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***aberration** The unavoidable distortion in an image produced by a lens.

***absolute value** The numerical value of a real number, with no positive or minus sign. Absolute values are written with neither +/-. They are treated as positive numbers since it is assumed that numbers without signs are positive. The absolute value of any nonzero, real number is a positive number. The absolute value of zero is zero.

***absolute zero** Lowest possible temperature at which gases have zero volume. (0 K on the Kelvin scale, -273.16°C on the Celsius scale, or -459.60°F on the Fahrenheit scale).

***acceleration ** Acceleration is the rate at which velocity is changing with time*. *The change can be either positive or negative*. *Negative changes in acceleration -- or slowing -- are sometimes called deceleration.

***acceleration due to gravity** The acceleration produced in a body due to the earth's gravitational attraction. It is denoted by the letter g. Its SI unit is m/s². On the surface of the earth, its average value is 9.8m/s².

***accuracy **Closeness of a measurement to the standard value.** **

**action force** The initial force referred to in Newtons third law of motion. **See also**: reaction force.

***activity** Number of decays per second of a radioactive substance.

***adhesion ** Force of attraction of unlike materials.

***air resistance **The friction that acts on something moving through air.

***alpha particle **The nucleus of a helium atom (two protons and two neutrons) emitted as radiation from a decaying heavy nucleus

***amplitude ** The distance from the midpoint to the crest of a wave, or from the midpoint to the trough.

***angular acceleration** The change in angular speed. The acceleration of an object in rotational motion, specified as revolutions, radians, or rotations per unit of time squared and symbolized as a . Angular acceleration is a vector quantity. Also referred to as rotational acceleration.

***angular momentum** The inertia of rotation; Angular momentum (*L*) is calculated by multiplying the moment of inertia (*I*) and the angular velocity (w ): ** L = Iw**.

***angular speed** The speed of an object in rotational motion, specified as revolutions, radians, or rotations per unit of time and symbolized as w. Angular speed is a scalar quantity. Also referred to as rotational speed.

***angular velocity** Angular speed with a directional counterpart. Angular velocity is a vector quantity. The direction of angular velocity is constantly changing and is generally described as clockwise or counterclockwise. Units of measure are rotations per time, as in rotations per minute (RPM). Also referred to as rotational velocity.

***Archimedes Principal ** Object immersed in a fluid has an upward force equal to the weight of the fluid dispalced by the object.

***average speed ** Average speed (v) or "overall speed" is calculated as the total distance traveled (s) divided by the amount of time (t) required to travel that distance

***atom **The smallest unit of an element that can exist alone or in combination with other elements.

***beat **Slow oscillation in amplitude of a complex wave.

***binding energy **The energy required to break a nucleus into its constituent protons and neutrons; also the energy equivalent released when a nucleus is formed.

***beta particle **High-energy electron emitted as ionizing radiation from a decaying nucleus.

***big bang theory **Current model of galactic evolution in which the universe was created from an intense and brilliant explosion from a primeval fireball.

***Bohr model **A simple model of the structure of the atom that attempted to correct the deficiencies of the solar system model and account for the Balmer series.

***British Thermal Unit **The amount of energy or heat needed to increase the temperature of one pound of water one degree Fahrenheit (abbreviated Btu).

***buoyant force ** A term for the net upward force exerted by a liquid or gas on an object that is immersed or submerged.

***calorie** A unit of heat that is the amount of energy required to raise the temperature of one gram of water one degree Celsius.

***center of gravity** The point at which all of an object's mass seems to be concentrated.

***centrifugal force ** The apparent outward force of a revolving body. It is a ictitious force.

***centripetal acceleration** Centripetal acceleration is acceleration that is directed toward the center of a circle. See: acceleration.

***centripetal force** The center-seeking force that makes an object move in a circular path.

***Circular Motion **The motion of a body along a circular path.

***Compression **A part of a longitudinal wave in which the density of the particles of the medium is higher than the normal density is called a compression.

***Conduction **The transfer of heat from a region of higher temperature to a region of lower temperature by increased kinetic energy moving from molecule to molecule. In electricity, the transfer of charge.

***Convection **Transfer of heat from a region of higher temperature to a region of lower temperature by the displacement of high-energy molecules-for example, the displacement of warmer, less dense air (higher kinetic energy) by cooler, denser air (lower kinetic energy).

