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Glossary Quick Link


absolute zero Lowest possible temperature at which gas would have zero volume.
absorbed dose Describes how much energy is deposited by a source per kilogram of exposed tissue. Its SI unit is the gray (Gy) and a common non-SI unit is Rads. 1 Gy = 1 J/kg = 100 Rads The radiation for the treatment of cancer generally involves an absorbed dose of 40 Gy.
acceleration Change in velocity divided by time interval over which it occurred.
activity Number of decays per second of a radioactive substance.
air resistance Force of air on objects moving through it.
alpha particle Positively-charged particles consisting of two protons and two neutrons emitted by radioactive materials. Are positively charged particles emitted from alpha decay. These particles are helium nuclei.
ammeter device to measure electrical current.
annihilation Process in which a particle and its antiparticle are converted into energy.
antenna Device used to receive or transmit electromagnetic waves.
antineutrino Subatomic particle with no charge or mass emitted in beta decay.
Applied Force
A push or a pull that is applied to an object. The unit for force is the Newton (N). It is a vector quantity and therefore requires direction.
artificial radioactivity Radioactive isotope not found in nature.
atomic mass unit (u) Unit of mass equal to 1/12 the atomic mass of the carbon-12 nucleus.
atomic number (Z) Number of protons in the nucleus of the atom.
average acceleration Acceleration measured over a finite time interval.
average speed Is the total distance traveled divided by the change in time.
average velocity Velocity measured over a finite time interval. The slope of the line is a ratio of the rise to the run. The change y over the change over x.


Base Level Is an arbitrary reference point from an object\'s vertical position may be calculated. This change in height relative to the reference point may then be used to calculate gravitational potential energy.
becquerel (Bq) Measures the activity of a source. One becquerel is equal to one emission per second. 1 Bq = 1 emission per second = 1 Curie (Ci)
beta particles Are electrons that are emitted from beta decay. For an electron, the subscript represents the charge and not, as in most cases, the number of protons.


Calandria This is another word for Reactor Vessel. It contains the pressure tubes and the moderator.
CANDU reactor Canadian Deuterium Uranium Reactor is one of the safest fission reactors in the world. It was developed by members of the AECL (Atomic Energy of Canada Limited).
Centripetal Acceleration Acceleration toward the center of circular motion. The units are m/s2
Chain Reaction A nuclear reaction where the neutrons produced during a reaction causes a chain of similar reactions. A controlled chain reaction occurs in a nuclear reactor whereas in an atomic bomb an uncontrolled chain reaction occurs.
Chassis Ground A chassis ground or a ground may be a common plane of zero voltage compared with the rest of the circuit.
collinear vectors Are vectors that are in the same direction or the exact opposite direction. They exist in only one dimension.
Condensers Change the steam in a nuclear reactor back into water so that it can be cycled back into the steam generator.
Conservation of Momentum The total momentum of a system does not change.

initial momentum = final momentum

This is one of the most fundamental principles in physics.

constant acceleration occurs when the objects velocity changes by equal amounts in equal periods of time.
constant speed occurs when the object travels the same distance in equal periods of time. The SI unit is the meter per second (m/s).
constant velocity occurs occurs when the object has the same displacement in equal periods of time.
Control Rods Are used to control the rate of a chain reaction by capturing neutrons. They are often made of boron or cadmium and are inserted into the moderator and fuel to reduce the rate of fission.
Coolant The coolant used in the CANDU reactor is heavy water. It flows through the pressure tubes in the calandria and transfers the heat from the fuel to ordinary water through a heat exchanger. This ordinary water produces steam, which will turn turbines to generate electricity.
Critical Mass Is the minimum mass of fissionable material that will produce a nuclear explosion. If the amount of U-235 is to small, the neutrons produced during fission will be less than the number of neutrons that will escape from the surface of the mass.( i.e. no sustained chain reaction)
Current is the rate of flow of charge passing through a cross-sectional area in a conductor. It is considered to be a flow of positive charge.


dependent variable A mathematical variable whose value is determined by the value assumed by an independent variable. This value is plotted on the y-axis.
Deuterium Is an isotope of hydrogen that has one neutron in the nucleus,Deuterium.
displacement  (Displacement vector symbol.) Is the change in position of an object. It is the straight line segment that connects the initial and final positions. Displacement is a vector quantity and therefore needs to be described with a magnitude and a direction. The SI unit is the meter.
distance (Distance symbol) Is the length of the path traveled by an object as it moves from one point to another. It is a scalar quantity and therefore only needs to be described using a magnitude. The SI unit is the meter.
dose equivalent Measures the biological damage produced on an organism. Its SI unit is the sievert (Sv). Dose equivalent (Sv) = absorbed dose (Gy) quality factor (Q).
dosimetry Is the measurement of radiation and the study of its effects on living organisms.
Dot Interval The space between the dots on a recording tape.
Dynamics The branch of physics that examines the description of motion and the forces behind the motion.


