I–L
I
- Ideal gas law
- An
equation, PV = nRT, that relates the
pressure, volume, temperature, and quantity of an ideal gas. An
ideal gas is one that obeys the approximations laid out in the kinetic
theory of gases.
- Impulse
- A vector
quantity defined as the product of the force acting on a body multiplied
by the time interval over which the force is exerted.
- Incident ray
- When
dealing with reflection or refraction, the incident ray is the ray
of light before it strikes the reflecting or refracting surface.
- Inclined plane
- A
wedge or a slide. The dynamics of objects sliding down inclined
planes is a popular topic on SAT II Physics.
- Index of refraction
-
The index of refraction n = c/v of
a substance characterizes the speed of light in that substance, v.
It also characterizes, by way of Snell's Law, the angle at which
light refracts in that substance.
- Induced current
- The
current induced in a circuit by a change in magnetic flux.
- Inelastic collision
-
A collision in which momentum is conserved but kinetic
energy is not.
- Inertia
- The
tendency of an object to remain at a constant velocity, or its resistance
to being accelerated. Newton’s First Law is alternatively called
the Law of Inertia because it describes this tendency.
- Inertial reference frame
-
A reference frame in which Newton’s First Law is true.
Two inertial reference frames move at a constant velocity relative
to one another. According to the first postulate of Einstein’s theory
of special relativity, the laws of physics are the same in all inertial
reference frames.
- Instantaneous velocity
-
The velocity at any given instant in time. To be contrasted
with average velocity, which is a measure of the change in displacement
over a given time interval.
- Internal energy
- The
energy stored in a thermodynamic system.
- Inversely proportional
-
Two quantities are inversely proportional if an increase
in one results in a proportional decrease in the other, and a decrease
in one results in a proportional increase in the other. In a formula
defining a certain quantity, those quantities to which it's inversely proportional
will appear in the denominator.
- Isolated system
- A
system that no external net force acts upon. Objects within the
system may exert forces upon one another, but they cannot receive
any impulse from outside forces. Momentum is conserved in isolated
systems.
- Isotope
- Atoms
of the same element may have different numbers of neutrons and therefore different
masses. Atoms of the same element but with different numbers of
neutrons are called isotopes of the same element.
J
- Joule
- The joule
(J) is the unit of work and energy. A joule is 1 N
· m or 1 kg · m2/s2.
K
- Kelvin
- A scale
for measuring temperature, defined such that 0K is
the lowest theoretical temperature a material can have. 273K
= 0ºC.
- Kepler’s First Law
-
The path of each planet around the sun is an ellipse
with the sun at one focus.
- Kepler’s Second Law
-
If a line is drawn from the sun to the planet, then
the area swept out by this line in a given time interval is constant.
- Kepler’s Third Law
-
Given the period, T, and
semimajor axis, a, of a planet’s orbit,
the ratio
 is the same for every planet.
- Kinematic equations
-
The five equations used to solve problems in kinematics
in one dimension with uniform acceleration.
- Kinematics
- Kinematics
is the study and description of the motion of objects.
- Kinetic energy
- Energy
associated with the state of motion. The translational kinetic energy
of an object is given by the equation
 .
- Kinetic friction
- The
force between two surfaces moving relative to one another. The frictional force
is parallel to the plane of contact between the two objects and
in the opposite direction of the sliding object’s motion.
- Kinetic theory of gases
-
A rough approximation of how gases work, that is quite
accurate in everyday conditions. According to the kinetic theory,
gases are made up of tiny, round molecules that move about in accordance
with Newton’s Laws, and collide with one another and other objects
elastically. We can derive the ideal gas law from the kinetic theory.
L
- Latent heat of fusion
-
The amount of heat necessary to transform a solid at
a given temperature into a liquid of the same temperature, or the
amount of heat needed to be removed from a liquid of a given temperature
to transform it into a solid of the same temperature.
- Latent heat of sublimation
-
The amount of heat necessary for a material undergoing
sublimation to make a phase change from gas to solid or solid to
gas, without a change in temperature.
- Latent heat of transformation
-
The amount heat necessary to cause a substance to undergo
a phase transition.
- Latent heat of vaporization
-
The amount of heat necessary to transform a liquid at
a given temperature into a gas of the same temperature, or the amount
of heat needed to be taken away from a gas of a given temperature
to transform it into a liquid of the same temperature.
- Law of conservation of energy
-
Energy cannot be made or destroyed; energy can only
be changed from one place to another or from one form to another.
- Law of reflection
- For
a reflected light ray,
 . In other words, a ray
of light reflects of a surface in the same plane as the incident
ray and the normal, and at an angle to the normal that is equal
to the angle between the incident ray and the normal.
- Legs
- The two
shorter sides of a right triangle that meet at the right angle.
- Lenz’s Law
- States
that the current induced in a circuit by a change in magnetic flux
is in the direction that will oppose that change in flux. Using
the right-hand rule, point your thumb in the opposite direction
of the change in magnetic flux. The direction your fingers curl
into a fist indicates the direction of the current.
- Longitudinal waves
-
Waves that oscillate in the same direction as the propagation
of the wave. Sound is carried by longitudinal waves, since the air
molecules move back and forth in the same direction the sound travels.
- Loudness
- The
square of the amplitude of a sound wave is called the sound’s loudness,
or volume.
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