Charles's Law, discovered by French scientist Jacques Charles in 1787, describes the relationship between the volume and temperature of a gas at constant pressure. It states that when the pressure on a sample of a dry gas is held constant, the volume of the gas is directly proportional to its absolute temperature. This means that as temperature increases, the volume of the gas increases proportionally, and as temperature decreases, the volume decreases.

This law is fundamental to understanding gas behavior in thermodynamics and has numerous practical applications. It explains why hot air balloons rise (heated air expands and becomes less dense), why tires can become overinflated on hot days, and why weather balloons expand as they rise through the atmosphere to colder regions. The law assumes ideal gas behavior, which is a good approximation for most gases at normal temperatures and pressures.

When using Charles's Law, it's crucial to use absolute temperature (Kelvin) rather than Celsius or Fahrenheit. This is because the proportional relationship only holds when measured from absolute zero. The conversion from Celsius to Kelvin is straightforward: simply add 273.15 to the Celsius temperature. Using Celsius directly would give incorrect results because the zero point of the Celsius scale is arbitrary.

Charles's Law assumes ideal gas behavior and constant pressure conditions. Real gases may deviate from this law at very high pressures or very low temperatures, where intermolecular forces become significant. For most everyday applications and laboratory conditions, however, Charles's Law provides an accurate description of gas behavior.