absolute zero
the lowest possible temperature, at which all molecular motion would cease and a gas would have no volume
acceleration
the rate of change in velocity
action-reaction forces
the pair of forces that are equal in magnitude and opposite in direction; these forces are involved in the same interaction, but act on different objects
adiabatic
the expansion or compression of a gas without a gain or loss of heat
air resistance
the opposing force the air exerts on an object moving through it
alpha decay
the process by which a radioactive element emits an alpha particle
alpha particle
positively charged particle consisting of two protons and two neutrons
alternating current
electric current that rapidly reverses its direction
ammeter
device used to measure electrical current
ampere
unit of electrical current equal to one coulomb per second
amplitude
maximum displacement from equilibrium position; the distance from the midpoint of a wave to its crest or trough
angle of incidence
the angle between the normal line to a surface and the incident ray or wave
angle of reflection
the angle between the normal line to a surface and the reflected ray or wave
angle of refraction
the angle between the normal line to a surface and the refracted ray or wave at the boundary between two media
angular momentum
the conserved rotational quantity that is equal to the product of the mass, velocity, and radius of motion
antinode
point of maximum displacement of two or more waves constructively interfering
atom
the smallest particle of an element that can be identified with that element; consists of protons and neutrons in the nucleus, and electrons in motion around the nucleus
atomic mass unit
the unit of mass equal to 1/12 the mass of a carbon-12 nucleus
atomic number
the number of protons in the nucleus of an atom
average acceleration
the acceleration of an object measured over a time interval; the total change in velocity divided by the total time taken to achieve that velocity
average velocity
the velocity of an object measured over a time interval; the total change in displacement divided by the total time taken to achieve that displacement
battery
device that converts chemical energy into electrical energy, creating a potential difference (voltage)
beta decay
the emission of an electron from the nucleus of a radioactive element as a result of a neutron decaying into a proton
beta particle
high speed electron emitted from a radioactive element when a neutron decays into a proton
binding energy
the nuclear energy that binds protons and neutrons in the nucleus of the atom
boiling point
temperature at which a substance boils at normal atmospheric pressure, changing from a liquid to a vapor state
calorie
the amount of heat required to raise the temperature of one gram of water by one degree Celsius
calorimeter
device that isolates objects to measure temperature changes due to heat flow
capacitance
ratio of the charge stored on a conductor per unit voltage
capacitor
electrical device used to store charge and energy in an electric field
Carnot efficiency
the ideal efficiency of a heat engine or refrigerator working between two constant temperatures
center of mass
the point that represents the average location of all the mass in a system; for a rigid object, it is the point at which all of the mass of an object can be considered concentrated
centripetal acceleration
for an object moving in circular motion, the acceleration that is directed toward the center of the circular path
centripetal force
the central force causing an object to move in a circular path
chain reaction
nuclear process producing more neutrons, which in turn can create more nuclear processes, usually applied to fission
charge
the fundamental quantity that underlies all electrical phenomena
charging by conduction
transfer of charge by actual contact between two objects
charging by induction
transfer of charge by bringing a charged object near a conductor, then grounding the conductor
circular motion
motion of an object moving at a constant radius in a circular path
closed system
a system that can exchange energy but cannot exchange matter with the surroundings
coefficient of friction
ratio of the frictional force between two surfaces and the normal force between the surfaces
component
the shadow or projection of a vector on a particular coordinate axis
compound
chemical substance consisting of two or more different elements combined in a fixed proportion
concave lens
a lens that is thinner in the center than at the edges; also known as a diverging lens
concave mirror
a mirror that converges light rays to a focal point; also known as a converging mirror
conductor
a material through which heat or electric current can easily flow
conservation of charge
law stating that the total charge in a system must remain constant during any process
conserved properties
any properties that remain constant during a process
constant acceleration
acceleration that does not change during a time interval
constant velocity
velocity that does not change during a time interval
constructive interference
addition of two or more waves that are in phase, resulting in a wave of increased amplitude
convection
heat transfer by the movement of a heated substance, such as currents in a fluid
conventional current
the movement of positive charges through a conductor
converging lens
a lens that converges light rays to a focal point; also known as a convex lens
convex lens
a lens that is thicker in the center than at the edges; also known as a converging lens
convex mirror
a mirror that diverges light rays; also known as a diverging mirror
cosine
the ratio of the adjacent side of an angle in a right triangle to the hypotenuse
coulomb
the unit for electric charge
Coulomb’s law
the electric force between two charges is proportional to the product of the charges and inversely proportional to the square of the distance between them
crest of a wave
the highest point on a wave
critical angle
