Science Glossary L - Z
A | B | C | D | E | F | G | H | I | K | L| M | N | O | P | R | S | T | U | V | W
L
Lithosphere
the rigid outer layers of the Earth’s crust and the upper mantle. The tectonic plates are composed of parts of the lithosphere. The lithosphere ranges in thickness from 6-12 km underneath the oceans to more than 200 km under the continents.
M
Magnetic Force
Magnetic forces are examples of non-contact forces that can be easily explored in the classroom. For example, bar magnets experience pushes and pulls without making contact with each other. Strongly magnetic materials include iron, nickel and cobalt, which can exert either attractive or repulsive forces on other similar materials. However all materials are influenced by magnetic fields, but sensitive equipment is needed to detect these effects (such as medical imaging using Magnetic Resonance Imaging - MRI). Magnetic forces are strongly connected to electrostatic forces; the fundamental force of electromagnetism combines both these forces.
Mammals
Mammals are one of the families that make up vertebrate animals. Most mammals give birth to live young which are nourished by milk produced in specialised mammary glands in the female. Mammals are warm blooded and usually have some hair or fur (whales have thick layers of blubber) which assists them to maintain a constant body temperature. An additional characteristic of all mammals is that their heart contains four chambers.
Mass
Mass is best described as a measure of the amount of stuff (or matter) in an object and is very hard to define for students because it is such a fundamental property. To determine the mass of an object you can measure how strongly it is attracted by the Earth's gravitational field (i.e. weigh it on a scale and find its mass). Another method to determine mass, although rarely used in practice, is to measure the object's acceleration when a known force is applied to cause it to accelerate; much bigger forces are required to accelerate a heavily loaded truck compared with a motorbike accelerating at the same rate. Mass is measured in kilograms (kg). The ‘everyday weight’ of an object on the Earth is considered equivalent to its mass simply for convenience; however, this can be a source of confusion in upper levels of school because weight is really a force (see weight force) and should be measured in newtons (N) not kilograms (kg).
Metabolism
In a biological system, metabolism refers to the ongoing interrelated series of chemical reactions taking place in living organisms that provide the energy and nutrients needed to sustain life.
Millennium
A millennium is a period of one thousand years. Millennia is the plural term used to describe a period of many thousands of years.
Mixture
A mixture is the result of combining two or more substances together physically without resulting in a chemical bonding. The components of mixtures can usually be easily separated.
Molecular mass
The molecular mass (less accurately referred to as molecular weight) is equal to the sum of the atomic masses of all atoms in a molecule, based on a scale in which the atomic mass of the carbon 12 isotope is set as being exactly 12.
Molecule
A molecule is formed by the combination of two or more atoms held together by chemical bonds. It may contain combinations of atoms from either the same element or a variety of elements. Unlike the small number of different atoms, there are a huge number of different molecules and the number and type of molecules changes in chemical reactions.
Mutation
Mutations describe any change in the DNA ( deoxyribonucleic acid) contained in a cell. Mutations may be caused by copying errors during cell division, or by exposure to DNA-damaging agents in the environment, such as chemicals or ionising radiation. Some mutations can be harmful, while others may be of benefit to an organism. Mutations in most types of cells are not inherited, however if they occur in sex cells, they can be passed on to offspring and can influence a whole population. The appearance of mutations is central to evolution; if the individual with the mutation is better able to survive and reproduce then the mutation may spread through a population.
N
Naphthalene
Naphthalene is a white crystalline hydrocarbon solid at normal room temperature which passes slowly from the solid state to a gas without becoming a liquid (see sublimation). It is also known as camphor (or moth balls) and is sometimes placed in clothes drawers where it slowly emits a gas toxic to most insects without wetting the clothes.
Natural light source
A natural light source is a luminous object which emits light without any human intervention or control. E.g. the Sun and other stars, fire, lightening, chemical luminescence from glow worms, glow sticks or rotting organic matter and very hot objects.
Nervous system
The nervous system is sometimes referred to as the ‘communication system’ because it coordinates the activity of the muscles, monitors organs, controls input from the senses, and regulates the body's responses to internal and external stimuli. There are two main parts; the central nervous system comprising the brain, spinal cord and retinas and the peripheral nervous system which includes most sensory and muscle connections.
Newton (N) – the unit
The newton is the common unit used for measuring force. It was named in memory of Isaac Newton (1642-1727) who did much to clarify our understanding of forces and motion. Most students and adults have no understanding of the size of a force of one newton (1 N). It is similar to the force needed to support the weight of one apple.
