Brownian motion:The continuous random motion of solid microscopic particles when suspended in a fluid medium due to the consequence of ongoing bombardment by atoms and molecules.
Bulk's modulus of elasticity:The ratio of normal stress to the volumetric strain produced in a body.
Buoyant force:upward force on an object immersed in fluid.
Abiogenesis: The study of how life on Earth could have arisen from inanimate matter. It should not be confused with evolution (the study of how living things change over time), biogenesis (the process of lifeforms producing other lifeforms) or spontaneous generation (the obsolete theory of complex life originating from inanimate matter on an everyday basis).
Diffuse material orbiting around a central body such as a protostar, a young star, a neutron star or a black hole. Gravitycauses the material in the disc to spiral inwards towards the central body with great speed, and the gravitational forcesacting on the material cause the emission of x-rays, radio waves or other electromagnetic radiation (known as quasars).