Hulkühikud

Hulkühikud, also known as mass units, are a fundamental concept in physics and chemistry used to quantify the amount of matter in an object. They are distinct from concepts like volume, which measures the space an object occupies, or density, which relates mass to volume. The most common hulkühik used internationally is the kilogram, defined by the International System of Units (SI).

The kilogram is one of the seven base units of the SI system. Historically, it was defined as the mass of a specific platinum-iridium cylinder kept in France. However, as of 2019, the kilogram is defined based on the fixed numerical value of the Planck constant, a fundamental constant of quantum mechanics. This redefinition ensures that the kilogram is based on universal physical constants rather than a physical artifact, making it more stable and reproducible.

Other common hulkühikud include the gram, which is one-thousandth of a kilogram, and the tonne (or metric ton), which is equal to 1000 kilograms. In scientific contexts, especially in chemistry, the mole is a crucial hulkühik that represents a specific number of entities (like atoms or molecules), known as Avogadro's number. The concept of mass is crucial for understanding inertia, gravitational force, and energy.