Science Glossary A - K

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Air resistance
Air resistance is a frictional force experienced by objects as they move through air or as air flows around them. It generally opposes the motion of the object or the air flow around it, and is created by the air rubbing on the outside surface of the object. Students often neglect its influence because it is difficult to calculate and only of significance with high relative speeds or large surface areas. It is responsible for the operation of parachutes and important in the design of aircraft and cyclone tolerant buildings.

Arteries are muscular blood vessels in the body that transport blood away from the heart to capillaries or the lungs. Most arteries convey blood rich in oxygen or, in the case of the pulmonary arteries that carry blood from the heart to the lungs, carbon dioxide. Arteries have elastic walls that allow the pressure from the heart’s pumping to be transmitted along the artery.

Artificial light source
A luminous object which is manufactured or controlled by humans. E.g. incandescent and fluorescent light bulbs, light emitting diodes (LED’s), torches and electroluminescent devices.

is taking on the traits of another culture, leaving the culture of origin behind while embracing the new one.

Atmospheric pressure
Atmospheric pressure is the weight force exerted on an area by the weight of a vertical column of air rising above the surface area to the upper reaches of the Earth’s atmosphere. Sometimes referred to as ‘barometric pressure’ or simply as ‘air pressure’ it varies due to changes in local weather conditions. At sea level it is approximately equal to a weight of 1kg per square cm or 10 tonnes per square metre. We only notice the effects of this potentially very large force when the air is acting on only one side of a surface.

Atoms are a fundamental building block of matter; a small number (less than 90) of different types of atoms make up the very large number of substances we encounter. Atoms are neither created nor destroyed in (non-nuclear) physical and chemical changes – they merely rearranged, with the total number not changing. The substances we call elements are those that contain only one kind of atom. Students find it very difficult to imagine how small atoms are. Atoms are composed of more fundamental particles, the most important being electrons, protons and neutrons. The positively charged protons and the neutrally charged neutrons reside in a relatively small nucleus at the centre of the atom where nearly all the mass of an atom is concentrated.

Atomic mass
The atomic mass is the sum of the individual masses of all the protons and neutrons found in the nucleus of an atom. Because the mass of an individual atom is so small it is more convenient to express it as a relative mass using the mass of a carbon 12 atom as equivalent to 12 units of atomic mass.

Attractive force
‘Attractive force’ is a term applied to non contact forces which result in objects being ‘drawn together’. These forces may be electrostatic, magnetic or gravitational. The attractive forces between atoms and molecules that hold liquid and solid particles together are electrostatic.


Big Bang
a cosmological theory in which the expansion of the universe is presumed to have begun with a primeval explosion referred to as the ‘Big Bang’. This giant explosion around 14 billion years ago expanded rapidly, cooled and coalesced into the universe we observe today.

A biochemical refers to particular products of chemical reactions associated with biological functions in living organisms. It is also used as an adjective for the (typically complex) chemical reactions that occur in living things.

Blood Vessels
The blood vessels are flexible tubular canals through which blood circulates throughout the body. The blood vessels are part of the circulatory system. Arteries, veins, and capillaries are all kinds of blood vessels. Arteries carry blood from the heart to capillaries which are the smallest type of blood vessels. Capillaries have very thin walls which allow liquids and gases to exchange between cells and the blood. Veins then return blood containing wastes to organs for its removal and then on to the heart for circulation.

Brownian motion
Brownian motion is the random movement of molecules in a liquid or gas due to their thermal energy. This term is named after the botanist Robert Brown who observed the random motion of tiny pollen grains as they were nudged by their collision with water molecules.


a unit of energy widely used to measure the chemical energy in food. It is equal to the amount of heat energy required to raise the temperature of 1 gram of water 1°C and is equivalent to 4.184 joule. Some confusion exists when this term is used in the context of food where the kilocalorie is also used, but is often written as Calorie or Cal. One Calorie (or ‘large’ calorie - capital C) is equal to one kilocalorie (or 1000 calories – small c).

Capillaries are the smallest of a body's blood vessels which connect arteries and veins. They are important for the exchange of gases, such as oxygen and carbon dioxide, and other substances between the blood and cells. The walls of capillaries are very thin and are often composed of only a single layer of cells. This allows molecules such as oxygen and water and waste products such as carbon dioxide and urea to pass through them. This property of capillary walls is critical to the role that the circulatory system has in collecting and transporting different substances to and from different parts of our bodies.

