K- (a) The symbol for kelvin. (b) When in lower-case, the symbol for the prefix
kilo-.
kcal- The symbol for kilocalorie.
kelvin (KEL-vin)- The SI
unit of temperature. A temperature measured in kelvins (symbol K) indicates the number
of units above absolute zero. Since the divisions on the Kelvin scale and Celsius
scale are the same size, a change in temperature of one kelvin equals a change in
temperature of one Celsius degree.
Kelvin scale- A temperature scale whose
zero (called absolute zero) is the temperature at which it is impossible to extract
any more internal energy from a material. 0 K -2730C. There are no negative temperatures
on the Kelvin scale.
kg- The symbol for kilogram.
kilocalorie- (KIL-o-kal-er-ee)
A unit of heat. One kilocalorie equals 1000 calories, or the amount of heat required
to raise the temperature of one kilogram of water by 1'C
kilogram- (KIL-o-gram)
The fundamental SI unit of mass. One kilogram (symbol kg) is the amount of mass in
one liter of water at 40C. See Appendix A.
kinetic energy- (kih-NET-ik) Energy
of motion, equal (nonrelativistically) to half the mass multiplied by the speed squared.
km- The symbol for kilometer:
L- The symbol for liter:
laser-
(LAY-zer) An optical instrument that produces a beam of coherent light-that is, having
the waves all the same frequency, phase, and direction.
law- A general hypothesis
or statement about the relationship of natural quantities that has been tested over
and over again and has not been contradicted. Also known as a principle.
law
of conservation of angular momentum- An object or system of objects will maintain
a constant angular momentum unless acted upon by an unbalanced external torque.
law
of conservation of energy- Energy cannot be cre-ated or destroyed. It may be transformed
from one form into another, but the total amount of energy never changes.
law
of conservation of momentum- In the absence of a net external force, the momentum
of an object or system of objects is unchanged.
law of inertia- Every body
continues in its state of rest, or of motion in a straight line at constant speed,
unless it is compelled to change that state by a net force exerted upon it. Also
known as Newton's first law.
law of reflection- The angle of incidence for
a wave that strikes a surface is equal to the angle of reflection. This is true for
both partially and totally reflected waves.
law of universal gravitation-
For any pair of objects, each object attracts the other object with a force that
is directly proportional to the product of the masses of the objects, and inversely
proportional to the square of the distance between their centers of mass.
lens-
(LENZ) A piece of glass (or other transparent material) that can bend parallel rays
of light so that they cross, or appear to cross, at a single point.
lever-
(LEH-ver, LEE-ver) A simple machine, made of a bar that turns about a fixed point.
lever arm- The perpendicular distance between an axis and the line of action
of a force that tends to produce rotation about that axis.
lift- In application
of Bernoulli's principle, the net upward force produced by the difference between
upward and downward pressures. When lift equals weight, horizontal flight is possible.
light-year- The distance light travels through a vac-uum during one year.
line spectrum- Pattern of distinct lines of color, cor-responding to particular
wavelengths, that are seen in a spectroscope when a hot gas is viewed.
linear
momentum- Product of the mass and the velocity of an object. Also called momentum.
(This definition applies at speeds much less than the speed of light.)
linear
speed- The path distance moved per unit of time. Also called simply speed.
longitudinal
wave- (lon-jih-TEWD-ih-nul) A wave in which the vibration is in the same direction
as that in which the wave is traveling, rather than at right angles to it.
lunar
eclipse- The cutoff of light from the full moon when the earth is directly between
the sun and the moon, so that the earth's shadow is cast on the moon.
m- (a) The symbol for meter: (b) When in italic, the symbol for mass.
machine-
A device for increasing (or decreasing) a force or simply changing the direction
of a force.
magnetic domain- A microscopic cluster of atoms with their magnetic
fields aligned.
magnetic field- A force field that fills the space around
every magnet or current-carrying wire. Another magnet or current-carrying wire intro-duced
into this region will experience a magnetic force.
magnetic pole- One of
the regions on a magnet that produces magnetic forces.