Newton's First Law of Motion
This first law of motion is often stated as: a body remains at rest or in motion with a constant velocity unless acted upon by a net force. This type of language often remains confusing to students unless they are given opportunities to discuss and interpret its meaning using everyday language. It is best considered by an analysis of two situations. The first situation is intuitive. A stationary object will remain stationary unless you provide it with a push or a pull. The second situation is not so intuitive. An object travelling with a constant speed in a constant direction will continue unaltered unless you provide it with a push or a pull. If you do give it a push or pull, it will either change its speed or direction or both. For example, an ice hockey puck experiences minimal friction while moving on the ice and so continues moving at a constant speed in the same direction unless it experiences a push from a hockey stick.
Newton's Second Law of Motion
This second law of motion is often stated as: the resultant force acting on a body results in an acceleration which is in the same direction as the resultant force and is directly proportional to the magnitude of this force and inversely proportional to the mass of the object. This language is very unhelpful to students and does little to improve their understanding of the ideas being expressed. The second law builds on the qualitative understanding of the first law by providing a quantitative relationship between mass, force and acceleration. For expediency it is often taught mathematically as F = ma (where F = force, m = mass and a = acceleration), but although most students learn to successfully manipulate the equation, it does little to assist their understanding of the concepts involved. Consider a description using everyday language. We know that applying a push to an object that is free to move will cause it to accelerate. The second law suggests that doubling the push on the same object will result in twice the acceleration and that the same push given to an object with half the mass will also double its acceleration.
Nuclear reaction
A nuclear reaction involves the collision of individual particles or combinations of particles, or the emission of particles from the nucleus, to form nuclei that are different from the original. This will often result in the production of new elements due to heavy nuclei being broken apart (i.e. nuclear fission) or light nuclei being bonded together (i.e. nuclear fusion). The vast majority of nuclear reactions occur in stars where the extremely high temperatures encourage high energy collisions between nuclei to create new elements. Students often consider nuclear reactions to involve similar processes to chemical reactions, but new elements can never be created by chemical reactions.
O
Ohm
An ohm is a unit of electrical resistance named in honour of Georg Ohm (1789 -1854), a German scientist who started to investigate the properties of electrical resistance while teaching as a high school physics teacher. He is recognised for discovering the relationship between voltage, current flow and resistance known as Ohm’s Law.
Oobleck
Oobleck is a popular name used to refer to a stiff mixture of corn starch and water (1 part water to 1.5-2 parts corn starch) often used as a demonstration aid when teaching about the properties of solids and liquids. Oobleck is not readily categorised as a liquid or solid as it behaves as a ‘runny’ liquid if poured slowly but behaves much like a solid if forced to move or change shape quickly. Substances which display similar behaviour are called ‘dilatants’. The name Oobleck originates from a green slime invented by children's author Dr Seuss in the book Bartholomew and the Oobleck.
Orbit
For most students the term orbit generally refers to the path taken by an artificial satellite around the Earth, for example, the International Space Station orbits around the Earth. However the term refers generally to the path taken by both artificial and natural satellites around any central object under the influence of gravity. Hence the moon orbits the Earth and the Earth orbits the sun. Most orbits are described as being circular but are more precisely an ellipse.
Organism
An organism is a living thing composed of either a single cell or multiple cells that has (or can develop) the ability to act or function independently. Five forms of organisms are often proposed: plants, animals, fungi, protists (such as algae) and bacteria. Organisms are the smallest biological unit needed for reproduction, so while a single cell organism such as bacteria may be autonomous, the majority of individual cells in multicellular organisms are not. This means that, while many individual cells in an organism that has recently died may be carrying on their metabolic processes, the organism is regarded as dead.
P
Particle model of light
This model suggests light is composed of huge numbers of tiny particles which are emitted from a light source and travel outward independently in straight paths in all directions.
Peer review
This is a public process that requires peers – other scientists – to accept ideas or reject ideas in a consensus making process. In this consensus making it will mean that some scientists will agree, some will partially agree and others will disagree. In reaching a consensus, there may be some modification of the ideas presented. For example, when proposing a theory such as ‘Natural Selection’ it is impossible to ‘prove’ or ‘disprove’ the theory, but rather it may be supported, rejected or modified.
Photosynthesis
Photosynthesis is the process used by plants, algae and some bacteria to change carbon dioxide and water into carbohydrates using energy from sunlight. The process usually releases oxygen into the atmosphere as a by-product. A common misconception by students is that green plants require only carbon dioxide and that all the oxygen they produce during photosynthesis is a net gain for the atmosphere. Plants also require some oxygen for respiration.
