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radioactivity | Physics | 1 | The spontaneous emission of radiation from an atom’s nucleus. |
radioisotope | Physics | 1 | An atom with an unstable nucleus. The excess energy associated with the nucleus is released when the nucleus undergoes radioactive decay. |
rayleigh scattering of light | Physics | 1 | The reflection of light by very small particles that are smaller than the wavelength of light. This type of scattering causes the blue colour of the daytime sky, the reddening of the Sun at sunset and the yellow colour of the Sun. |
reflection | Physics | 1 | 1. The change in direction, or bouncing back of a wave when it strikes a surface. 2. Mirroring. 3. Casting back, as in light or heat. |
resistance | Physics | 1 | 1. The opposition to the flow of electric current through a circuit. 2. The ability to withstand harmful or unfavourable conditions, such as an infectious disease. |
resonance | Physics | 1 | An amplified wave amplitude produced when the frequency of the source matches the natural frequency of the object vibrating. |
resultant force | Physics | 1 | The overall force that acts on an object. For straight-line motion, the resultant force is the sum of the individual forces acting in one direction minus the forces acting in the opposite direction. |
rolling resistance | Physics | 1 | The force that opposes motion as a tyre (or other rolling object) rolls over the ground. Rolling resistance is caused as energy is converted into heat energy. |
rpm | Physics | 1 | A measure of centrifuge speed. |
revolutions per minute | Physics | 1 | A measure of centrifuge speed. |
s-waves | Physics | 1 | Seismic waves that travel though side to side movements. They can travel through solid only. They are also called shear waves. |
seismic velocity | Physics | 1 | The speed at which seismic waves travel. |
sferic | Physics | 1 | A radio emission generated as part of the electromagnetic radiation produced in a lightning discharge. |
skin friction | Physics | 1 | The opposing force caused as particles of air (or another fluid) move over the surface of an object. Collisions cause the air particles to change speed. |
snell’s law | Physics | 1 | Snell’s Law of Refraction is expressed as n1sinθ1= n2sinθ2. The law states that, for waves passing from one medium to another, the ratio of the sine of the angle of incidence and the sine of the angle of refraction is constant. |
solid state physics | Physics | 1 | The study of rigid matter or solids. |
spectrometer | Physics | 1 | An instrument that collects information about the different parts of the electromagnetic spectrum coming from a light source. |
specular reflection | Physics | 1 | The reflection of light from a smooth surface in which the incident light rays are reflected from the surface such that the angle of reflection equals the angle of incidence. |
states of matter | Physics | 1 | The classical states of matter are solid, liquid and gas. Several other states, such as plasma, do exist. Plasma is the most common form of matter in the universe. |
static electricity | Physics | 1 | An electrical charge that has accumulated on an object. |
stepped leader | Physics | 1 | A faint luminous light that branches down from a thunderstorm cloud basetowards the ground before a lightning flash. It is seen to rapidly grow towards the ground in 50 m steps, and as it nears the ground, a positively charged streamer fires upwards to connect with it. |
stp | Physics | 1 | Standard temperature and pressure is taken as a temperature of 0°C (273 K) and a pressure of 101.3 kPa. |
streamer | Physics | 1 | An upwardly propagating positively charged channel that meets a stepped leader to form a lightning bolt. |
subatomic particles | Physics | 1 | Particles that make up atoms – the building blocks of matter. The three basic ones are protons, neutrons and electrons. Protons and neutrons are themselves made of even smaller particles called quarks. |
subduction | Physics | 1 | When tectonic plates with differing material densities collide and the denser plate is forced down under (subducts) the less dense one. |
superconducting magnet | Physics | 1 | The phenomenon of almost perfect conductivity shown by certain substances at temperatures approaching absolute zero. |
superconductivity | Physics | 1 | The ability of certain substances to conduct electric current with almost no resistance at very low temperatures. |
surface tension | Physics | 1 | A property of liquids caused by intermolecular forces near the surface causing an elastic-like force or the apparent presence of a surface film. |
synchrotron | Physics | 1 | A type of particle accelerator in which particles move at accelerating speed around a hollow ring – sometimes several kilometres in circumference. The ion beam or particle path is very precisely focused by the magnetic field of a continuous ring of electromagnets. |
tension | Physics | 1 | A force tending to stretch or elongate something. |
terminal velocity | Physics | 1 | The constant speed that an object travels at once the forces acting on it become balanced. |
theory | Physics | 1 | To scientists, a theory provides a coherent explanation that holds true for a large number of facts and observations about the natural world. It has to be internally consistent, based upon evidence, tested against a wide range of phenomena and demonstrate problem solving. |
thermal energy | Physics | 1 | All forms of matter have internal or thermal energy. This comes about as a result of particle motion (kinetic energy) as well as the energy stored in chemical bonds present in the particles themselves (potential energy). |
