M

mach - scale used for speed compared with the speed of sound. Mach 1 = speed of sound
machine - a device that makes work easier, reduces the effort but not the work
macroscopic - large scale, not down to microscopic level.
magdeburg hemispheres - apparatus made of two hemispheres used to demonstrate air pressure
Magellanic clouds - two irregular galaxies visible with the naked eye from the Southern Hemisphere
magnetic moment - couple exerted on a magnet when placed at right angles to a unit uniform field
magnetic flux - produce of the area of a surface and the magnetic flux density normal to that area
malleable - material that can be beaten into a flat shape e.g. gold to gold leaf
manometer - instrument for measuring pressure using liquid columns (U tube)
mantle - layer in the structure of a planet between its crust and its core
maria - smooth, darker area on the Moon. Named seas or 'maria' (singular mare)
Mars - fourth planet from the Sun.
martian - referring to Mars
mass - the amount of matter in a body. Measurement of the inertia of a body. Unit kg.
magnadur - highly magnetic ceramic material use for magnets
magnetic field - region round a magnet affected by the magnet
magnetometer - instrument for comparing magnetic fields
magnetron - electron tube used in the development of radar. Now used to find e/m.
magnification - image size/object size in an optical instrument (linear magnification)
magnitude - size
magnitude scale- scale of brightness of astronomical objects (lower numbers are fainter)
major axis - the longest axis of an ellipse
mass defect - mass equivalent of the binding energy in a nuclear process
mass-energy equation   E = mc², m the mass of the particle and c the speed of light
material - substance
mean - the average of a series of values
mean free path - the mean distance that a molecule moves between collisions
mean square velocity - the mean of the sum nc² (Snc²), n is the number of molecules and c their velocity
mechanical advantage - in a machine, the ratio of the load to the effort
Mega (M) - one million
Megahertz - one million vibrations per second (MHz)
Mercury - a rocky, cratered planet nearest to the Sun
Mercury - name of the first manned US space craft
MeV - one million electron volts
melting point - temperature at which a substance changes from a solid to a liquid
meniscus - the curved shape of a liquid surface, maybe be concave or convex
meniscus lens - a concavo-convex or convexo-concave lens
meridian - at a point on the Earth, a great circle passing through the poles and that point
meson - subatomic particle lighter than a proton and made of a quark and an antiquark
Messier catalogue - catalogue of nebulae and galaxies first published in 1774
metamorphic rock - rocks that have been buried and then changed by pressure and/or heat
meteor - streak of light seen in the sky when a meteorite burns up
meteorite - lump of rock that burns up as it falls through the Earth's atmosphere
meter - a device for measuring something
meter - US spelling for metre
metre - basic unit of measurement of length (100 cm, 0.001 km)
MHD - magnetohydrodynamics
Michelson-Morley experiment - an experiment to test (and then eject) the existence of the ether
micro - one millionth
micron - 10^-6 m
microamp - one millionth of an amp
microchip - a chip of semiconductor on which have been etched a number of circuits
micrometer - device for measuring small distances to within 1/100 mm
microphone - device for converting sound energy into electrical energy
microscopic - very small
microwaves - waves used for communication and cooking. Wavelength less than radio.
Milky Way - band of stars visible form Earth - the view along the plane of the galaxy
milli - one thousandth, as in millimetre (mm)
milliamp - one thousandth
minimum deviation - the smallest possible deviation of a given light ray by a prism
minor planet - asteroid, orbits generally between Mars and Jupiter
Mir - Russian space station
Mira - member of a class of long-period variables
mirage - image of the sky due to reflection in hot air near the ground
Miranda - moon of Uranus, thought to have been destroyed and then reformed
modem - abbreviation for modulator-demodulator, connecting computers to a telephone line
moderator - material (graphite or heavy water) used to slow down fast neutrons in a reactor
modulation - changing the shape or size of one signal (wave) by using another
modulus of elasticity - the ratio of stress over strain
moiré fringes - a pattern of dark areas formed by overlapping pairs of patterns of lines
molar - amount of a substance
molecule - the smallest particle of a compound – composed of two or more atoms
moment - turning effect of a single force (= Force x distance of force from pivot)
moment of inertia - the reluctance off a body to change its rotational motion (Smr²)
momentum - mass x velocity
monochromatic - one colour, as in laser light, made of a single wavelength.
monomode - fibre optic made of a single fibre of uniform nature
monostable - a circuit that has only one stable state
MRI - magnetic resonance imaging – a way of scanning the body using magnetic fields
multipath dispersion - the spreading of a pulse due to slightly different paths down an optical fibre
multimeter - a meter that has many ranges, current, voltage resistance, decibel level etc.
muons - elementary particles created in the upper atmosphere by cosmic rays
myopia - defect of the eye. Near sighted or short sighted. Can only see nearby objects