the minimum angle for light entering a different medium at which total internal reflection will occur
critical mass
the minimum amount of mass of fissionable material necessary to sustain a nuclear chain reaction
de Broglie wavelength
the wavelength associated with a moving particle with a momentum mv
density
the ratio of the mass to the volume of a substance
destructive interference
addition of two or more waves that are out of phase, resulting in a wave of decreased amplitude
diffraction
the spreading of a wave beyond the edge of a barrier or through an opening
diffraction grating
material containing many parallel lines that are very closely spaced so that when light is passed through the lines, an interference pattern is produced
diffuse reflection
reflection of light in many directions by a rough surface
direct current
electric current whose flow of charges is in one direction only
dispersion of light
the separation of light into its component colors using a prism or diffraction grating
displacement
change in position in a particular direction (vector)
distance
the length moved between two points (scalar)
diverging lens
a lens that is thinner in the middle than at the edges that diverges light rays passing through it; also known as a concave lens
Doppler effect
the apparent change in frequency of a sound or light source due to relative motion between the source and the observer
dynamics
the study of the causes of motion (forces)
elastic collision
a collision in which both momentum and kinetic energy are conserved
electric circuit
a continuous closed path in which electric charges can flow
electric current
flow of charged particles; conventionally, the flow of positive charges
electric field
the space around a charge in which another charge will experience a force; electric field lines always point from positive charge to negative charge
electric generator
a device that uses electromagnetic induction to convert mechanical energy into electrical energy
electric potential
the amount of work per unit charge to move a charge from a very distant point to another point in an electric field
electric potential difference
the difference in potential between two points in an electric field; also known as voltage
electromagnet
a magnet with a magnetic field produced by an electric current
electromagnetic induction
inducing a voltage in a conductor by changing the magnetic field around the conductor
electromagnetic wave
a wave produced by the vibration of an electric field and a magnetic field, which propagates itself through space at a very high speed
electron
the smallest negatively charged particle
electrostatics
the study of electric charge, field, and potential at rest
element
a substance made of only one kind of atom
elementary charge
the smallest existing charge; the charge on one electron or one proton (1.6 × 10–19 C)
ellipse
an oval-shaped curve that is the path taken by a point that moves such that the sum of its distances from two fixed points (foci) is constant; the planets move in elliptical orbits around the Sun
emf
electromotive force; another name for voltage, particularly voltage induced in a conductor by electromagnetic induction
energy
the nonmaterial quantity that is the ability to do work on a system
energy level
amount of energy an electron has while in a particular orbit around the nucleus of an atom
entropy
the measure of the amount of disorder in a system
equilibrant
the vector that can balance a resultant vector; the force that can put a system in equilibrium
equilibrium
condition of a system in which the vector sum of the forces and torques is equal to zero
equivalent resistance
the single resistance that could replace the individual resistances in a circuit and produce the same result
evaporation
the process by which a liquid changes into a gas
excited state
the energy level of an electron in an atom after the electron has absorbed energy
external force
force exerted from outside the defined system
farad
the unit for capacitance equal to one coulomb per volt
Faraday’s law of induction
law stating that a voltage can be induced in a conductor by changing the magnetic field around the conductor
first law of thermodynamics
the heat lost by a system is equal to the heat gained by the system minus any work done by the system; conservation of energy
fission
the splitting of a large nucleus into two smaller ones
fluid
any substance that flows, typically a liquid or a gas
focal length
the distance between the center of a lens or mirror to the point at which the incoming parallel rays converge at the focal point
focal point
the point at which incoming parallel light rays converge or appear to originate
force
any influence that tends to accelerate an object; a push or a pull
frame of reference
point of view or coordinate system used to study motion
free fall
motion under the influence of gravity
frequency
the number of vibrations or revolutions per unit of time
friction
the force that acts to resist the relative motion between two rough surfaces that are in contact with each other
fundamental overtone
lowest frequency sound produced by a musical instrument
fundamental particles
the particles (quarks and leptons) of which all matter is composed
fusion
the combining of two light nuclei into a heavier one with a release of energy
galvanometer
device used to measure small electrical currents
gamma decay
process by which a radioactive element emits a gamma ray
gamma ray
high energy electromagnetic wave emitted by a radioactive nucleus
gas
a state of matter that expands to fill a container
gravitational field
space around a mass in which another mass will experience a force
gravitational force
the force of attraction between two objects due to their masses
gravitational potential energy
the energy a mass has because of its position in a gravitational field
grounding
the process of connecting a charged object to the earth or a large conductor to remove its excess charge
ground state