***Coulomb **Unit used to measure quantity of electric charge; equivalent to the charge resulting from the transfer of 6.24 billion particles such as the electron

***Crest **The point of maximum positive displacement on a transverse wave is called a crest.

***critical angle**The minimum angle of incidence at which a light ray is totally reflected within a medium.

***De Broglie wavelength **Length of de Broglie wave of a particle; Planck's constant divided by momentum of a particle.

***deceleration** Deceleration is negative acceleration. Commonly referred to as "slowing down".

***density** is the amount of matter (mass) contained in a given space (volume); Mass divided by volume.

***diffraction **The bending of light around the edge of an opaque object.

***Dispersion **The effect of spreading colors of light into a spectrum with a material that has an index of refraction that varies with wavelength.

***diffraction **The bending of light around the edge of an opaque object.

***Doppler effect **An apparent shift in the frequency of sound or light due to relative motion between the source of the sound or light and the observer.

***dynamics** The science of why objects move.

***elastic collision** When colliding bodies rebound with no lasting deformation or generation of heat.

***elastic limit** This marks the end of the elastic region for a given material. Beyond this point, the material can no longer return to its original length once an applied force is removed.

***elastic material** A material that returns to its original shape after being stressed or strained.

***electromagnetic waves** A wave, partly electric and partly magnetic, that carries energy and is given off by vibrating electric charges.

***electron** Subatomic particle with negative charge and mass much less than the proton.

***Element **A pure chemical substance that cannot be broken down into anything simpler by chemical or physical means; there are over 100 known elements, the fundamental materials of which all matter is made

***elongation strain** The ratio of the increase in length to the unstretched length of the spring or stretching device.

***energy** Generally defined as the ability to do work, energy is one of the most important scientific concepts. Energy is conserved, meaning the sum total of all types of energy in a system never changes. Energy is a scalar quantity.

***English units** Used in the English system (also called the British Engineering System) of measurement, which uses the foot as the basic unit for measuring length, the pound as the basic unit for measuring force, and the second as the basic unit for measuring time.

***evaporation** The phase change from liquid to gas that occurs at the surface of a liquid.

***focal point** The point at which a beam of light parallel to the principal axis converges.

***force** A push or a pull. That which accelerates an object. Force is a vector quantity. F=ma

***frame of reference** In physics, a set of established physical conditions, including the appointment of coordinate axes, which defines a specific system and enables the unambiguous description of movement or placement within the system, and which provides a basis for mathematical statements of physical laws.

***free fall** An object in motion under the influence of gravity only.

***frequency** The number of vibrations per unit of time, measured in hertz (Hz).

***friction** A force which resists the attempted or relative motion of two bodies in contact. The force of friction always acts in a direction opposite to the motion.

***fulcrum** The pivotal point or support point of a lever or simple machine.

***Galilean principle of relativity** The laws of motion are the same for any two inertial reference systems.

***Galileo** An astronomer and physicist from Italy (1564-1642), Galileo was the first astronomer to use a telescope for studying the stars. He was imprisoned in 1633 because he insisted the sun -- not the earth -- was the center of what we now know as our solar system.

***Gamma ray **Very short wavelength electromagnetic radiation emitted by decaying nuclei

***gravity** The force of attraction between two massive bodies; Objects fall due to the acceleration of gravity, which is commonly estimated on the surface of the earth as 9.8 m/s^{2 }in circumstances where air resistance is understood to be negligible.

***gravitational constant **The constant G which appears in the equation for Newton's law of gravitation is called the universal constant of gravitation or the gravitational constant. Numerically it is equal to the force of gravitation, which acts between two bodies of mass 1kg each separated by a distance of 1m. The value of G is 6.6710^-11 Nm^{2}/kg^{}.

***greenhouse effect** The effect realized when the short-wavelength radiant energy emitted from the sun enters the earths atmosphere and is absorbed by the earth more easily than the long-wavelength energy from the earth can leave.

***heat** A form of energy associated with the movement of atoms and molecules. The transfer of heat is from higher to lower temperatures and results in either a gain or loss of internal energy.