Physical environment
The physical environment refers to the external, tangible surroundings in which an organism exists and which can influence its behaviour and development. It includes landforms, soil types and climate.
Plasma
In biological systems the term plasma is used to describe the liquid component of blood in which the blood cells and the proteins that form blood clots are suspended. Plasma is a yellow coloured fluid and the largest single component of blood, making up about 55% of total blood volume.
In physics the term plasma is often used to refer to a fourth state of matter in which a substance is in the form of a super heated gas.
Plastic flow
The slow deformation of a material’s shape due to the continued application of a force allowing it to change shape by bending without fracture or decomposition.
Polymerisation
Polymerisation is a chemical reaction in which two or more small molecules are combined to form much longer connected chains ( polymers) of repeated molecules.
Population
In biological systems a population refers to a collection of organisms of a particular species living and interacting in the same geographic region.
Potential energy
The energy possessed by an object by virtue of its location or position in a field. As an example, consider a gravitational field. The higher an object is when compared with another, the greater its gravitational ‘potential’ energy. This gravitational energy is converted into kinetic energy (energy of motion) as it falls. An object which is distorted (compressed or stretched) also has potential energy.
Power
Is the rate at which energy is transformed. It is usually measured in the international unit called the watt and occasionally with the unit horsepower when concerned with cars or electric motors.
Precipitation
In the chemical sciences, precipitation refers to the formation (condensation) of a solid from a solution during a chemical reaction. Commonly two dissolved substances react to form a new substance that does not remain in solution. The precipitate usually settles out of solution on the bottom of the container but can form a suspension or colloid. During these changes, the solution changes from being translucent to opaque (i.e. ‘clear’ to ‘cloudy’).
Private science
The ideas and understanding scientists have about science as they go about their daily work.
Producer
The term producer is used in biology to describe an organism, generally a plant or algae, that can produce organic food molecules (usually glucose) using the sun's energy (by photosynthesis) or by other chemical reactions (chemosynthesis). Most producers are a source of food for other organisms.
Product
This term is used to describe the substances that are produced by a chemical reaction. Reactants undergo a chemical change to produce products with different properties.
R
Reactants
A term used to describe the substances that take part in a chemical reaction. The reactants undergo a chemical change to produce products with different properties.
Reliability
Reliability is the degree to which an assessment instrument or protocol consistently and repeatedly measures an attribute achieving similar results for the same population.
Renal System
The renal system is responsible for the regulation of bodily fluids and the elimination of wastes from the human body. The key organs of this system are the kidneys which filter wastes (such as urea) from the blood and excrete them, along with water and other waste, as urine. The body is able to regulate the operation of a number of organs to help it adapt and accommodate to changes in environmental conditions that may adversely affect body functions. The kidneys play a vital role in this process by regulating acid-base balance, electrolyte concentrations and blood pressure and controlling blood volume.
Respiration
Respiration is a process with both physical and metabolic aspects, whereby an organism exchanges oxygen and carbon dioxide with its external environment. It is this exchange of gases that allows an organism to supply its cells and tissues with the oxygen needed for metabolism and relieves them of the carbon dioxide formed in energy-producing chemical reactions.
S
Selection
Selection is the process where organisms with advantageous traits are more successful reproductively than those without the traits. This results in them producing more offspring to succeeding generations which have an increased chance of expressing a similar trait. Selection can occur from the pressures of natural environmental conditions or from human intervention in selective breeding programs.
Solar system
The solar system is usually thought by students to be just the planets in orbit around the sun, but it also includes all the moons, periodic comets, meteors, asteroids, dust and debris which are held in orbit by the sun's gravitational attraction. The solar system is far bigger than the orbit of the outermost planet.
Solution
A solution is formed by combining one or more substances by dissolving them into another substance. A common example would be a solid (solute) dissolving into a liquid (solvent), like salt into water. Gases may also dissolve into liquids, like carbon dioxide or oxygen in water, and liquids and gases into themselves.
Solvent
A solvent is the substance doing the dissolving that results in a solution. Water is a good solvent for many, but not all substances. In everyday speech, the term solvent is sometimes used for non-aqueous liquids such as turpentine and acetone that are useful for dissolving substances such as oil that cant be dissolved in water.
Spring balance
A spring balance is a common laboratory device used to measure the weight of an attached object by recording the resulting extension or stretching of a steel spring. The spring extension is proportional to the stretching weight force so it can be calibrated to measure either force in newtons (N) or equivalent mass in kilograms (kg).