Elastic Collision Is one in which there is no change in kinetic energy after the collision has occurred. Kinetic energy is conserved.
Electric Field An electric field is a region in space where a force is exerted on a positive test charge.
Electric Lines of Force Electric lines of force represent the direction that a positive test charge would move in an electric field. By convention, they originate at positively charged objects and terminate at negatively charged objects.
Electric Potential Difference The electric potential difference (V) is the work done per unit charge as a charge is moved between two points in an electric field.
Energy (E) Is the ability to do work. When work is done, energy is transferred from one object to another. The unit for energy is the Joule.
Enrichment The process of increasing the percentage of uranium-235 in a natural uranium ore so that a chain reaction will be sustained.
Equivalent Displacements Are displacements that have the same magnitude and direction. Equivalent displacements do not need to have the same origin.
Equivalent Vectors Are vectors with the same magnitude and direction.
Equivalent (total) Resistance This resistance can be considered to consist of a single resistance, which replaces two or more resistances.


Fission Results when a slow moving neutron is absorbed by a heavy nucleus causing it to split into smaller nuclei.
force Force causes an object to change shape or accelerate. The SI units are ..
force of gravity The force which is caused by the attraction between two objects due to their mass.
FBD FBD - Free Body Diagram. A diagram which has all of the external forces labeled on the object. Usually, Force Applied - Fa, Normal Force - FN, Force of Friction (either static or kinetic), Force of Gravity - Fg, and any angles.
Frequency (f) The number of vibrations per unit time. One vibration per second is called one hertz (Hz).
friction force The force which acts between the surfaces of two objects in contact.
Fuel bundles Contain cylindrical rods made up of uranium oxide fuel pellets. These fuel bundles are placed in special pressure tubes inside the calandria.


Galileo's Thought Experiement Galileo developed the concept of inertia.
Gamma rays Are usually emitted along with alpha and beta decay. Gamma rays are electromagnetic radiation ( a form of light) that produces no change in the atomic mass or atomic number of the radioactive nucleus. The symbol used for gamma rays is .
Graphing A diagram that exhibits a relationship, often functional, between two sets of numbers as a set of points having coordinates determined by the relationship.
Gravitational Potential Energy Is the energy stored as a result of the vertical position (height) of an object. It\'s position may be relative to the ground level or a base level. It may be calculated using

Eg = mgh

where Eg = gravitational potential energy (J)

m = mass of the object (kg)

g = 9.80 m/s2h = change in height relative to the reference point (m)

Gravity At a given location on the Earth and in the absence of air resistance all object fall with the same constant acceleration. g = 9.80 m/s2.
Ground Level Is the surface of the earth or the floor of any room from an object\'s vertical position may be calculated. This change in height relative to the reference point may then be used to calculate gravitational potential energy.


Heavy water The chemical symbol for heavy water is D2O. It contains deuterium which is an isotope of hydrogen. It is used as the moderator and the coolant in the CANDU reactor.
horsepower One horsepower is equal to 746 joules/second (746 W). The unit horsepower was used to describe the output of a workhorse.


independent variable A variable whose value determines the value of other variables (dependent variable). This value is plotted on the x-axis.
Inelastic Collision Is one where some energy is "lost" when colliding objects are in contact. This "lost" or dissipated energy usually results in the production of heat. It may also produce sound, light, or other forms of energy.
inertia a property of matter by which it remains at rest or in uniform motion in the same straight line unless acted upon by some external force.
instantaneous acceleration is the acceleration of an object at a specific time.
instantaneous speed is the speed at a specific instant in time. The SI unit is the meter per second (m/s).
instantaneous velocity is the instantaneous speed in a specific direction.
isotopes Are elements that have the same atomic number but different atomic masses due to a change in its number of neutrons.



Kinematics The branch of physics that involves the description of motion without examining the forces which produce the motion.
Kinetic Energy Is the energy of motion. It can be calculated by

Ek = kinetic energy (J)
m = mass (kg)
v = velocity or speed (m/s)
Gustav Robert Kirchhoff Born: 12 March 1824 in Königsberg, Prussia (now Kaliningrad, Russia)
Died: 17 Oct 1887 in Berlin, Germany

Kirchhoff's laws, which he announced in 1845, allowed calculation of currents, voltages and resistances in electrical circuits with multiple loops, extending the work of Ohm. Kirchhoff considered an electrical network consisting of circuits joined at nodes of the network and gave laws which reduce the calculation of the currents in each loop to the solution of algebraic equations.