thermal expansion | Physics | 1 | The tendency of matter to change in shape, area and volume in response to a change in temperature. |
thermal reactor | Physics | 1 | A nuclear reactor in which nuclear fissions are caused by neutrons that are slowed down by a moderator. |
thermal shock resistance | Physics | 1 | The ability of a material to withstand rapid heating followed by rapid cooling over many cycles. |
thermophilic | Physics | 1 | Requiring very high temperatures for normal growth and development (thermo=heat; philic=fond). |
thixotropic | Physics | 1 | A substance that is gel-like when still, but liquid when agitated. |
tokamak | Physics | 1 | A device for producing controlled nuclear fusion. Its design allows for the generation, heating and confinement of extremely hot plasma. |
transform boundaries | Physics | 1 | An area where two tectonic plates meet and slide horizontally past each other. Crust is neither produced nor destroyed. |
transmission of light | Physics | 1 | If light falling on an object is allowed to pass through, it is called transmitted light. Objects that allow this to happen are called transparent. |
transuranium element | Physics | 1 | An element with an atomic number greater than 92. |
triboelectricity | Physics | 1 | The electric charge transfer between two objects when they come in contact or are rubbed against each other. Static electricity is an example of the triboelectric effect. Thetriboelectric seriesis a list of materials ranked by their tendency to lose or gain electrons, in comparison to other materials on the list. |
triple point of water | Physics | 1 | The temperature and pressure at which the three phases of water (liquid water, solid ice and gaseous water vapour) exist in equilibrium (a temperature of 0.01°C or 273.16 K and a pressure of 611.73 Pa). |
turbulent flow | Physics | 1 | The swirling motion of air (or other fluids) caused as an object moves through it. Turbulent flow is created when the airflow separates from the surface of an object. |
unbalanced force | Physics | 1 | When the forces pushing an object in one direction are greater than the forces pushing in the opposite direction. Also known as the resultant or net force. |
vaporisation | Physics | 1 | A change of state that converts a substance from its liquid form to its gaseous form. |
visible light spectrum | Physics | 1 | Electromagnetic waves in the range visible to the human eye. These waves have a wavelength from about 400 nanometres in the violet to about 770 nanometres in the red. Light behaves both as a particle and a wave. A particle of light is known as a photon. |
weight | Physics | 1 | Force due to gravity acting on an object, measured in newtons. |
axis | Physics | 1 | An imaginary straight line around which an object spins. |
circuit | Physics | 1 | The complete path of an electric current. |
drag | Physics | 1 | Resistance to motion through the air. |
escape velocity | Physics | 1 | The speed needed for an object to break away from the gravitational pull ofa planet or moon. |
fluid | Physics | 1 | A substance that flows; any liquid or gas. |
hypersonic | Physics | 1 | Able to reach speeds equal to or more than five times the speed of sound. |
magnet | Physics | 1 | A material or object that produces aforcethat pulls on other magneticmaterials. |
matter | Physics | 1 | Anything that has weight and takes up space, as a solid, liquid or gas. |
microgravity | Physics | 1 | The condition of being weightless, or of the near absence of gravity. |
propulsion | Physics | 1 | Theforcethat pushes forward or drives an object forward. |
rotate | Physics | 1 | To turn around in a circle; to spin. |
sonic boom | Physics | 1 | A loud noise caused by the meeting of shock waves made when an objectgoes faster than thespeed of sound. |
thrust | Physics | 1 | A forward or upward push. |
vortex | Physics | 1 | A whirling or spinning mass, as of water or air; whirlpool or whirlwind. |
weight | Physics | 1 | The measure of the pull ofgravityon an object. |
ω | Physics | 1 | How fast an object rotates or revolves relative to another point, i.e. how fast the angular position or orientation of an object changes with time. There are two types of angular velocity: orbital angular velocity and spin angular velocity. Spin angular velocity refers to how fast a rigid body rotates with respect to its centre of rotation. Orbital angular velocity refers to how fast a rigid body's centre of rotation revolves about a fixed origin, i.e. the time rate of change of its angular position relative to the origin. In general, angular velocity is measured in angle per unit time, e.g. radians per second. The SI unit of angular velocity is expressed as radians/sec with the radian having a dimensionless value of unity, thus the SI units of angular velocity are listed as 1/sec. Angular velocity is usually represented by the Greek letter omega (ω, sometimes Ω). By convention, positive angular velocity indicates counter-clockwise rotation, while negative is clockwise. |
△θcase | Physics | 1 | The difference between the temperature of the hottest point of the container and the temperature of the cooling air. |
absolute zero | Chemistry | 1 | A theoretical condition concerning a system at the lowest limit of the thermodynamic temperature scale, or zero kelvins, at which the system does not emit or absorb energy (i.e. all atoms are at rest). By extrapolating the ideal gas law, the internationally agreed-upon value for absolute zero has been determined as −273.15 °C (−459.67 °F; 0.00 K). |