mass- A measure of
an object's inertia; also a measure of the amount of matter in an object. Depends
only on the amount of and kind of particles that com-pose an object-not on its location
(as weight does).
mechanical advantage- The ratio of output force to input
force for a machine.
mechanical energy- The energy due to the position or
the movement of something; potential or kinetic energy (or a combination of both).
mirage- (mih-RAHZH) A floating image that appears in the distance and is
due to the refraction of light in the earth's atmosphere.
molecule- (MOL-uh-kyool)
Two or more atoms of the same or different elements bonded to form a larger particle.
momentum- The product of the mass and the velocity of an object (provided
the speed is much less than the speed of light). Has magnitude and direction (a vector
quantity). Also called linear momentum.
monochromatic- (mon'-o-kro-MAT'-ik)
Having a single color or frequency.
muon- (MEW-on) A short-lived subatomic
particle with a mass that is 207 times that of an electron; may be positively or
negatively charged.
N- The symbol for newton.
natural frequency-
A frequency at which an elastic object, once energized, will vibrate. Minimum energy
is required to continue vibration at that frequency. Also called resonant frequency
neap tide- A tide that occurs when the moon is hallway between a new moon
and a full moon, in either direction. The tides due to the sun and the moon partly
cancel, so that the high tides are lower than average and the low tides are not as
low as average.
nearsighted- Term applied to a person who can clearly see
nearby objects but not clearly see distant objects. Eyeball is elongated so that
images focus in front rather than on the retina.
net force- The combination
of all the forces that act on an object.
neutral equilibrium- The state of
an object balanced so that any small movement neither raises nor lowers its center
of gravity
neutron- An electrically neutral particle that is one of the two
kinds of particles that compose an atomic nucleus.
newton- SI unit of force.
One newton (N) is the force applied to a one-kilogram mass that will produce an acceleration
of one meter per second per second.
Newton's first law- See law of inertia.
Newton's law of cooling- The rate of cooling of an object-whether by conduction,
convection, or radiation is approximately proportional to the temperature difference
between the object and its surroundings.
Newton's second law- The acceleration
produced by a net force on a body is directly proportional to the magnitude of the
net force, is in the same direction as the net force, and is inversely proportional
to the mass of the body.
Newton's third law- whenever one body exerts a force
on a second body the second body exerts an equal and opposite force on the first.
node- Any part of a standing wave that remains stationary
normal-
A line perpendicular to a surface.
normal force- For an object resting on
a horizontal surface, the upward force that balances the weight of the object; also
called the support force
nuclear fission- (FIH-shun) The splitting of an
atomic nucleus, particularly that of a heavy element such as uranium-235, into two
main parts accompanied by the release of much energy
nuclear fusion- (Few-zhun)
The combining of nuclei of light atoms, such as hydrogen, into heavier nuclei accompanied
by the release of much energy
nucleon- (NEW-Mee-on) The principal building
block of the nucleus; a neutron or a proton.
nucleus- The positively charged
center of an atom, which contains protons and neutrons and has almost all the mass
of the entire atom but only a tiny fraction of the volume.
objective lens- In an optical device using compound lenses, the lens closest to
the objectobserved.
ohm- (OM) The SI unit of electrical resistance. One ohm
(symbol Q) is the resistance of a device that draws a current of one ampere when
a voltage of one volt is impressed across it.
Ohm's law- The statement that
the current in a circuit is directly proportional to the voltage impressed across
the circuit, and is inversely proportional to the resistance of the circuit.
opaque-
Term applied to materials that absorb light without reemission, and consequently
do not allow light through them.
optical fiber- A transparent fiber, usually
of glass or plastic, that can transmit light down its length by means of total internal
reflection.
out- of phase Term applied to two waves for which the crest of
one wave arrives at a point at the same time that a trough of the second wave arrives.
Their effects cancel each other.
parallel circuit- An electric circuit in
which devices are connected to the same two points of the circuit, so that any single
device completes the circuit inde-pendently of the others.
pascal- (pas-KAL)
The SI unit of pressure. One pascal (symbol Pa) of pressure exerts a normal force
of one newton per square meter.