***heat of fusion** The energy per gram that leaves a substance when it changes from the liquid state to solid state.

***Hertz **Unit of frequency; equivalent to one cycle per second.

***Hooke, Robert** Scientist who found that the amount of elongation in elastic solids such as a spring is directly proportional to the deforming force.

***Hooke's law** The rule which states that the amount of compression or stretch (x) is directly proportional to the applied force (F): **F~ x**.

***horsepower** A unit of power defined as 550 foot-pounds per second (ft-lb/s); Originally chosen by James Watt, who observed that a good horse can work all day at an average rate of about 360 ft-lb/s. Symbolized as hp. **See also**: foot-pound; watt.

***impulse** The time interval during which a force acts; The product of force and time; The application of impulse results in change in momentum.

***incandescent **Matter emitting visible light as a result of high temperature for example, a light bulb, a flame from any burning source, and the sun are all incandescent sources because of high temperature.

***inclined plane** A simple machine that is made of a plane set at an angle to the horizontal. It is used to raise or lower a load by sliding or rolling.

***inelastic** Materials that do not go back to the same shape they were before they were changed or distorted.

***inelastic collision** Collisions in which heat is generated or the objects are deformed.

***inelastic material** A material that does not return to its original shape after being stressed or strained.

***inertia** The tendency of a body at rest to stay at rest and of a body in motion to stay in motion. Resistance to change.** See also:** Newton's first law of motion.

***inertial** Adjective form of the root word "inertia".

***inertial reference frame** Reference frames or systems in which Newton's first law of motion is valid. All inertial reference frames are equivalent.

***Interference **Phenomenon of light where the relative phase difference between two light waves produces light or dark spots, a result of light's wavelike nature

***isotope** A form of an element having a particular number of neutrons in the nucleus.

***instantaneous speed** The actual speed at any given instant. Example: The reading on the speedometer of a car.

***insulator** A material that is a poor conductor of heat or electricity. Usually a non-metal.

***joule** The SI unit measuring work and other forms of energy. Equal to a force of one newton (N) exerted on a body moved one-meter (m) in the same direction as the force. Symbolized as J.

***Kelvin Scale **On this scale, the ice-point (the lower fixed point) is taken as 273.15K and the (the upper fixed point) is taken as 373.15K. The interval between these two points is divided into 100 equal parts. Each division is equal to 1K.

***kinematics** The science of how objects move.

***kinetic energy** The energy possessed by matter (objects, bodies, particles, etc.) due to motion. Examples: The wrecking ball uses kinetic energy to destroy the building as it strikes the walls; The roller coaster car uses kinetic energy as it rolls down a big hill. In Newtonian (nonrelativistic) physics: The energy of motion, equal to half the mass, multiplied by the square of the speed: **E _{motion} = (m/2)(s/t)^{2}**.

***kilogram **The fundamental unit of mass in the metric system of measurement, which is about equal to 2.2 lbs.

***latent heat of vaporization** The amount of heat needed to change one gram of a liquid at its boiling point from the liquid state to the vapor state.

***law of conservation of angular momentum** The angular momentum of a system or an object remains unchanged unless acted upon by an external net (unbalanced) torque.

***law of conservation of energy** Although energy can change from one form into another the total amount of energy never changes. Energy cannot be created or destroyed. Energy is conserved.

***law of conservation of momentum** The momentum of a system or an object remains unchanged unless acted upon by an external net (unbalanced) force. Also called the law of conservation of linear momentum.

***law of universal gravitation** Two objects attract each other with a force that is proportional to the product of the masses of both objects, and inversely proportional to the square of the distance between the centers of mass of the objects.

***length contraction** In relativistic physics, the effect that lengths and distances are shorter in a moving system as seen by an observer not moving with the system compared to lengths and distances in the system that is not moving, relatively speaking. Length contraction only happens along the direction of motion.

***lens** A piece of transparent material that can bend rays of light.

***lever** A simple machine that is made of a bar or pole that turns about a fixed point.

***lever arm** When an applied force is perpendicular, the distance from the turning axis to the point of application is termed the lever arm.

***lift** A term used in application of Bernoullis principle. It is the net upward force created by the difference between upward and downward pressures. Horizontal flight is feasible when lift equals weight.