absorption | Chemistry | 1 | 1. The physical or chemical process by which a substance in one state becomes incorporated into and retained by another substance of a different state. Absorption differs from adsorption in that the first substance permeates the entire bulk of the second substance, rather than just adhering to the surface. |
accuracy | Chemistry | 1 | How close a measured value is to the actual or true value. Compare precision. |
achiral | Chemistry | 1 | (of a molecule) Having the geometric symmetry of being indistinguishable from its own mirror image; lacking chirality. |
acid | Chemistry | 1 | A hydrogen-containing substance that is capable of donating a hydrogen ion to another substance. |
acid anhydride | Chemistry | 1 | Any chemical compound derived by the removal of water molecules from an acid. Contrast base anhydride. |
acid dissociation constant | Chemistry | 1 | A quantitative measure of the strength of an acid in solution expressed as an equilibrium constant for a chemical dissociation reaction in the context of acid-base reactions. It is often given as its base-10 cologarithm, pKa. |
ka | Chemistry | 1 | A quantitative measure of the strength of an acid in solution expressed as an equilibrium constant for a chemical dissociation reaction in the context of acid-base reactions. It is often given as its base-10 cologarithm, pKa. |
acid–base extraction | Chemistry | 1 | A chemical reaction in which chemical species are separated from other acids and bases. |
actinides | Chemistry | 1 | The periodic series of metallic elements with atomic numbers 89 to 103, from actinium through lawrencium. |
activated complex | Chemistry | 1 | A structure that forms because of a collision between molecules while new bonds are formed. |
activation energy | Chemistry | 1 | The minimum energy which must be available to a chemical system with potential reactants in order to result in a particular chemical reaction. |
activity series | Chemistry | 1 | See reactivity series. |
acyclic | Chemistry | 1 | Containing only linear structures of atoms (particularly in hydrocarbons). |
addition reaction | Chemistry | 1 | In organic chemistry, a type of chemical reaction in which two or more molecules combine to make a larger one. |
adduct | Chemistry | 1 | A distinct chemical species that is the sole product of an addition reaction between two other distinct reactant species, in which all of the atoms comprising the reactants are retained in the single product. Changes in connectivity may occur, but there is no loss of any of the original atoms and no gain of atoms that are not present in the reactant molecules. Stoichiometries other than 1:1 are also possible, e.g. a bis-adduct (2:1). |
adhesion | Chemistry | 1 | The tendency of dissimilar particles or surfaces to cling to one another as a result of intermolecular forces. Contrast cohesion. |
adsorption | Chemistry | 1 | The chemical adhesion of atoms, ions, or molecules of one substance (either a gas, liquid, or dissolved solid) to the surface of another substance, resulting in a film of the first substance being weakly bonded to the interface between the two substances. Adsorption differs from absorption in that it is exclusively a surface phenomenon, while absorption involves entire volumes of materials. |
aeration | Chemistry | 1 | The mixing of air into a liquid or a solid. |
alcohol | Chemistry | 1 | Any organic compound consisting of at least one hydroxyl group attached to a saturated carbon atom. Alcohols have the general formula R–OH. |
aldehyde | Chemistry | 1 | A functional group and a class of organic compounds consisting of a carbonyl group attached to a hydrogen atom and any other R-group. Aldehydes have the general formula R–C(H)=O. |
alkali metal | Chemistry | 1 | Any of the metallic elements belonging to Group 1 of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). |
alkaline earth metal | Chemistry | 1 | Any of the metallic elements belonging to Group 2 of the periodic table: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). |
alkane | Chemistry | 1 | Any fully saturated acyclic hydrocarbon, i.e. one in which all carbon–carbon bonds are single bonds. |
alkene | Chemistry | 1 | Any unsaturated hydrocarbon containing at least one carbon–carbon double bond. |
alkyl | Chemistry | 1 | The substituent form of an alkane, i.e. any alkane missing a hydrogen atom. The term may be used to broadly describe many different functional groups, e.g. a methyl, ethyl, or propyl group. |
alkyne | Chemistry | 1 | Any unsaturated hydrocarbon containing at least one carbon–carbon triple bond. |
allomer | Chemistry | 1 | A substance that differs in chemical composition but has the same crystalline structure as another substance. |
allotrope | Chemistry | 1 | Any of a variety of different structural forms of the same element, as with carbon, whose allotropes include diamonds, graphite, and fullerene. |
alloy | Chemistry | 1 | A mixture of metals or of a metal and another element which in combination exhibit a metallic bonding character. Common examples include bronze, brass, and pewter. |
amalgam | Chemistry | 1 | A mixture of metals based on mercury. |
ambident | Chemistry | 1 | A molecule or functional group that has two alternative and interacting reaction sites, to either of which a bond may be made during a reaction. |
ammoniacal | Chemistry | 1 | Describing a solution in which the solvent is aqueous ammonia. |
amount of substance | Chemistry | 1 | The number of discrete particles (such as molecules, atoms, ions, electrons, or any other atomic-scale entity) in a given sample of matter, divided by the Avogadro constant. The SI unit for amount of substance is the mole (mol). |
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