* Thermal Expansion: When you heat a substance, the particles within it gain kinetic energy and move faster. This increased movement causes them to spread out and occupy a larger volume.
* Density Calculation: Density is defined as mass per unit volume (Density = Mass / Volume). Since the mass of the substance remains constant, but the volume increases due to expansion, the overall density decreases.
Why not all substances?
While most substances experience thermal expansion, there are exceptions. For example:
* Water: Water is an anomaly. Its density increases as its temperature rises from 0°C to 4°C, and then decreases with further temperature increase. This unusual behavior is due to the unique structure of water molecules and the way they interact with each other.
* Some alloys: Certain metal alloys can exhibit a decrease in density with increasing temperature due to complex interactions between the constituent metals.
In summary, the decrease in density with temperature for most substances is a direct consequence of thermal expansion, where the increased kinetic energy of particles leads to a larger volume, while the mass remains constant.
