Definitions Flashcards
Define scaler
Quantity which has size only e.g. distance, speed
Define vector
Quantity which has both size and direction e.g. displacement, velocity
Define displacement
Distance travelled from start; area under velocity-time graph.
Define velocity
Rate of change of displacement; gradient of a displacement-time graph
Define acceleration
The rate of change of velocity; gradient of a velocity-time graph
Define friction
A force which opposes motion
Define newton’s first law
An object will continue to move in a straight line at a constant speed unless an unbalanced force acts on it.
Define newton’s second law
A resultant force will cause an object to accelerate and the acceleration is proportional to the size of the resultant force
Define newton’s third law
To every action force there is an equal and opposite reaction force
Define weight
The force due to the pull of gravity on an object
Define mass
The amount of matter in a body
Define acceleration of free fall, ‘g’
10 m/s², the acceleration of an object allowed to fall freely from rest
Define hooke’s law
The extension of a spring is directly proportional to the applied force, provided that the limit of proportionality is not exceeded
Define spring constant
A measure of the stiffness of a spring; gradient of a force-extension graph
Define principle of moments
In equilibrium the total clockwise moment about a point equals the total anticlockwise moment about the same point
Define centre of gravity
The point through which all the weight of an object appears to act
Define principle of conservation of energy
Energy can be changed from one form to another form but the total amount of energy does not change
Define renewable source
Resource which is naturally replenished within a human lifetime
Define non-renewable source
Resource with a finite supply of energy which will run out some time
Define atomic number Z
The total number of protons in the nucleus of an atom
Define mass number A
The total number of protons plus neutrons in the nucleus of an atom
Define isotope
Different forms of the same element with the same atomic number (and no. of protons) but different mass numbers (and no. of neutrons)
Define radioactive
Unstable nucleus which spontaneously emits radiation
Define background radiation
Radiation detected when no radioactive sources are present
Define ionisation
Changing a neutral atom into a charged ion by removing an electron.
Define half life
The time it takes for half the radioactive nuclei to decay. (Or for the activity to fall to half its original value.)
Define alpha radiation
Same as a helium nucleus; 2 protons and 2 neutrons
Define beta radiation
Fast moving electron from the nucleus
Define gamma radiation
High energy electromagnetic radiation
Define fission
The splitting of a heavy nucleus (by absorption of a neutron) into 2 or more smaller nuclei, a few neutrons and a large amount of energy.
Define fusion
The joining of 2 light nuclei to form a heavier nucleus, releasing a large amount of energy (very high temperature needed)
