Physics Glossary


applied force - The push or pull of a human or machine.

average acceleration -- The slope of the velocity-time graph, or a_avg = (delta v/delta t).  This is a way to find average acceleration over any time interval.

average velocity -- For constant velocity, it is the slope of the position-time graph. Mathematical definition is v_avg=(delta x)/(delta t). This is a way to find average velocity over any time interval.

amplitude--The distance from some central reference point, without regard to direction.  The side-to-side angle of a pendulum's swing, or the height of wave crests (and depth of the troughs).


clock reading -- How you would determine an instant in time, by glancing at the timekeeper and recording what it shows at that moment.

constant -- Any physical quantity that maintains the same value over a time interval. In a lab, something that you try to keep from changing during data collection.

curve -- A function that is graphed, may actually be curved or it may be linear.

component vector -- a quantity we calculate to represent what portion of a vector is purely horizontal (X-component) or purely vertical (Y-component).

conservation/conserved -- If a physical quantity in a closed system has the same value both before and after a process, that quantity is said to be conserved. Examples may include: mass, energy, linear momentum, angular momentum, charge.


delta -- Greek letter (looks like a triangle) that represents change in a physical quantity. For example, "delta X" is (X - X_0; OR X_2 - X_1; OR X_final - X_initial)

displacement -- Change in position (delta x or xf - xi). Displacement is a vector that has magnitude and direction. If we are considering a change in position in one dimension only, the direction is denoted by whether the displacement is positive or negative. If the change is in two dimensions (or more), we specify an angle relative to our Cartesian coordinate system.

directly proportional -- Two variables that have a linear relationship.


energy -- The agent of change in the universe. Modeled as a somewhat mysterious thing that behaves like an invisible, undetectable substance. It can be stored in many places. For any closed system (nothing can enter or leave), energy is conserved (the total amount is constant). 


force - One end of the interaction between two objects.

friction - a contact force that opposes the tendency to relative motion. See sliding friction, rolling friction, drag.

frequency - The number of cycles per second of a process that repeats. Symbolized by an f  and measured in Hertz (Hz) or 1/s.  Equivalent to 1/T.


inertia -- The tendency of matter to "hold back" when you try to make it move and the tendency of matter to "keep going" in the direction it is moving.

instantaneous velocity -- The velocity at any single clock reading. The slope of a line tangent to a point on a position-time graph.

inversely proportional -- Two variables that have an inverse relationship (y=k/x).


length -- What you measure with a ruler, meter stick, or tape measure.

linearization -- The process of performing a mathematical operation on a list of data in order to make a non-linear graph into a linear function.  See the Graphical Analysis page for more information.


magnitude -- The size of something (a physical quantity, like velocity), without regard to its other characteristics (direction, for instance).

mass-- Inertia quantified. A quality of mass that tends to resist changes in motion. What a balance measures.

mechanism -- The way we describe how something happens.  "Force is the mechanism for energy transfer."

medium -- The material through which a wave is propagated. May be a liquid, solid, or gas, as in mechanical waves, or it may be space itself, as in electromagnetic waves.

model -- A representation of an object, system, or concept that has some of the characteristics of the actual object, system, or concept. Constructed b/c it can make predictions about the actual thing, communicate meaning, or be used to test ideas. Often we make models when the real thing is unavailable, difficult to work with, or we are looking for a shorthand way to communicate about something.

momentum -- Another physics quantity that is conserved in a closed system. A vector quantity that is the product of mass and velocity.


operational definition -- Many physical quantities don't exist as things, but only when a human performs a certain operation to measure them. For example, area is defined by the process of finding out how many unit squares (1 meter on a side, for example) fit into a two-dimensional shape.


paradigm -- A pattern. An example that can be used for comparison.

period - the time for one complete cycle of a process that repeats. Symbolized by a T. Measured in seconds (s) and equivalent to 1/f.

position -- The distance and direction (typically given as negative or positive) from a reference point.

proportionality -- Any two variables that change in a constant ration have a relationship that may be described as being proportional. Any two variables that produce a linear graph (y=mx or y=mx+b) are proportional.


quantity -- Something that can be measured that conveys information about a physical system.  Examples: length, mass, time.


reference point -- A point in space designated as zero for measurements of position.

representation -- Words, equations, graphs, or pictures intended to communicate essential information about a model.


scalar -- Anything you might measure that can be designated by a single number. Physical quantities without direction. Examples: time, temperature, mass.

speed -- Total distance/total time. A scalar. Answer to the question "How fast?"

symmetry -- Something that can be folded across one or more axes (or lines) and what is folded on itself matches up. The human body is roughly "symmetric," meaning the right side is almost exactly the same as the left side.

system - Any object or objects that you are interested in.  If there are multiple objects, then these objects interact in some way.


test plot -- This is the graph produced when you "try out" a mathematical operation to linearize data that plots as a curve.  If the test plot is successful, then it will be linear. 

time -- What a clock measures.

time interval -- Delta t, or change in time (t2 - t1).

trajectory - The path of an object moving through space, usually dealt with in this class by a representation (a graph, picture, or motion map).


unit -- The standardized system for measuring a physical quantity.  "Standard" means people agree upon what is the basic amount.  For instance, the kilogram is the unit of mass, and in Paris, there is a chunk of metal that everybody agrees has a mass of one kilogram.  Examples: for length, meters or feet, for time seconds or minutes.

uncertainty -- For this class, an estimate of the amount of variation in a measurement. Since all honest measurements vary due to circumstances beyond the scientists' control, there is always some uncertainty. See for more info.


variable -- A symbol that stands for a physical quantity.  Examples: m for mass, x for horizontal length, y for  a vertical length, t  for a time.

vector -- A physical quantity with magnitude (size) and direction.


wave -- A disturbance in a medium that transmits energy and momentum through coupled oscillations.

work(ing) -- Energy transferred into or out of a system.

By Marc Reif - Any errors or omissions are my fault.  Please let me know so I can correct them.