Stalactites
The word stalactites comes from the Greek word for ‘drip’ and means ‘that which drips’. Stalactites are a type of thin cone-shaped rock formation that hangs from the ceiling or roof of limestone caves. They are usually produced by the deposition of minerals from solution as it drips.
Stalagmites
Stalagmites are a cone-shaped rock formation found on the floor of a cave that are usually but not always found below a stalactite. Stalagmites are usually produced by the deposition of minerals from solution from the drips falling from above.
Star
The term star has many everyday meanings. When used to describe an astronomical object, it generally refers to massive spherical balls of very hot gas that are visible in the night sky as only points of light due to their immense distances. Stars are so massive that the compression of their gases by gravity initiates sustained nuclear reactions which result in the production of new elements and the release of energy in the form of light and heat.
Subduction
The term subduction describes the movement of the Earth’s tectonic plates where one plate collides with another forcing one plate to ride up over the other. The plate forced below usually suffers considerable melting as it is forced deep below the Earth’s surface.
Sublimation
Sublimation is the physical change of state of a substance from a solid to a gas without passing through the liquid state or the reverse process of passing from a gas to a solid. Examples of substances that sublime at room temperatures are carbon dioxide (dry ice), iodine and naphthalene (camphor or moth balls). In conditions of low humidity, ice will sublime directly to water vapour at temperatures below 0 degrees Celsius.
Synthetic
The term synthetic refers to a substance that has been manufactured, processed or chemically altered after being extracted from naturally occurring plant, animal or mineral sources. The term is not usually applied to substances produced by naturally occurring biological processes.
T
Tectonic plates
rigid parts of the Earth's crust and upper mantle that move very slowly and adjoin each other along zones of seismic activity. These plates form a part of the lithosphere.
Trace elements
The term trace elements is used to describe a range of chemical elements that occur in very low concentrations which are vital for the growth, development and physiology of plants.
U
Urea
Urea is a product of protein breakdown that can be safely removed from the body. Urine is the waste solution that contains dissolved urea. An average person excretes about 30 grams of urea per day. The ability of the liver to convert products of protein breakdown into urea is essential to human health.
V
Validity
Validity is the state of being authentic or genuine. Validity describes the extent to which a test measures the skills it intends to measure and the extent to which inferences and actions made on the basis of this assessment are appropriate and accurate.
Veins
A vein is a blood vessel in the body that returns blood from organs toward the heart. Most veins carry blood with small amounts of dissolved gases, but the pulmonary veins carry blood rich in oxygen from the lungs to the heart. Because the pressure of the heartbeat is dissipated in the capillaries, veins do not have elastic walls; they are essentially hollow tubes that collapse when not filled with blood and have one-way flaps called ‘venous valves’ to prevent gravity from causing blood to backflow and pool in the lower extremities of the body. Veins rely on pressure from adjacent contracting muscles to push the blood back to the heart.
Vertebrates
Vertebrate is a term commonly used to describe animals that have backbones or spinal columns. The name comes from the bones of the spinal column, the vertebrae. Vertebrates contain many familiar groups (families) of large animals such as reptiles, birds, mammals, fish and amphibians. This group is characterized by a muscular system as well as a central nervous system. Vertebrates are most easily distinguished by having an easily identified head, with sensory organs (especially eyes concentrated at the fore end of the body. In comparison some examples of animals that do not fit this category (invertebrates) are jellyfish, worms and insects.
W
Watt
The watt is a metric unit of power equal to the rate of transformation of one joule of energy per second. It is named after the Scottish engineer and inventor James Watt (1736-1819) who did much to develop and popularize the steam engine.
Wave model of light
This model suggests light is composed of continuous waves which travel outwards from the light source much like water waves radiate from the impact of a stone thrown into a pond.
Weight force
Weight is often confused with mass, but it is not the same thing. The weight of an object on Earth is the gravitational force of Earth acting on the object and will vary depending on the position of the object and the strength of Earth's gravitational field. The weight of an object will change if it is placed on the surface of a different planet because the gravitational force of that planet on the object will be different, but the object's mass (i.e. the amount of matter it contains) remains the same. Weight is what a scale reads and is measured in newtons (N).
Work
The word work is often used in everyday speech with a variety of meanings. To the scientist the word ‘work’ is used with a very precise meaning. It defines a mathematical measure of the ‘effort’ needed to move an object by applying a force to it. The work completed is a product of the force applied to the object and the resulting distance it was moved. If an object is not moved by a ‘push’ or ‘pull’ then no work has been done.
Other glossaries
Further definitions may be found at the following sites: