Specific gravity is the ratio between the substance's density and the density of water. Being a ratio of dimensions with same units of measure, this value is unitless.
The substance or objects sinks in water if its density is greater than that of water. On the other hand, it floats if its density is lesser compared to that of water.
Having said so, the substance or object sinks in water if the specific gravity is greater than 1 and floats if the specific gravity is lesser than 1.
sinks: SG > 1
floats: SG < 1
If you and the source of sound are moving apart, then the pitch (frequency) <em>you hear</em> is <em>lower</em> than the pitch (frequency) that's actually leaving the source.
It doesn't matter whether you or the source is the one moving, only that the distance between you is increasing.
Electrons are located outside the nucleus
Decreases, stays the same, increases.
The volume decreases because as air is cooled, the individual molecules collectively possess less kinetic energy and the distances between them decrease, thus leading to a decrease in the volume they occupy at a certain pressure (please note that my answer only holds under constant pressure; air, as a gas, doesn't actually have a definite volume).
The mass stays the same because physical processes do not create or destroy matter. The law of conservation of mass is obeyed. You're only cooling the air, not adding more air molecules.
The density decreases because as the volume decreases and mass stays the same, you have the same mass occupying a smaller volume. Density is mass divided by volume, so as mass is held constant and volume decreases, density increases.