the lowest energy state of an electron in an atom
half-life
the time it takes for half the atoms in a radioactive sample to decay
heat
the energy that is transferred from one body to another because of a temperature difference
heat engine
device that changes internal energy into mechanical work
heat of fusion
energy needed to change a unit mass of a substance from a solid to a liquid state at the melting point
heat of vaporization
energy needed to change a unit mass of a substance from a liquid to a gaseous state at the boiling point
Heisenberg uncertainty principle
the more accurately one determines the position of a subatomic particle, the less accurately its momentum is known, and vice versa
hertz
the unit for frequency equal to one cycle or vibration per second
Hooke’s law
the displacement (stretch) of a spring is proportional to the force applied to it
hypotenuse
the side opposite to the right angle in a right triangle
image
reproduction of an object using lenses or mirrors
impulse
the product of the force acting on an object and the time over which it acts
impulse-momentum theorem
the impulse imparted to an object is equal to the change in momentum it produces
incandescent body
an object that emits light because of its high temperature
index of refraction
the ratio of the speed of light in a vacuum to the speed of light in another medium
inelastic collision
a collision in which only momentum is conserved, and not kinetic energy
inertia
the tendency of an object to not change its state of rest or motion at a constant velocity; mass is a measure of inertia
inertial reference frame
a reference frame that is at rest or moving with a constant velocity; Newton’s laws are valid within any inertial reference frame
infrared
electromagnetic waves of frequencies just below those of red visible light
initial velocity
the velocity at which an object starts at the beginning of a time interval
in phase
term applied to two or more waves whose crests and troughs arrive at a place at the same time in such a way as to produce constructive interference
instantaneous acceleration
the acceleration of an object at a particular instant of time
instantaneous position
the position of an object at a particular instant of time
instantaneous velocity
the velocity of an object at a particular instant of time
insulator
a material that is a poor conductor of heat or electric current due to a poor supply of free electrons
interference of waves
displacements of two or more waves in the same medium at the same time, producing either larger or smaller waves
internal forces
forces between objects in the same system
inverse relationship
relationship between two variables that change in opposite directions, so that if one is doubled the other is reduced to one-half
inverse square law
situation where one physical quantity varies as the inverse square of the distance from its source
isolated system
a collection of objects not acted upon by any external forces and which energy neither enters or exits
isotope
a form of an element that has a particular number of neutrons; has the same atomic number but a different mass number than the other isotopes that occupy the same place on the periodic table
joule
the unit for energy equal to one Newton-meter
joule heating
the increase in temperature in an electrical conductor due to the conversion of electrical energy into heat energy
Joule’s law of heating
the heating power of an electric current through a resistance is equal to the product of the current and the voltage across the resistor
Kelvin (absolute) temperature scale
scale in which zero Kelvins is defined as absolute zero, the temperature at which all molecular motion ceases
Kepler’s laws
the three laws of motion for objects, such as the planets and the Sun, attracted to each other by the gravitational force
kilogram
the fundamental unit of mass
kilowatt-hour
amount of energy equal to 3.6 × 106 joules, usually used in electrical measurement
kinematics
the study of how motion occurs, including distance, displacement, speed, velocity, acceleration, and time
kinetic energy
the energy a mass has by virtue of its motion
kinetic molecular theory
the description of matter as being made up of extremely small particles that are in constant motion
laser
light amplification by stimulated emission of radiation; laser light is coherent and monochromatic (i.e., all the waves are of the same wavelength and are in phase with each other)
law of conservation of energy
the total energy of a system remains constant during a process
law of conservation of momentum
the total momentum of a system remains constant during a process
law of inertia
see Newton’s first law
law of reflection
the angle of incidence of an incoming wave is equal to the angle of reflection measured from a line normal (perpendicular) to the surface
law of universal gravitation
the gravitational force between two masses is proportional to the product of the masses and inversely proportional to the square of the distance between them
lens
a piece of transparent material that can bend light rays to converge or diverge
lever arm
perpendicular distance from the axis of rotation to a line of force producing or potentially producing the rotation
light
the range of electromagnetic waves that is visible to the human eye; alternately used by physicists to refer to the entire range of electromagnetic radiation
linear accelerator
device used to accelerate subatomic particles to high energies so that they may be more easily studied
linear relationship
relationship between two variables that are proportional to each other
linear restoring force
a force such as a spring force in which the force is proportional to the displacement (stretch) and opposite to the direction of the displacement
line spectrum
discrete lines emitted by a cool excited gas
liquid
substance that has a fixed volume, but assumes the shape of its container
lodestone
a naturally occurring magnetic rock made principally of iron