***linear velocity** See: velocity.

***liter **A metric system unit of volume, usually used for liquids. A space that is (10 cm)^{3}.

***magnetic field **Model used to describe how magnetic forces on moving charges act at a distance

***magnitude** A number assigned to a quantity so that it can be compared with other quantities. Magnitude specifies size or length, but not direction. It is the only component of a scalar quantity. **See also:** vector quantity; absolute value.

***malleable** The quality of a material (usually metal) that it can easily be hammered into thin sheets. **See also:** ductile.

***mass** The quantity of matter in an object.

***mass-energy equivalence** From Einstein's theory of special relativity, the law that says mass and energy are interchangeable and therefore are conserved. A particle at rest in a specific reference frame has total rest energy (E_{o}) equal to the mass at rest (m_{o}) times the speed of light (c) squared: **E _{o} = m_{o}c^{2}**. In a more generalized form, the relationship that the change in amount of energy (D E) of a given body or system is equal to the change in quantity of mass (D m) of the body or system times the speed of light (c) squared: D

***matter **Anything that occupies space and has mass

***Maxwell, James Clerk** English physicist (1831-1879) known for his contributions to the early studies of electromagnetic phenomena as well as the kinetics of gases.

***mechanical advantage** The ratio of the output force to the input force of a machine. Sometimes abbreviated or symbolized as M.A.

***mechanical energy** The sum total of kinetic and potential energy of a system at any given moment. **See also:** potential energy; kinetic energy.

***meter **The fundemental unit of length in the metric system, which is about 39 inches.

***metric system** A decimal system of measurement which uses the meter as the basic unit for measuring length, the kilogram as the basic unit for measuring mass, and the second as the basic unit for measuring time. **See also:** SI units.

***Michelson, Albert** German-born American physicist (1852-1931) who won a Nobel Prize in 1907 for his investigations regarding the speed of light. He collaborated with Edward Morley in experiments which disproved the existence of an atmospheric "ether" through which electromagnetic waves were thought to travel.

***momentum** The inertia of motion; Momentum (p) is calculated by multiplying the mass (m) and velocity (v): **p = mv**. A vector quantity, it is also called linear momentum.

***net force** Net force refers to the combination of forces acting on an object. See: force

***neutron** Subatomic particle with no charge and mass slightly larger than the proton.

***newton** A metric system unit for force, symbolized as N. Force equals mass times acceleration (F = ma), and the units used for newtons of force are: **kg m/s ^{2}**

***Newton, Isaac** Sir Isaac Newton (1642-1727) was an English mathematician and scientist who invented differential calculus and contributed many important theories of math and physics. His three laws of motion are fundamental to studies of nonrelativistic (pre-Einstein) physics, often referred to as "Newtonian" physics.

***Newtons first law of motion** A body continues in its state of motion in a straight line at constant speed, or in its state of rest, unless a net force acts upon it. **See also:** inertia.

***Newtons laws** In physics, a set of rules, developed by Sir Isaac Newton, to describe the motion of ordinary objects. **See also: **Newton's first law; Newton's second law; Newton's third law.

***Newtons second law of motion** When a net force acts upon a body, the acceleration it produces is directly proportional to its magnitude, the direction of the acceleration is in the same direction as the applied force, and the magnitude of the acceleration is inversely proportional to the mass of the body. Also described as: Force (f) equals mass (m) multiplied by acceleration (a): **f = ma**.

*Newtons third law of motion Whenever an object exerts a force on another object, the second object exerts an equal (in magnitude) and opposite (in direction) force on the first.

***Newtonian physics** Physics of phenomena that are not moving at speeds near the speed of light. Physics of mechanical phenomena that are described using Newton's laws of motion.

***newton-meter** A metric system unit used to measure work (force times distance); It is symbolized as N-m.

***noise **Sounds made up of groups of waves of random frequency and intensity

***non-relative motion** The act or process of changing position or place without taking into consideration other positions or places.

***normal **A line perpendicular to the surface of a boundary

***normal force** Force acting at a 90 angle to a surface or point of contact is referred to as the normal force.

***ohm **Unit of resistance; equivalent to volts/amps

***opaque** Material that does not allow light to pass through.

***oscillatory motion **The back and forth motion of a body about its mean position is called oscillatory motion. Oscillatory motion is also called vibratory motion. Oscillatory motion is periodic in nature.