Pascal's principle- Changes in pressure at
any point in an enclosed fluid at rest are transmitted undiminished to all points
in the fluid and act in all directions.
penumbra- A partial shadow that appears
where light from part of the source is blocked and light from another part of the
source is not blocked.
perigee- (PEH-rih-jee) The point in a satellite's
elliptical orbit where it is nearest the center of the earth.
period- (a)
The time required for a complete orbit. (b) The time required for a pendulum to make
one to-and-fro swing. In general, the time required to complete a single cycle.
periodic
table- A chart that lists elements by atomic number and by electron arrangements,
so that elements with similar chemical properties are in the same column.
perturbation-
The deviation of an orbiting object from its path around a center of force caused
by the action of an additional center of force.
phase- One of the four possible
forms of matter: solid, liquid, gas, and plasma. Often called state
photoelectric
effect- The ejection of electrons from certain metals when exposed to certain frequencies
of light.
photon- (FO-ton) In the particle model of electromagnetic radiation,
a particle that travels only at the speed of light and whose energy is related to
the frequency of the radiation in the wave model.
pigment- A material that
selectively absorbs colored light.
pitch- Term that refers to how high or
low sound frequencies appear to be.
Planck's constant- A fundamental constant
of quantum theory that determines the scale of the small-scale world. Planck's constant
(symbol h) multiplied by the frequency of radiation gives the energy of a photon
of that radiation.
plasma- (PLAZ-muh) A fourth phase of matter, in addition
to solid, liquid, and gas. In the plasma phase, which exists mainly at high temperature,
matter consists of positively charged ions and free electrons.
polarization-
(po-ler-ih-ZAY'-shun) The aligning of vibrations in a transverse wave, Usually by
filtering out waves of other directions.
postulate- (POS-tyoo-lit) A fundamental
assumption.
potential- See electric potential.
potential difference-
The difference in electric potential (voltage) between two points. Free charge flows
when there is a difference, and will continue until both points reach a common potential.
potential energy- Energy of position, usually related to the relative position
of two things, such as a stone and the earth, or an electron and a nucleus.
power-
Rate at which work is done or energy is transformed, equal to the work done or energy
transformed divided by time; measured in watts.
pressure- Force per surface
area where the force is normal to the surface; measured in pascals.
principal
axis- The line joining the centers of curva-ture of the surfaces of a lens.
principle-
A general hypothesis or statement about the relationship of natural quantities that
has been tested over and over again and has not been contradicted; also known as
a law.
principle of floatation- A floating object displaces a quantity of
fluid of a weight equal to its own weight.
projectile- Any object that moves
through the air or through space, acted on only by gravity (and air resistance, if
any).
proton- A positively charged particle that is one of the two kinds
of particles found in the nucleus of an atom.
pulley- A type of lever that
is a wheel with a groove in its rim, and one that is used to change the direction
of a force. A pulley or system of pulleys can also multiply forces.
pupil-
The opening in the eyeball through which light passes.
quantum- (p1. quanta) (KWONT-um) The fundamental"size" unit; the smallest
amount of anything. One quantum of light energy is called a photon.
quantum
mechanics- The branch of physics that is the study of the motion of particles in
the microworld of atoms and nuclei.
quantum physics- The branch of physics
that is the general study of the microworld of photons, atoms, and nuclei.
quark-
(KWORK, KWARK) One of the elementary par-ticles of which nucleons (protons and neutrons)
are made.
radiant energy- Any energy including heat, light, and X rays,
that is transmitted by radiation. It occurs in the form of electromagnetic waves.
radiation- (a) Energy transmitted by electromagnetic waves. (b) The particles
given off by radioactive atoms such as uranium.
radioactive- Term applied
to an atom with a nucleus that is unstable and that can spontaneously emit a particle
and become the nucleus of another element.
rarefaction- (rayr-uh-FAK- shun)
A disturbance in air (or matter) in which the pressure is lowered. Opposite of compression.
rate- In physics, how fast something happens, or how much something changes
per unit of time; a change in a quantity divided by the time it takes for the change
to occur.
ray- A thin beam of light.