longitudinal wave
wave in which the vibration of the medium is parallel to the direction of motion of the wave
loudness
the quality of a sound wave that is measured by its amplitude
magnetic domain
cluster of magnetically aligned atoms
magnetic field
the space around a magnet in which another magnet or moving charge will experience a force
magnification
ratio of the size of an optical image to the size of the object
mass defect
the mass equivalent of the binding energy in the nucleus of an atom by E = mc2
mass number
the total number of protons and neutrons in the nucleus of a particular atom
matter wave
the wave associated with a mass having a momentum according to the de Broglie hypothesis
mechanical energy
the sum of the potential and kinetic energies in a system
mechanical resonance
condition in which natural oscillation frequency equals frequency of driving force
mechanical wave
a wave that needs a medium through which to travel
melting point
the temperature at which a substance changes from a solid to a liquid state
meter
the SI unit of length
molecule
two or more atoms joined to form a larger particle
momentum
the product of the mass of an object and its velocity
monochromatic light
light having a single color or frequency
net force
the vector sum of the forces acting on an object
neutral
having no net charge
neutron
an electrically neutral subatomic particle found in the nucleus of an atom
newton
the SI unit for force equal to the force needed to accelerate one kilogram of mass by one meter per second squared
Newton’s first law of motion
every body continues in its state of rest or at a constant velocity unless acted on by an unbalanced force; also known as the law of inertia
Newton’s second law of motion
a net force acting on a mass causes an acceleration that is proportional to and in the direction of the force and inversely proportional to the mass of the object
Newton’s third law of motion
for every action force there is an equal and opposite reaction force
node
the point of minimum displacement in a standing wave
noninertial reference frame
a reference frame that is accelerating; Newton’s laws are not valid within a noninertial reference frame
normal
a line that is perpendicular to a surface
normal force
the reaction force of a surface on an object when an object is in contact with the surface; always acts perpendicularly to the surface
nuclear fission
the splitting of a heavy nucleus into smaller fragments with the release of energy
nuclear fusion
the combining of two light nuclei into one larger one with the release of energy
nuclear reaction
any process in the nucleus of an atom that causes the number of protons and/or neutrons to change
nuclear reactor
device in which nuclear fission or fusion is used to generate electricity
nucleon
either a proton or a neutron in the nucleus of an atom
object (optics)
the source of diverging light rays
ohm
the SI unit for resistance equal to one volt per ampere
Ohm’s law
the ratio of voltage to current in a circuit is a constant called resistance
opaque
material that will not transmit light
open system
a system that can exchange both matter and energy with the surroundings
out of phase
term applied to two or more waves when the crest of one wave arrives at a point at the same time as the trough of a second wave arrives, producing destructive interference
parallel circuit
an electric circuit that has two or more paths for the current to follow, allowing each branch to function independently of the others
Pascal
the SI unit for pressure equal to one newton of force per square meter of area
period
the time for one complete cycle or revolution
periodic motion
motion that repeats itself at regular intervals of time
photoelectric effect
the ejection of electrons from certain metals when exposed to light of a minimum frequency
photon
the smallest particle (quantum) of light
physics
the study of matter and energy and all their relationships
pitch
the perceived characteristic of a sound that is equivalent to its frequency
Planck’s constant
the quantity that results when the energy of a photon is divided by its frequency
plane mirror
smooth, flat surface that reflects light regularly
polarized light
light in which the electric fields are all in the same plane
position
the distance between an object and a reference point
position-time graph
the graph of the motion of an object that shows how its position varies with time
power
the rate at which work is done or energy is dissipated
pressure
force per unit area
primary light colors
red, green, or blue light
principal axis
the line connecting the center of curvature of a curved mirror with its geometrical vertex; the line perpendicular to the plane of a lens passing through its center
principle of superposition
the displacement due to two or more interfering waves is equal to the sum of the displacement of the individual waves
projectile
any object that is projected by a force and continues to move by its own inertia in a gravitational field
proton
subatomic particle with positive charge that is the nucleus of a hydrogen atom
quantized
occuring in multiples of some smallest possible increment (quantum); refers to quantities
quantum mechanics
the study of the properties of matter using its wave properties
quantum model of the atom
atomic model in which only the probability of locating an electron is known
quark
one of the elementary particles of which all protons and neutrons are made
radiation
the transmission of energy by electromagnetic waves, or the particles given off by radioactive atoms
radioactive decay
the spontaneous change of unstable nuclei into other nuclei
range of a projectile
the horizontal distance between the launch point of a projectile and where it returns to its launch height
ray model of light
light may be represented by a straight line along the direction of motion
ray optics
study of light using the ray model
real image
an image that can be projected onto a screen
reference point
