Q–T
Q
- Quark
- The building
blocks of all matter, quarks are the constituent parts of protons,
neutrons, and mesons.
R
- Radian
- A unit
for measuring angles; also called a “rad.” 2π rad
= 360º.
- Radiation
- Heat
transfer via electromagnetic waves.
- Radioactive decay
- The
process by which unstable nuclei spontaneously release particles
and/or energy so as to come to a more stable arrangement. The most
common forms of radioactive decay are alpha decay, beta decay, and
gamma decay.
- Radioactivity
- An
object is called radioactive if it undergoes radioactive decay.
- Radius of curvature
-
With spherical mirrors, the radius of the sphere of
which the mirror is a part.
- Rarefaction
- An
area of high air pressure that acts as the wave trough for sound
waves. The spacing between successive rarefactions is the wavelength
of sound, and the number of successive areas of rarefaction that
arrive at the ear per second is the frequency, or pitch, of the
sound.
- Real image
- An
image created by a mirror or lens in such a way that light does
actually come from where the image appears to be. If you place a
screen in front of a real image, the image will be projected onto
the screen.
- Reflect
- A wave
on a string that is tied to a pole at one end will reflect back
toward its source, producing a wave that is the mirror-image of
the original and which travels in the opposite direction.
- Reflected ray
- The
ray of light that is reflected from a mirror or other reflecting
surface.
- Reflection
- The
phenomenon of light bouncing off a surface, such as a mirror.
- Refracted ray
- The
ray of light that is refracted through a surface into a different
medium.
- Refraction
- The
bending of light as it passes from one medium to another. Light
refracts toward the normal when going from a less dense medium into
a denser medium and away from the normal when going from a denser
medium into a less dense medium.
- Restoring force
- The
force that causes simple harmonic motion. The restoring force is
always directed toward an object’s equilibrium position.
- Right-hand rule
- A
means of defining the direction of the cross product vector. To
define the direction of the vector
 , position your right hand so that your
fingers point in the direction of A,
and then curl them around so that they point in the direction of B.
The direction of your thumb shows the direction of the cross product
vector.
- Rigid body
- An
object that retains its overall shape, meaning that the particles
that make up the rigid body stay in the same position relative to
one another.
- Rotational kinetic energy
-
The energy of a particle rotating around an axis.
- Rotational motion
- Occurs
when every point in the rigid body moves in a circular path around
a line called the axis of rotation.
- Rutherford nuclear model
-
The model of the atom according to which negatively
charged electrons orbit a positively charged nucleus. This model
was developed by Ernest Rutherford in light of the results from
his gold foil experiment.
S
- Scalar
- A quantity
that possesses a magnitude but not a direction. Mass and length
are common examples.
- Second Law of Thermodynamics
-
There are a few versions of this law. One is that heat
flows spontaneously from hot to cold, but not in the reverse direction.
Another is that there is no such thing as a 100% efficient heat
engine. A third states that the entropy, or disorder, of a system
may increase but will never decrease spontaneously.
- Significant digits
-
The number of digits that have been accurately measured.
When combining several measurements in a formula, the resulting
calculation can only have as many significant digits as the measurement
that has the smallest number of significant digits.
- Simple harmonic oscillator
-
An object that moves about a stable equilibrium point
and experiences a restoring force that is directly proportional
to the oscillator’s displacement.
- Sine
- In a right
triangle, the sine of a given angle is the length of the side opposite
the angle divided by the length of the hypotenuse.
- Snell’s Law
- Relates
the angle of incidence to the angle of refraction:
 .
- Sound
- Waves
carried by variations in air pressure. The speed of sound waves
in air at room temperature and pressure is roughly 343 m/s.
- Specific heat
- The
amount of heat of a material required to raise the temperature of
either one kilogram or one gram of that material by one degree Celsius.
Different units may be used depending on whether specific heat is
measured in s of grams or kilograms, and joules or calories.
- Spectroscope
- A
device that breaks incoming light down into spectral rays, so that
one can see the exact wavelength constituents of the light.
- Speed
- A scalar
quantity that tells us how fast an object is moving. It measures
the rate of change in distance over time. Speed is to be contrasted
with velocity in that there is no direction associated with speed.
- Spring
- Objects
that experience oscillatory or simple harmonic motion when distorted.
Their motion is described by Hooke’s Law.
- Spring constant
- Indicates
how “bouncy” or “stiff” a spring is. More specifically, the spring constant, k,
is the constant of proportionality between the restoring force exerted
by the spring, and the spring’s displacement from equilibrium. The
greater the value of k, more resistant
the spring is to being displaced.
- Standing wave
- A
wave that interferes with its own reflection so as to produce oscillations
which stand still, rather than traveling down the length of the
medium. Standing waves on a string with both ends tied down make
up the harmonic series.
- Static friction
- The
force between two surfaces that are not moving relative to one another.
The force of static friction is parallel to the plane of contact
between the two objects and resists the force pushing or pulling
on the object.
- Strong nuclear force
-
The force that binds protons and neutrons together in
the atomic nucleus.
- Sublimation
- The
process by which a solid turns directly into gas, because it cannot
exist as a liquid at a certain pressure.
- Superposition
- The
principle by which the displacements from different waves traveling
in the same medium add up. Superposition is the basis for interference.
- System
- A body
or set of bodies that we choose to analyze as a group.
T
- Tail
- In the
graphical representation of vectors, the tail of the arrow is the
blunt end (the end without a point).
- Tangent
- In
a right triangle, the tangent of a given angle is the length of
the side opposite the angle divided by the length of the side adjacent
to the triangle.
- Temperature
- A
measure of the average kinetic energy of the molecules in a system.
Temperature is related to heat by the specific heat of a given substance.
- Tension force
- The
force transmitted along a rope or cable.
- Thermal energy
- The
energy of the molecules that make up an object. It is related to
heat, which is the amount of energy transferred from one object
to another object that is a different temperature.
- Thermal equilibrium
-
Two materials are in thermal equilibrium if they are
at the same temperature.
- Third Law of Thermodynamics
-
An object cannot be cooled to absolute zero.
- Threshold frequency
-
A property of a metal, the minimum frequency of electromagnetic radiation
that is necessary to release photoelectrons from that metal.
- Tip
- In the
graphical representation of vectors, the tip of the arrow is the
pointy end.
- Torque
- The
effect of force on rotational motion.
- Total internal reflection
-
The phenomenon by which light traveling from a high n to
a low n material will reflect from the optical
interface if the incident angle is greater than the critical angle.
- Transformer
- A
device made of two coils, which converts current of one voltage
into current of another voltage. In a step-up transformer, the primary
coil has fewer turns than the secondary, thus increasing the voltage.
In a step-down transformer, the secondary coil has fewer turns than
the primary, thus decreasing the voltage.
- Translational kinetic energy
-
The energy of a particle moving in space. It is defined
in s of a particle’s mass, m, and
velocity, v, as (1/2)mv2.
- Translational motion
-
The movement of a rigid body’s center of mass in space.
- Transverse waves
- Waves
in which the medium moves in the direction perpendicular to the propagation
of the wave. Waves on a stretched string, water waves, and electromagnetic waves
are all examples of transverse waves.
- Traveling waves
- A
wave with wave crests that propagate down the length of the medium,
in contrast to stationary standing waves. The velocity at which
a crest propagates is called the wave speed.
- Trough
- The
points of maximum negative displacement along a wave. They are the
opposite of wave crests.
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