ray diagram- A diagram showing
rays that can be drawn to determine the size and location of an image formed by a
mirror or lens.
reaction force- The force that is equal in strength and opposite
in direction to the action force, and one that acts simultaneously on whatever is
exerting the action force.
real image- An image that is formed by converging
light rays and that can be displayed on a screen.
red shift- A decrease in
the measured frequency of light (or other radiation) from a receding source; called
the red shift because the decrease is toward the low-frequency, or red, end of the
color spectrum.
reflection- The bouncing back of a particle or wave that
strikes the boundary between two media.
refraction- The change in direction
of a wave as it crosses the boundary between two media in which the wave travels
at different speeds.
regelation- The phenomenon of ice melting under pressure
and freezing again when the pressure is reduced.
relative- Regarded in relation
to something else. Depends on point of view, or frame of reference. Sometimes referred
to as "with respect to."
relative humidity- A ratio between how
much water vapor is in the air and the maximum amount of water vapor that could be
in the air at the same temperature.
relativistic kinetic energy- Kinetic
energy at very high speeds approaching the speed of light.
relativistic momentum-
Momentum at very high speeds approaching the speed of light.
resolution-
(rez-uh-LOO-shun) (a) The process of resolving a vector into components. (b) In optics,
a measure of how well closely adjacent optical images are distinguished.
resonance-
(REZ-uh-nuns) A phenomenon that occurs when the frequency of forced vibrations on
an object matches the object's natural frequency, and a dramatic increase in amplitude
results.
rest energy- The "energy of being" given the equa-tion,
E = mc^2
rest mass- The intrinsic mass of an object, a fixed property independent
of speed or energy.
resultant- (rih-ZUL-tunt) The vector sum of two or more
component vectors.
retina- (RET-ih-nuh) The layer of light-sensitive tissue
at the back of the eye.
reverberation- (nh-verb -er-AY- shun) Persistence
of a sound, as in an echo, due to multiple reflections.
revolution- Motion
of an object turning around an axis outside the object.
rotation- The spinning
motion that takes place when an object rotates about an axis located within the object
(usually an axis through its center of mass).
rotational inertia- The reluctance
of an object to change its state of rotation, determined by the distribution of the
mass of the object and the location of the axis of rotation or revolution.
rotational
speed- The number of rotations or revolu-tions per unit of time; often measured in
rotations or revolutions per second or per minute (RPM).
rotational velocity-
Rotational speed together with a direction for the axis of rotation or revquantum-
(p1. quanta)
S- The symbol for second.
satellite- An object that falls around the earth
or some other body rather than falling into it.
saturated- Term applied to
a substance, such as air, that contains the maximum amount of another substance,
such as water vapor, at a given temperature and pressure.
scalar quantity-
A quantity in physics, such as mass, volume, and time, that can be completely specified
by its magnitude, and has no direction.
scaling- The study of how size affects
the relationship between weight, strength, and surface area.
scatter- To
absorb sound or light and reemit it in all directions.
schematic diagram-
Diagram that describes an elec-tric circuit, using special symbols to represent different
devices in the circuit.
scientific method- An orderly method for gaining,
organizing, and applying new knowledge.
second law of thermodynamics- Heat
will never of itself flow from one object to another of higher temperature.
second
postulate of special relativity- The speed of light in empty space always has the
same value regardless of the motion of the source or the motion of the observer.
semiconductor- Material that can be made to behave as either a conductor
or an insulator of electricity.
series circuit- An electric circuit in which
devices are arranged so that charge flows through each in turn. If one part of the
circuit should stop the current, it will stop throughout the circuit.
shadow-
A shaded region that results when light falls on an object and thus cannot reach
into the region on the far side of the object.
shell model of the atom- A
model in which the elec-trons of an atom are pictured as grouped in concentric shells
around the nucleus.
shock wave- A cone-shaped wave produced by an object
moving at supersonic speed through a fluid.
simple harmonic motion- Periodic
motion in which acceleration is proportional to the distance from an equilibrium
position and is directed toward that equilibrium position.