***pascal** SI unit of pressure; one newton per square meter.

***photon** A particle of light with wave-like properties.

***plasma** State of matter in which atoms are seperated into electrons and positive nuclei.

***polarized light **Light whose constituent transverse waves are all vibrating in the same plane; also known as planepolarized light

***potential energy** Stored energy; The energy of matter (objects, bodies, particles, etc.) derived from position or configuration rather than motion. Examples: The potential energy contained in a tightly wound spring is due to its configuration. The potential energy contained in the roller coaster car poised high above the ground is due to its position. **See also:** kinetic energy; mechanical energy.

***power** The rate at which energy is transformed or work is done; Commonly measured in units of watt (W), horsepower (hp), joules-per-second (J/s), foot-pounds (ft-lb), or British thermal units-per-time (Btu/hr).

***precision** The degree of exactness in a measurement.

***pressure** The force per unit area. For liquids and gasses, force per unit area exerted by a fluid on its container.

***projectile motion** First described by Galileo, projectile motion is governed by the principle that an object dropped vertically and an object projected horizontally from the same height will reach the ground at the same time. This idealized description assumes air resistance is negligible and the only force acting upon either object (once they have been dropped or projected) is gravity. Examples of projectile motion include the flight of a golf ball and the trajectory of a speeding bullet.

***pulley** A simple machine that works as a lever, it consists of a wheel with a grooved rim in which a pulled rope or chain can run; Used to change the direction of a pull (a force) or to multiply force.

***proton** Subatomic particle with positive charge. The nucleus of the hydrogen atom.

***Pythagoras** A Greek philosopher (ca. 600 BC) who is regarded as the first mathematician; He proved the relationship, known now as the Pythagorean Theorem, which correlates the lengths of the sides of a right triangle.

***Pythagorean theorem** The mathematical proposition that the square of the hypotenuse of a right triangle is equal to the sum of the squares of the other two sides.

***quanta **Fixed amounts; usually referring to fixed amounts of energy absorbed or emitted by matter

***quantum mechanics **Model of the atom based on the wave nature of subatomic particles, the mechanics of electron waves; also called wave mechanics

***radian **SI unit of angular measure, which is equal to 57.3 degrees.

***radiation** The energy sent by electromagnetic waves. The particles emitted by radioactive atoms, such as uranium.

***rarefraction ** A part of a longitudinal wave in which the density of the particles of the medium is less than the normal density is called a rarefaction.

***reaction force** The second force referred to in Newtons third law of motion. **See also**: action force.

***real image **An image generated by a lens or mirror that can be projected onto a screen

***reflection **The change when light, sound, or other waves bounce backwards off a boundary

***regelation** The phenomenon that occurs when ice melts under pressure and then freezes again when the pressure is reduced.

***relative** In physics, depending upon a point of view or frame of reference; Taken "in relation to" something else; Similar in meaning to the phrase "with respect to".

***relative motion** The act or process of changing position or place in comparison with some other position or place.

***relativistic kinetic energy** The kinetic energy of an object moving near the speed of light

***relativistic mass** The effect that the mass of a body in motion increases as the speed of the body increases.

***relativistic physics** Physics of or relating to or resulting from phenomena traveling near the speed of light.

***resonance **When the frequency of an external force matches the natural frequency and standing waves are set up

***rest energy** The energy possessed by an object that is not in motion. Sometimes called the energy of being. Symbolized as E_{o}.

***rest mass** The fixed mass of an object, independent of speed or energy. Rest mass does not change.

***resultant** In physics, the sum of two or more vectors or of two or more vector quantities, such as resultant force or resultant acceleration.

***rotational inertia** The tendency of an object to stay in its state of rotation.

***rotational motion** When all points in a body move in circles and the centers of the circles all lie on a line (called the axis of rotation) that is perpendicular to the circles. The centers of the circles do not move.

***rotational speed** See: angular speed.

***rotational velocity** See: angular velocity.

***scalar quantity** A number which is completely specified by its size or magnitude, and which has no associated direction. Examples include energy, mass, volume, speed, and time.

