M–P
M
- Magnetic flux
- The
dot product of the area and the magnetic field passing through it. Graphically,
it is a measure of the number and length of magnetic field lines
passing through that area. It is measured in Webers (Wb).
- Magnification
- The
ratio of the size of the image produced by a mirror or lens to the
size of the original object. This number is negative if the image
is upside-down.
- Magnitude
- A
property common to both vectors and scalars. In the graphical representation
of a vector, the vector’s magnitude is equal to the length of the
arrow.
- Margin of error
- The
amount of error that’s possible in a given measurement.
- Mass
- A measurement
of a body’s inertia, or resistance to being accelerated.
- Mass defect
- The
mass difference between a nucleus and the sum of the masses of the
constituent protons and neutrons.
- Mass number
- The
mass number, A, is the sum of the
number of protons and neutrons in a nucleus. It is very close to
the weight of that nucleus in atomic mass units.
- Maxima
- In an
interference or diffraction pattern, the places where there is the
most light.
- Mechanical energy
- The
sum of a system’s potential and kinetic energy. In many systems, including
projectiles, pulleys, pendulums, and motion on frictionless surfaces,
mechanical energy is conserved. One important type of problem in
which mechanical energy is not conserved is the class of problems
involving friction.
- Medium
- The
substance that is displaced as a wave propagates through it. Air
is the medium for sound waves, the string is the medium of transverse
waves on a string, and water is the medium for ocean waves. Note
that even if the waves in a given medium travel great distances,
the medium itself remains more or less in the same place.
- Melting point
- The
temperature at which a material will change phase from solid to
liquid or liquid to solid.
- Meson
- A class
of elementary particle whose mass is between that of a proton and
that of an electron. A common kind of meson is the pion.
- Michelson-Morley experiment
-
An experiment in 1879 that showed that the speed of
light is constant to all observers. Einstein used the results of
this experiment as support for his theory of special relativity.
- Minima
- In an
interference or diffraction pattern, the places where there is the
least light.
- Mole
- The number
of hydrogen atoms in one gram of hydrogen, equal to
 . When counting the number of molecules
in a gas, it is often convenient to count them in moles.
- Moment of inertia
- A
rigid body’s resistance to being rotated. The moment of inertia
for a single particle is MR2,
where M is the mass of the rigid body
and R is the distance to the rotation axis.
For rigid bodies, calculating the moment of inertia is more complicated,
but it generally takes the form of a constant multiplied by MR2.
- Momentum
- Linear
momentum, p, commonly
called “momentum” for short, is a vector quantity defined as the
product of an object’s mass, m, and
its velocity, v.
- Motional emf
- The
emf created by the motion of a charge through a magnetic field.
- Mutual Induction
- The
property by which a changing current in one coil of wire induces
an emf in another.
N
- Neutrino
- An
almost massless particle of neutral charge that is released along
with a beta particle in beta decay.
- Neutron
- A neutrally
charged particle that, along with protons, constitutes the nucleus
of an atom.
- Neutron number
- The
number, N, of neutrons in an atomic nucleus.
- Newton
- A unit
of force: 1 N is equivalent to a 1 kg · m/s2.
- Newton’s First
Law
- An object at rest remains at rest,
unless acted upon by a net force. An object in motion remains in
motion, unless acted upon by a net force.
- Newton’s Law of Universal Gravitation
-
The force of gravity, F,
between two particles of mass
 and  , separated by a distance r,
has a magnitude of  , where G is
the gravitational constant. The force is directed along the line
joining the two particles.
- Newton’s Second Law
-
F = ma.
The net force, F, acting
on an object causes the object to accelerate, a.
The magnitude of the acceleration is directly proportional to the
net force on the object and inversely proportional to the mass, m,
of the object.
- Newton’s Third Law
-
To every action, there is an equal and opposite reaction.