zero location in a coordinate system
refraction
the bending of a wave due to a change in medium
resistance
the ratio of the voltage across a device to the current running through it
resistor
device designed to have a specific resistance to electric current
resultant
the vector sum of two or more vectors
right-hand rules
used to find the magnetic field around a current-carrying wire or the force acting on a wire or charge in a magnetic field
Rutherford’s model of the atom
the first nuclear model of the atom (1911)
scalar
a quantity in physics, such as mass, that can be completely described by its magnitude or size, without regard to direction
schematic diagram
a diagram using special symbols to represent a circuit
scientific notation
numbers represented as a mantissa times a power of ten, such as 3 × 108
second
the SI unit of time
second law of thermodynamics
heat flows naturally from a region of higher temperature to a lower temperature; all natural systems tend toward a state of higher disorder
series circuit
an electric circuit in which devices are arranged so that charge flows through each equally
SI
Systeme Internationale; agreed-upon method of using the metric system of measurement
simple harmonic motion
periodic motion in which the restoring force is proportional to the displacement of the oscillating object, and this force is directed toward the point of equilibrium
sine
the ratio of the opposite side of an angle in a right triangle to its hypotenuse
sliding (or kinetic) friction
resistive force between two surfaces that are moving relative to each other
slope
on a graph, the ratio of the vertical separation (rise) to the horizontal separation (run)
solid
state of matter with fixed volume and shape
special relativity
theory that describes how mass, length, and time are related, and the equivalence of matter and energy
specific heat capacity
the quantity of heat required to raise the temperature of one gram of water by one degree Celsius
spectrum
the range of electromagnetic waves from low frequency to high frequency, or colors when white light is passed through a prism
speed
the ratio of distance to time
speed of light
3 × 108 m/s in a vacuum; represented by the constant c
standing wave
wave with stationary nodes produced by two identical waves traveling in opposite directions in the same medium at the same time
static friction
the resistive force that opposes the start of motion between two surfaces in contact
strong nuclear force
the force that binds protons and neutrons together in the nucleus of an atom
superconductor
material that has practically no resistance to the flow of current at low temperatures
symmetry
property that is not changed when the reference frame is changed
system
defined collection of objects
tangent
touching at only one point on a curve; in a right triangle, the ratio of the opposite side to an adjacent side for either of the acute angles
tangential velocity
the velocity tangent to the path of an object moving in a curved path
temperature
the property of a body that indicates how hot or cold a substance is with respect to a standard, or a measure of the average internal kinetic energies of the molecules in an object
terminal velocity
the constant velocity of a falling object when the force of air resistance equals the object’s weight
test charge
the very small charge used to test the strength of an electric field
thermal energy
the sum of the internal potential and kinetic energies of the random motion of the molecules making up an object
thermal equilibrium
state between two or more objects or systems in which temperature doesn’t vary
thermal expansion
increase in length or volume of a material due to an increase in temperature
thermodynamics
the study of heat transfer
torque
the tendency of a force to cause rotation about an axis; the product of the force and the lever arm length
total internal reflection
the complete reflection of light that strikes the boundary between two media at an angle greater than the critical angle
trajectory
the path followed by a projectile
transformer
device that uses electromagnetic induction to transfer energy from one circuit to another
translucent
a material that passes light but distorts its path
transparent
material through which light can pass without distorting the direction of the rays
transverse wave
a wave in which the vibration is perpendicular to the velocity of the wave
trigonometry
the study of the relationships among the angles and sides of triangles
trough of a wave
the low point of wave motion
ultraviolet
electromagnetic waves of frequencies higher than those of violet light
uniform acceleration
constant acceleration
uniform circular motion
motion in a circular path of constant radius at a constant speed
uniform velocity
constant velocity
vector quantity
a quantity, such as displacement, having both magnitude and direction
velocity
ratio of the displacement of an object to a time interval
velocity-time graph
plot of the velocity of an object as a function of time, the slope of which is acceleration
virtual image
an image that cannot be projected onto a screen; point at which diverging light rays appear to originate
volt
the SI unit of potential or potential difference
voltage
amount of electric potential or potential difference
watt
the SI unit for power equal to one joule of energy per second
wavelength
the distance between successive identical parts of a wave
weight
the result of a gravitational force acting on a mass; the product of mass and the acceleration due to gravity at a location
weightlessness
the state of free fall where an object experiences only the force of gravity
white light
visible light consisting of all colors
work
the scalar product of force and displacement
work-energy theorem
the work done on a system is equal to the change in energy of the system
work function
the minimum energy required to release an electron from a metal
X-ray
high-frequency, high-energy electromagnetic waves or photons