***scaling** The study of how size affects the relationships between weight, strength, and surface area.

***shear strain** Strain due to particles moving in a direction parallel to the area over which the force acts.

***SI units** Originally established in France ca. 1790s, *Le Systeme International* is referred to in English as the "international system" of metric measure. Shortened versions of SI units' names are called symbols (not abbreviations). **See also:** metric system.

***simple machine** A mechanical device used to transfer energy from one place to another, to change the direction of a force, or to increase a force or a speed. Examples: lever, wheel and axle, and inclined plane.

***solids** Matter composed of particles that are held in relatively fixed positions.

***specific heat** The quantity of heat necessary to raise the temperature of a unit mass of a substance one degree Celsius.

***speed** The rate at which something travels a certain distance. It is always measured in terms of a distance divided by time. In physics, the most common units for speed are meters-per-second (m/s). Speed is a scalar quantity.

***spring constant, k** The proportionality constant in the Hooke's Law equation.

***standing wave **Condition where two waves of equal frequency traveling in opposite directions meet and form stationary regions of maximum displacement due to constructive interference and stationary regions of zero displacement due to destructive interference

***strain** The relative amount of deformation produced in a body under stress.

***stress** The ratio of the internal force, F, to the area, A, over which the force acts.

***surface tension** A term for the tension created when a force acts on a liquid surface film and exerts an equal and opposite force that restores the horizontal surface.

***tensile strength** The maximum tension a material can bear before it begins to tear.

***terminal speed** The ultimate speed of a falling object, when acceleration reaches zero because the rate of speed is no longer changing with respect to time. This occurs when the forces of air resistance balance the weight of the falling object.

***terminal velocity** Terminal velocity is the vector quantity that indicates the direction of motion of an object traveling at terminal speed.

***time dilation** In relativistic physics, the effect that clocks run slower in a moving system compared to clocks in a system that is at rest, relatively speaking, as seen by an observer in the latter system.

***time period **The time taken to complete one oscillation is called the time period of an oscillation. The time period of a pendulum does not depend upon the mass of the bob and amplitude of oscillation. The time period of a pendulum is directly proportional to the square root of the length and inversely proportional to the square root of the acceleration due to gravity.

***torque** Force applied with leverage that produces rotational movement; force applied to a rotating body in a way that changes the rotation. Symbolized by t. The angular analog to force, torque is calculated as the product of the perpendicular component of the applied force (F^ ) and the length of the lever arm (*l*) used to apply it: **F^ l**.

***total internal reflection **Condition where all light is reflected back from a boundary between materials; occurs when light arrives at a boundary at the critical angle or beyond

***translucent** materials that allow light to pass through in bent lines.

***transparent** materials that allow light to pass through in straight lines.

***trough **The point of maximum negative displacement on a transverse wave is called a trough.

***universal law of gravitation **Every object in the universe is attracted to every other object with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between the centers of the two masses

***vector quantity** In physics, something that is specified in terms of both magnitude and direction. Examples include force, torque, and acceleration.

***vectors** In physics, quantities that have directions assigned to them.

***velocity** Speed in a given direction. When a car is said to be going 55 mph, the speed is being described. To specify its velocity, the speed must also be accompanied by a description of the direction in which the car is moving. Examples: 55 mph to the south; 70 mph going east. Also called linear velocity. **See also: **angular velocity; average velocity.

***virtual image ** Point from which light rays appear to diverge without actually doing so.

***volt** The SI unit of electrical potential (symbol V).

***volume** The amount of space occupied by a three-dimensional object or space, expressed in cubic units and symbolized as V.

***watt** An SI (metric system) unit used to measure power, 746 watts are equal to one horsepower. Symbolized as W.

***wavelength **The distance between the two nearest points on a wave, which are in the same phase, is called the wavelength of the wave. The distance between two adjacent crests or two adjacent troughs is called its wavelength.

***wedge** A simple machine consisting of a piece of material such as metal or wood that is thick at one end and tapers to a thin edge at the other end. It is inserted in narrow crevices where it is used for splitting, tightening, securing, levering, etc.

***weight** Force on a body due to the gravitational attraction of another body, usually the earth. The force of gravity on an object.

***work** In linear physics, the force on an object multiplied by the distance the object is moved by the force in a direction parallel to the force. In rotational physics, the torque multiplied by the angular rotation.

***X ray** High-energy photons; High-frequency, short-wavelength elecromagnetic waves.

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