solar

Nonrenewable Energy Sources Coal Natural Gas Petroleum Uranium

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

Energy Conversion Changing one form of energy to another Energy Efficiency: The ratio of the useful energy delivered by a dynamic system to the energy supplied to it Entropy: The increasing disorder when energy is transformed to heat during conversion Efficiency %  P out P in  100

Energy Conversion

Examples

Fossil fuels Solar cells Wind turbines Hydroelectric Nuclear Chemical → Heat → Mechanical → Electrical Sunlight → Electrical Kinetic → Mechanical → Electrical Gravitational potential → Mechanical → Electrical Nuclear → Heat → Mechanical → Electrical Vehicle System Conversion Chemical Mechanical Heat Which output is desired, mechanical or heat?

What Are Current Energy Concerns? Consumption Pollution Depletion Dependency Cost http://www.eia.doe.gov

What roles do engineers have in energy?

Power Rate at which work is performed or energy is expended P = W t Watt 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 A student lifts a 50.0 pound (lbf) ball 4.00 feet (ft) in 5.00 seconds (s). How many watts of power are used to lift the ball?

P = W t Work = 271.45 J P P   271.45J

5.00 s 54.3

J s 1 P J s   1Watt(W) 54.3 W

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