If an object A exerts a force on another
object B, B will
exert on A a force equal in magnitude
and opposite in direction to the force exerted by A.
- Node
- The points
on a standing wave where total destructive interference causes the
medium to remain fixed at its equilibrium position.
- Normal
- The
line perpendicular to a surface. There is only one normal for any
given surface.
- Normal force
- The
reaction force of the ground, a table, etc., when an object is placed
upon it. The normal force is a direct consequence of Newton’s Third
Law: when an object is placed on the ground, the ground pushes back
with the same force that it is pushed upon. As a result, the net
force of an object on the ground is zero, and the object does not
move.
- Nuclear fission
- A
nuclear reaction in which a high-energy neutron bombards a heavy,
unstable atomic nucleus, causing it to split into two smaller nuclei,
and releasing some neutrons and a vast amount of energy at the same
time.
- Nuclear fusion
- A
nuclear reaction that takes place only at very high temperatures.
Two light atoms, often hydrogen, fuse together to form a larger
single atom, releasing a vast amount of energy in the process.
- Nucleus
- The
center of an atom, where the protons and neutrons reside. Electrons
then orbit this nucleus.
O
- Optics
- The
study of the properties of visible light, i.e., the portion of the
electromagnetic spectrum with wavelengths between 360 and 780 nm
(1 nm =
 m/s).
- Orbit
- When
an object is held in circular motion about a massive body, like
a planet or a sun, due to the force of gravity, that object is said
to be in orbit. Objects in orbit are in perpetual free fall, and
so are therefore weightless.
- Oscillation
- A
back-and-forth movement about an equilibrium position. Springs,
pendulums, and other oscillators experience harmonic motion.
P
- Pascals
- The
unit for measuring pressure. One Pascal is equal to one Newton per
meter squared, 1 Pa = 1 N/m2.
- Pendulum
- A
pendulum consists of a bob connected to a rod or rope. At small
angles, a pendulum’s motion approximates simple harmonic motion
as it swings back and forth without friction.
- Period
- The
time it takes a system to pass through one cycle of its repetitive
motion. The period, T, is the inverse
of the motion’s frequency, f = 1/T.
- Phase
- Two oscillators
that have the same frequency and amplitude, but reach their maximum displacements
at different times, are said to have different phases. Similarly,
two waves are in phase if their crests and troughs line up exactly,
and they are out of phase if the crests of one wave line up with
the troughs of the other.
- Phase change
- When
a solid, liquid, or gas changes into another phase of matter.
- Photoelectric effect
-
When electromagnetic radiation shines upon a metal,
the surface of the metal releases energized electrons. The way in
which these electrons are released contradicts classical theories
of electromagnetic radiation and supports the quantum view according
to which electromagnetic waves are treated as particles.
- Photoelectron
- The
name of an electron released from the surface of a metal due to
the photoelectric effect.
- Photon
- A small
particle-like bundle of electromagnetic radiation.
- Pitch
- Another
word for the frequency of a sound wave.
- Planck’s constant
- A
constant,
 J · s, which is useful in quantum physics.
A second constant associated with Planck’s constant is  .
- Polarization
- A
process that aligns a wave of light to oscillate in one dimension
rather than two.
- Potential energy
- Energy
associated with an object’s position in space, or configuration
in relation to other objects. This is a latent form of energy, where
the amount of potential energy reflects the amount of energy that
potentially could be released as kinetic energy or energy of some
other form.
- Power
- Defined
as the rate at which work is done, or the rate at which energy is
transformed. P is measured in joules per second
(J/s), or watts (W).
- Pressure
- A
measure of force per unit area. Pressure is measured in N/m2 or
Pa.
- Principal axis
- The
straight line that runs through the focal point and the vertex of
a mirror or lens.
- Proton
- A positively
charged particle that, along with the neutron, occupies the nucleus
of the atom.
- Pulley
- A pulley
is a simple machine that consists of a rope that slides around a
disk or block.
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