sine curve- A
curve whose shape represents the crests and troughs of a wave, as traced out by a
swinging pendulum that drops a trail of sand over a moving conveyor belt.
solar
eclipse- The cutoff of light from the sun to an observer on the earth when the moon
is directly between the sun and the earth.
sonic boom- The sharp crack heard
when the shock wave that sweeps behind a supersonic aircraft reaches the listener.
space-time- A combination of space and time, which are viewed in special
relativity as two parts of one whole.
special theory of relativity- The theory
introduced in 1905 by Albert Einstein, that describes how time is affected by motion
in space at a constant velocity and how mass and energy are related.
specific
gravity- The ratio of the mass (or weight) of a substance to the mass (or weight)
of an equal volume of water.
specific heat capacity- The quantity of heat
required to raise the temperature of a unit mass of a substance by one degree Celsius.
Often simply called "specific heat," or "heat capacity."
spectroscope-
An instrument used to separate the light from a hot gas or other light source into
its constituent frequencies.
spectrum- For sunlight and other white light,
the spread of colors seen when the light is passed through a prism or diffraction
grating. In general, the spread of radiation by frequency, so that each frequency
appears at a different position.
.
speed- How fast something is moving; the
path distance moved per time. The magnitude of the velocity vector.
spring
tide- A high or low tide that occurs when the sun, earth, and moon are all lined
up so that the tides due to the sun and moon coincide, making the high tides higher
than average and the low tides lower than average.
stable equilibrium- The
state of an object balanced so that any small displacement or rotation raises its
center of gravity
standing wave- Wave in which parts of the wave remain stationary
and the wave appears not to be traveling. The result of interference between an incident
(original) wave and a reflected wave.
streamline- The smooth path of a small
region of fluid in steady flow.
strong force- The force that attracts nucleons
to each other within the nucleus; a force that is very strong at close distances
but decreases rapidly as the distance increases.
subtractive primary colors-
The colors of magenta, yellow and cyan. These are the three colors most useful in
color mixing by subtraction.
superconductor- Material that has infinite conductivity
at very low temperatures, so that charge flows through it without resistance.
support
force- Force that completely balances the weight of an object at rest.
tangential speed- The speed of an object moving along a circular path.
tangential
velocity- Component of velocity tangent to the trajectory of a projectile.
telescope-
Optical instrument that forms images of very distant objects.
temperature-
The property of a material that tells how warm or cold it is relative to some standard.
In an ideal gas, the molecular kinetic energy per molecule.
terminal speed-
The speed at which the acceleration of a falling object is zero because friction
balances the weight.
terminal velocity- Terminal speed together with the
direction of motion (down for falling objects).
terrestrial radiation- Radiant
energy emitted from the earth.
theory- A synthesis of a large body of information
that encompasses well-tested and verified hypotheses about aspects of the natural
world.
thermal contact- The state of two or more objects or substances in
contact such that it is possible for heat to flow from one object or substance to
another.
thermal equilibrium- The state of two or more objects or substances
in thermal contact when they have reached a common temperature.
thermodynamics-
The study of heat and its transfor-mation to mechanical energy.
thermonuclear
fusion- Nuclear fusion brought about by extremely high temperatures.
thermostat-
A type of valve or switch that responds to changes in temperature and that is used
to control the temperature of something.
time dilation- An observable stretching,
or slowing, of time in a frame of reference moving past the
observer at a speed
approaching the speed of light.
torque- (TORK) The rotational analog of force;
the product of force and the lever arm (measured in newton-meters). Torque tends
to produce rota-tional acceleration.
total internal reflection- The 100%
reflection (with no transmission) of light that strikes the boundary between two
media at an angle greater than the critical angle.
transformer- A device
for increasing or decreasing voltage through electromagnetic induction.
transmutation-
The conversion of an atomic nucleus of one element into an atomic nucleus of another
element through a loss or gain in the number of protons.
transparent- Term
applied to materials that allow light to pass through them in straight lines.
transverse
wave- A wave with vibration at right angles to the direction the wave is traveling.
trough- (TRAWF) One of the places in a wave where the wave is lowest or the
disturbance is greatest in the opposite direction from a crest.