Physical Quantities and Measurement: Density and Flotation

A set of vocabulary flashcards based on the lecture notes regarding density, its measurement, relative density, and the physics of flotation.

Density

The mass per unit volume of a substance, which is a measure of how tightly matter is packed in it.

SI unit of density

$\text{kg/m}^3$ (kilograms per cubic meter).

CGS unit of density

$\text{g/cm}^3$ (grams per cubic centimeter).

Eureka can

A cylindrical container with a spout positioned below the top used to determine the volume of irregular solids by measuring displaced water; also known as a displacement vessel or overflow jar.

Relative density (RD)

The ratio of the density of a substance to the density of water at $4\,^{\circ}\text{C}$. It is a dimensionless quantity.

Specific gravity

Another term used for relative density.

Relative density bottle

A special glass bottle with a capillary-tube stopper used to determine the relative density of liquids by ensuring a fixed volume of liquid is measured.

Hydrometer

An instrument used to measure the relative density of liquids, consisting of a weighted glass bulb and a graduated stem.

Lactometer

A specific type of hydrometer used to test the purity of milk.

Plimsoll lines

Markings on the hull of a ship that indicate the maximum level to which the vessel can be safely submerged in different types of water and seasons.

Immiscible liquids

Liquids that do not mix with each other; when mixed, the liquid with the lower density will float on top of the liquid with the greater density.

Convection currents

Currents set up in liquids and gases caused by differences in densities between different layers due to temperature changes.

Mercury

A metal that is liquid at room temperature and has a larger density ($13.6\,\text{g/cm}^3$) than many solids.

Dead Sea

A body of water located between Jordan and Israel with such high salt concentration and density that objects and people cannot sink in it.

Variation of density with temperature

The principle that density decreases as temperature increases (due to volume expansion) and increases as temperature decreases (due to contraction), while mass remains constant.