Glossary

5.1 Work

energy

the ability to do work

work

the transfer of energy by a force that causes an object to be displaced; the product of the component of the force in the direction of the displacement and the magnitude of the displacement

joule

SI unit of work and energy, equal to one newton-meter

5.2 Kinetic Energy and the Work-Energy Theorem

net work

work done by the net force, or vector sum of all the forces, acting on an object

work-energy theorem

the result, based on Newton’s laws, that the net work done on an object is equal to its change in kinetic energy

kinetic energy

the energy an object has by reason of its motion, equal to [latex]\frac{1}{2}{\text{mv}}^{2}[/latex] for the translational (i.e., non-rotational) motion of an object of mass [latex]m[/latex] moving at speed [latex]v[/latex]

5.3 Gravitational Potential Energy

gravitational potential energy
the energy an object has due to its position in a gravitational field

5.4 Conservative Forces and Potential Energy

conservative force

a force that does the same work for any given initial and final configuration, regardless of the path followed

potential energy

energy due to position, shape, or configuration

potential energy of a spring

the stored energy of a spring as a function of its displacement; when Hooke’s law applies, it is given by the expression [latex]\frac{1}{2}{\text{kx}}^{2}[/latex] where [latex]x[/latex] is the distance the spring is compressed or extended and [latex]k[/latex] is the spring constant

conservation of mechanical energy

the rule that the sum of the kinetic energies and potential energies remains constant if only conservative forces act on and within a system

mechanical energy

the sum of kinetic energy and potential energy

5.5 Nonconservative Forces

nonconservative force

a force whose work depends on the path followed between the given initial and final configurations

friction

the force between surfaces that opposes one sliding on the other; friction changes mechanical energy into thermal energy

thermal energy
the energy within an object due to the random motion of its atoms and molecules that accounts for the object’s temperature

5.6 Conservation of Energy

law of conservation of energy

the general law that total energy is constant in any process; energy may change in form or be transferred from one system to another, but the total remains the same

electrical energy

the energy carried by a flow of charge

chemical energy

the energy in a substance stored in the bonds between atoms and molecules that can be released in a chemical reaction

radiant energy

the energy carried by electromagnetic waves

nuclear energy

energy released by changes within atomic nuclei, such as the fusion of two light nuclei or the fission of a heavy nucleus

thermal energy

the energy within an object due to the random motion of its atoms and molecules that accounts for the object’s temperature

efficiency

a measure of the effectiveness of the input of energy to do work; useful energy or work divided by the total input of energy

5.7 Power

power

the rate at which work is done

watt

(W) SI unit of power, with [latex]\text{1 W}=\text{1 J/s}[/latex]

horsepower

an older non-SI unit of power, with [latex]\text{1 hp}=\text{746 W}[/latex]

kilowatt-hour

\(\left(\text{kW}\cdot h\right)[/latex] unit used primarily for electrical energy provided by electric utility companies

5.8 Work, Energy and Power in Humans

metabolic rate

the rate at which the body uses food energy to sustain life and to do different activities

basal metabolic rate

the total energy conversion rate of a person at rest

useful work

work done on an external system