Final answer:
A heater warms the air in a room by increasing its temperature, which causes the air molecules to move faster and spread out, decreasing the air density.
Step-by-step explanation:
A heater warms the air in a room by increasing its temperature. When the heater is turned on, it produces heat energy, which is transferred to the air molecules in the room. As the air molecules absorb the heat energy, they gain kinetic energy and move faster, resulting in an increase in temperature.
As the temperature of the air increases, its volume expands. This expansion occurs because the air molecules move away from each other, creating more space between them. The increased volume leads to a decrease in air density, as the same amount of air now occupies a larger space.
For example, if you have a room with a fixed volume and the heater increases the air temperature, the air molecules will move faster and spread out, occupying a larger volume. This expansion causes a decrease in air density.