Mass per unit volume is called ….. of a substance. A. Specific Gravity B. Density C. Gravity D. None of these
The Correct Answer and Explanation is:
The correct answer is B. Density.
Density is defined as the mass per unit volume of a substance. It is a fundamental physical property that describes how much mass is contained in a given volume. Mathematically, density (ρ) is expressed as: ρ=mV\rho = \frac{m}{V}ρ=Vm
Where:
- ρ\rhoρ is the density,
- mmm is the mass, and
- VVV is the volume.
The unit of density in the International System of Units (SI) is kilograms per cubic meter (kg/m³), though in practical contexts, it can also be expressed in grams per cubic centimeter (g/cm³).
Importance of Density:
- Identification of Materials: Density helps in identifying substances, as each material has its own unique density. For example, lead is denser than aluminum, which is why a lead object feels heavier for its size.
- Buoyancy: The density of an object plays a crucial role in determining whether it will float or sink when placed in a fluid. An object will float in a fluid if its density is less than the density of the fluid. For instance, oil floats on water because oil has a lower density than water.
- Temperature and Pressure Effects: The density of most substances changes with temperature and pressure. For example, when a gas is heated, its molecules spread apart, causing its density to decrease. Similarly, when a gas is compressed, its density increases.
Other Choices:
- Specific Gravity (A): This is a ratio of the density of a substance to the density of a reference substance (usually water). It does not have units because it is a dimensionless quantity. Specific gravity is used to compare the relative densities of substances.
- Gravity (C): This refers to the force that attracts objects towards the center of the Earth or other celestial bodies. It is not related to mass per unit volume.
Thus, density is the correct term to describe the mass per unit volume of a substance.