A characteristic is a distinguishing feature or quality of an organism that helps to define, identify or describe it.

Chemical bond
A chemical bond is a non contact force holding atoms together in a combined state. This force may result from the attraction of opposite charges (ionic bond), the magnetic and electrical attraction of shared electrons (covalent bond), or a combination of these attractions.

Chromosomes are thread-like bodies, usually x shaped and usually found in pairs in the nuclei of living cells. They carry genetic information that determines the inherited characteristics of an organism. Chromosomes consist of deoxyribonucleic acid (DNA) and proteins and each chromosome can be regarded as comprising a number of genes. Each species can be characterised by the number of chromosomes that its cells contain, for example, humans usually have 46 chromosomes per cell (23 pairs).

Circulatory system
The circulatory system contains the blood vessels (arteries, veins and capillaries) and heart which moves blood throughout the body. Among other things this system provides oxygen and nutrients to cells and aids them in the removal of waste products, fighting infection and general repair.

Closed system
A closed system is a continuous predetermined or prescribed pathway. It may be useful to think of the analogy of trains on a railway line where the trains move around the same track and goods can be transported around the pathway. In the human body the circulatory system is an example of a closed system. The blood travels along a defined, closed pathway of tubular blood vessels comprising a complex system of arteries, capillaries and veins. The blood is contained within this connected system and circulates continuously, never leaving this pathway. Some invertebrate animals such as molluscs, arthropods (such as insects and spiders) have an 'open' circulatory system where organs are bathed in a surrounding fluid which is not contained by tubular vessels. In such an open circulatory system there is no predetermined pathway and there is no distinction between blood and other tissue fluid.

A colloid is formed by the suspension of droplets of liquid or solid particles which are small enough to be kept in constant motion by the molecular movement of the suspending medium. The particles may be suspended in either a liquid or a gas and will not settle out of suspension under the action of gravity alone. Examples are smoke, milk, mayonnaise, whipped cream and aerosols.

Combustion describes the process of burning (rapid oxidation) in which oxygen is chemically combined with a fuel to release energy in the form of light and heat. Combustion occurs in the gaseous state for example, when a candle or wooden log is burning, for example, the reaction (and hence the flame) is always just above the fuel. The variation in ignition temperatures of different fuels reflect the different temperatures needed to get either the fuel or (in cases such as wood) decomposition products of the fuel into the gas state.

any material that does allow electricity to flow through it easily because the electrons in their atoms are able to easily from atom to atom. Most metals are very good conductors. A poor electrical conductor is said to be a good electrical insulator.

A compound is formed by the combination of two or more atoms from different elements in a fixed proportion. The elements in a compound combine to lose their individual properties and to form a substance with new physical and chemical properties.

Compression force
The application of a compression force to an object causes it to become squashed or compacted. Some solid materials like stone and ceramics are able to withstand very large compressive forces with very little measurable deformation which make them a suitable building material for the construction of high walls and columns.

A concentrate is a mixture that has had the majority of its base component, or solvent, removed. Typically this will be the removal of water from a solution or suspension such as the removal of water from fruit juice. The term is also used to describe the removal of much of the unwanted solid matter from a mined ore. The benefit of producing a concentrate is that this reduces the weight of the ore for transportation.

The term consumer is used in biology to refer to an organism that cannot produce its own sources of energy, but feeds on other living organisms. Animals and parasitic plants would be considered consumers. In a food chain, herbivores (animals that eat green plants) are primary consumers and carnivores (that eat herbivores or other carnivores) are secondary consumers.

Continuous view of matter
A continuous view of matter advocates that matter remains divisible into smaller and smaller quantities which continue to maintain the physical and chemical properties of the original sample. This view stands in contrast to the particulate model of matter that advocates that matter is constructed from tiny particles called atoms which are not divisible without the loss of their chemical properties. A continuous view of matter also commonly does not recognise any empty space in matter.

Is the standard unit of electric charge and can be either positive or negative. It is equal to the amount of charge contained on 6.25 X 1018 electrons or the amount of charge that flows past a point in a conducting wire when a current of 1 amp flows for one second.


Diffusion is the movement of molecules in a gas or liquid by random thermal agitation from a region of high concentration to a region of lower concentration.

