Tettheten

Tettheten is the concept of density, a measure of how much matter or how many points occupy a given space. It is used across physics, chemistry, geology, biology, and mathematics to describe how tightly packed a substance or a set of points is.

In physical contexts, density is defined as mass per unit volume, ρ = m/V, with the SI unit kilograms per cubic meter (kg/m^3). Density is an intrinsic property that can vary with temperature and pressure and differs between substances. For liquids and solids, density helps identify materials and predict buoyancy, while for gases it changes markedly with changes in state conditions.

Other common uses include population density, which expresses the number of people per unit area (for example, per square kilometer), and number density, which counts particles such as molecules or atoms per unit volume. In materials science, distinctions are made between bulk or apparent density (including pore spaces) and true or real density (excluding voids).

In mathematics, density has a theoretical meaning: a subset of a space is dense if every point of the space can be approximated arbitrarily well by points from the subset; equivalently, the closure of the subset equals the whole space. A classic example is the rational numbers being dense in the real numbers.

Tettheten thus describes how packed something is, whether a physical material, a population, a collection of particles, or a mathematical set, and it provides a basis for comparing, measuring, and modeling diverse phenomena.