Kirchhoff's Current Law At any junction in an electric circuit, the total current flowing into the junction is the same as the total current leaving the junction.
Kirchhoff's Voltage Law The algebraic sum of the potential difference around any closed path or loop must be zero.



mass SI units for mass are kilograms. Mass is a scalar quantitiy which does depend on gravity - the mass of an object is 60 kg on the Earth, on the Moon, on any planet. Mass and weight are different.
Moderator Is a substance that is used to slow down the neutrons in nuclear reactors. Some common moderators are: graphite, heavy water, and beryllium.
momentum The product of a object's mass and velocity.
motion The movement of an object, or change in place.
µ µ (mu) called the coefficient of friction is a constant. µk is used when the object is in motion (kinetic), and µs (mu) called the coefficient of friction is a constant. µs is used when the object is at rest (static)


Negative work Is done when the applied force and the displacement act in opposite directions.
non-collinear vectors Are vectors that exist in more than one dimension.
non-uniform motion Is motion where the direction and/or the speed of the object can change. Non-uniform motion has a change in velocity which has a special name called acceleration.
normal force The force which acts perpendicular to the plane at which the object rests.
Nuclear Fuel Cycle The entire cycle from mining the fuel to its disposal after use.
Nuclear Mass Defect Is the difference between the masses of the parent atom and the slow moving neutron and the masses of the daughter atoms with the emitted neutrons. It can be used to determine the energy released during fission. E=mc2

where E = energy released
c = speed of light = 300 000 000 m/s
m= nuclear mass defect

Nuclear Reactor It is a device where a controlled chain reaction occurs. The energy released from this reaction is used to drive turbines, which generate electricity.



Parallel Circuit In this circuit, electrons can flow along one or more pathways (i.e. alternate paths for current to follow).
period (T) Is the length of time required for one vibration. A period is usually expressed in seconds.
physical quantity A quantity that can be measured.
Physics The branch of science that studies the physical world.
power Is the rate at which work is done. It is a scalar quantity with SI units of watts (W). Another commonly used unit is the horsepower.

Since work done is approximately equal to the energy used, W = ~E, power can also be described as the rate at which energy is used.

position (Position vector symbol.) The location of an object relative to a reference point. It is a vector quantity and as such needs a magnitude and direction. The SI unit is the meter.
Positive work Is done when the applied force and the displacement act in the same direction.
Potential Energy energy of rest.
Projectiles Motion of an object with an inital velocity which is acted upon by only one force, the force of gravity.


Quality factor A number assigned to each type of radiation to describe its biological effects. It was defined by comparing its effects with those of a standard radiation of 200 keV X-rays. Quality factors are approximate since they depend on the energy of the radiation and the type of tissue being irradiated. Note: a keV is a kiloelectronvolt


radioactivity Is the spontaneous breakdown of an atom and results in the emission of particles or electromagnetic radiation.
reference point Is the zero or initial location of an object.
Resistance Resistance is anything that causes an opposition to the flow of electricity in a circuit. It is used to control the amount of voltage and/or amperage in a circuit. Everything in the circuit causes a resistance (even wire). It is measured in OHMS ()
Resistivity the longitudinal electrical resistance of a uniform rod of unit length and unit cross-sectional area : the reciprocal of conductivity. Resistance depends on the resistivity of the material. The resistivity is defined as the resistance of a cylinder of the material 1 meter long with a cross-sectional area of 1 m2. Resistivity varies with temperature. It is measured in ohms m2/m. (Some texts use ohm m.)
resultant vector Is the sum of two or more vectors.


scalar quantity A quantity that can be described completely with a magnitude. The magnitude is made up of both a number and a unit. Some examples are mass, time, distance, speed, and work.
Series Circuit In this circuit, electrons can flow along one path only.
slope the slope of the line is a ratio of the rise to the run. The change y over the change over x.
speed-average(vav) Is the total distance traveled divided by the change in time.
Stroboscope An instrument that allows you to see frames of movement and is therefore useful when examining rapid motion.
Superconductivity a complete disappearance of electrical resistance in a substance especially at very low temperatures.


Tailings The waste material from the uranium ore after the uranium has been extracted. This material is slightly radioactive and must be disposed of with care.
Total Mechnaical Energy Is the sum of the kinetic and gravitational potential energy in an object. ET = Eg + Ek


Uniform motion Is the simplest form of motion. It can be defined as motion in a straight line, in a specific direction at a constant speed. It can also be described as motion with a constant velocity.


vector Is a vector quantity that is represented on a diagram by a line segment with an arrow at one end to indicate direction. Reference coordinates must also be included. The tail of the vector is at its origin and the tip is at the terminal point (the arrow). The length of the vector, drawn to scale, represents its magnitude. Vector Diagram
vector quantity A quantity that consists of both magnitude and direction. The magnitude is made up of both a number and a unit. Some examples are position, displacement, velocity, acceleration, force, and weight.
vector resolution Resolving vectors into vector components along the x and y-axes.
velocity Velocity is defined as the displacement of an object divided by the time elapsed. Velocity is usually classified as Average,, Constant, or Instantaneous. The SI units are m/s.
vibration One complete to and fro motion.
Voltage electric potential or potential difference expressed in volts. Also known as electromotive force - it is the force that pushes and pulls electrons through a conductor.


Weight The force of gravity on an object.
Work (W) Is a scalar quantity. It is the product of an applied force and the displacement of an object in the direction of the applied force. The unit for work is a newton.meter (N.m) which equals a Joule (J).




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