Digestive system
The digestive system is a series of connected organs from mouth to anus whose purpose is to break down, digest and excrete wastes from the food we eat. The digestive system breaks down complex food molecules into simple molecules, so that they can easily be absorbed into the bloodstream. These molecules are transported in the blood to the body's cells, where they are used for maintenance, growth and reproduction.

DNA is an abbreviation for deoxyribonucleic acid, a complex molecular chain found in the nucleus or cytoplasm of all living cells. DNA acts as a sequence of genetic instructions that encodes proteins and enables cells to reproduce and perform their functions.


An ecosystem is a biological community and its environment. All the dynamic interactions between plants, animals, and the physical environment in which they live make up an ecosystem. No community can carry more organisms than its food, water, and physical environment can accommodate therefore for an ecosystem to be self sustaining these interactions must remain in balance. In an ecosystem, each organism has its own niche, or role, to play. Food and territory are often balanced by natural phenomena such as fire, disease, and the number of predators. Ecosystems may change in function, structure and composition over time due to natural or human disturbance such as drought, flooding, mowing and herbicides.

Elastic collision
An elastic collision describes a collision in which particles rebound without loss of kinetic energy or conversion of this energy into heat, sound or deformation of the particles. For macroscopic objects, no collision is perfectly elastic, however the collisions which occur between molecules in gases, liquids and solids are. If the collisions were not perfectly elastic the motion of the gas molecules would eventually reduce allowing them to be attracted by the weak attractive forces of other molecules and resulting in a change of state to a liquid.

Electrical energy
The term electrical energy refers to energy that is attributed to the movement or position of electrical charges within an electric field. This could include energy derived from both current carrying and static electricity.

Electrical insulator
Any material that does not allow electricity to flow through it easily because the electrons in their atoms do not move easily from atom to atom (i.e. the material has high resistance). Glass, rubber, ceramics and some plastics are good insulators. A poor electrical insulator is said to be a good electrical conductor.

Electromagnetic spectrum
- the complete range of energies of electromagnetic waves from the lowest (largest wavelengths) to the highest (smallest wavelengths) including, in order, electric power transmission, radio waves, infrared, visible light, ultraviolet, X-ray, and gamma ray radiation.

Electrostatic forces
Electrostatic forces are engaging for students because they are examples of a non-contact force that can be easily explored. For example, rubbing balloons or plastic rods create pushes and pulls that can be experienced by objects without making contact. An electrostatic force can either attract or repel other charged objects. All materials are influenced by electrostatic fields although special sensitive equipment is needed to detect its effects. Electrostatic forces are strongly connected to magnetic forces; the fundamental force of ‘electromagnetism’ comprises both these forces.

An element is a pure substance composed of atoms of only one type in that they all have the same number of protons in their nucleus. Each element can be found positioned on the Periodic Table. As the largest number of protons found in the nucleus of any stable atom found on Earth is 92 and not all of these 92 different atoms are stable, there are less than 90 elements that occur naturally on the Earth and 15 or so that have been produced briefly or in small quantities in laboratories. These elements combine into the extremely large number of compounds that we encounter in the world around us.

Endocrine system
The endocrine system uses secretions (hormones) to regulate mood, growth and development and tissue function and to maintain overall metabolism. The endocrine system consists of endocrine glands: the pituitary, thyroid, and adrenal glands. These glands release hormones directly into the circulatory system where they act as chemical messengers coordinating cell behaviour and regulating body functions. All multicellular organisms produce hormones for this purpose.


Ferromagnetism is the common form of magnetism exhibited by metals containing either iron, nickel or cobalt or alloys containing two or more of these metals. These metals become magnetised when they experience a strong magnetic field nearby and are still able to retain this property when the nearby field is removed.

The term field is used to describe a region around a central object in which a second object experiences a force from the central object without being touched by it. Examples are gravitational, magnetic and electric fields. The strength of both electric and magnetic fields reduces very quickly as one moves away from the central object. Although gravity is a relatively weak force in comparison with the other forces, the effects of a gravitational field can extend over astronomical distances. The concept of a field is difficult for students because fields are invisible and their presence can only be inferred by noting how the field influences other objects.

Food web
A food web is a simplified diagrammatic representation of feeding relationships between organisms within an ecosystem. Food webs can be described for a particular environment and generally consist of a series of interconnecting food chains usually beginning with organisms capable of producing ‘food’ (such as green plants) from an energy source (usually the Sun) and connected to organisms that eat them, then organisms that eat those and so on. It is important for students to understand that food webs are diagrams representing only some of the many possible relationships that exist in any given ecosystem.

For students a force is best thought of as a push or pull between objects which may cause one or both objects to change speed and/or the direction of their motion (i.e. accelerate). Most pushes and pulls involve establishing contact between objects using electrostatic forces. All forces are measured in newtons (N) and have a direction associated with them. Physicists identify four fundamental forces: gravitational, electromagnetic (involving both electrostatic and magnetic forces), weak nuclear forces and strong nuclear forces. All interactions between matter can be explained as the action of one or a combination of the four fundamental forces.

Students are very familiar with the effects of friction in retarding an object's motion but less able to identify situations where it is of benefit or essential in aiding motion. Although not completely understood by scientists, it originates from the interaction of electrostatic forces between the surface particles. Friction is a force which opposes the relative motion of two surfaces in contact, and resists or retards their sliding over each other. It can be reduced by applying lubricants and increased with the application of resin or waxes to the surfaces.


A galaxy is a term that describes a complex system of stars held in orbit by mutual gravitational attraction. They may contain upward of 100 billion stars and associated dark matter (i.e. non luminous gas and dust). The Milky Way is the name given to our local galaxy containing the sun. The Milky Way is one of billions of similar galaxies in the observable universe.

A gel is a semi-solid, jellylike material formed from a colloidal solution. By weight, gels are mostly liquid, yet they behave like a cross between a solid and a liquid. Examples are gelatine, hair gel and toothpaste.

Genes are the fundamental units of heredity that are passed from parent to offspring during reproduction. They are constructed from a segment of deoxyribonucleic acid (DNA) and encode information essential for the construction and regulation of proteins (such as enzymes) and other molecules that determine the growth and functioning of the organism.

A gland is a cell or group of cells which have the ability to manufacture a secretion which acts as a chemical signal or is used by another organ in the organism. Endocrine glands in the human body secrete hormones and discharge these directly into the bloodstream where they are used in other parts of the body. Salivary glands produce saliva in response to eating and sweat glands produce salt and urea in solution to evaporate from the skin to assist the body with temperature control.

Glucose is a simple form of sugar and one of the most important carbohydrates in biological processes. In the human body it is transported by the blood and used as a source of energy in cell function. We maintain a small store of free glucose in our blood (sugar levels) that can be used by cells very quickly as well as a bigger store of chains (polymers) of glucose that we call on during sustained periods of exertion. In plants, glucose is one of the main products of photosynthesis and an important source of chemical energy for plant cellular function as well as for animals that eat plants.

The term glutinous describes a substance that is very sticky and displays similar properties to an adhesive or glue, such as ‘glutinous rice’.

a name given to the southern hemisphere`super continent' consisting of South America, Africa, Madagascar, India, Arabia, Malaya and the East Indies, New Guinea, Australia, New Zealand and Antarctica prior to its break up under the forces causing continental drift.


Hormones are chemicals produced by various glands in the endocrine system which have the effect of changing or controlling the activities of systems or organs in other parts of the body.

a non-metric unit of power. One horsepower is equivalent to 745.7 watts.


Immersion is the act of completely wetting something by allowing it to sink or pushing it below the surface of a liquid.

An ion is an atom or a molecule which becomes charged because of an imbalance of electrons and protons. If the atom or molecule loses a negatively charged electron then its overall charge becomes positive and if it gains an electron then its overall charge becomes negative.


a metric unit of energy. One joule is equal to the energy transformed by the power of one watt operating for one second. 4.184 joule of heat energy (or one Calorie) is required to raise the temperature of 1 gram of water 1°C. There are 3.6 million joule in one kilowatt-hour. The joule is named after an English brewer, James Joule (1818 – 1889), who first quantified the relationship between heat and mechanical energy.


Kilowatt hour
a common unit of energy used for metering electricity. It is equivalent to the use of 1000 watts of electricity for one full hour. 1 kWh = two 500 watt bulbs lit for 1 hour. (10 bulbs x 100 watts each x 2 hours = 2000 watts hours or 2kWh).

Kinetic energy
The term kinetic energy refers to energy attributed to the movement of an object relative to a reference point. The greater the movement and/or the greater the mass of the object the more kinetic energy that can be stored. If an object is stationary then its kinetic energy relative to that point is always zero.  

Other glossaries

Further definitions may be found at the following sites: