{"id":464,"date":"2026-07-12T01:38:17","date_gmt":"2026-07-12T01:38:17","guid":{"rendered":"https:\/\/physicsfundamentalsinfo.com\/blog\/?p=464"},"modified":"2026-07-12T01:38:19","modified_gmt":"2026-07-12T01:38:19","slug":"charles-law","status":"publish","type":"post","link":"https:\/\/physicsfundamentalsinfo.com\/blog\/mechanics\/charles-law\/","title":{"rendered":"Charles’s Law Explained"},"content":{"rendered":"\n
Definition<\/div>

\nCharles law, properly written Charles’s law, states that the volume of a fixed mass of gas held at constant pressure is directly proportional to its absolute temperature. Double the temperature in kelvin and the volume doubles. In symbols, V\u2081 divided by T\u2081 equals V\u2082 divided by T\u2082, with T always in kelvin.\n<\/p><\/div>\n\n

Leave a balloon in a hot car and it strains at the knot, taut and glossy. Bring it out into a cold night and within minutes it sags, wrinkled, looking half-empty.<\/p>\n\n

Nothing leaked. The same air sits inside, pressed by the same atmosphere \u2014 only the temperature moved, and the volume obediently followed. That is Charles’s law, doing its work in a car park.<\/p>\n\n

What Is Charles’s Law?<\/h2>\n\n

Ask a class what heat does to a gas and someone will say “it makes it expand.” True. But that is a description, not a law \u2014 and a law has to tell you exactly how much<\/em>.<\/p>\n\n

Charles’s law supplies the number. Hold the pressure steady, keep the same quantity of gas, and the volume tracks the absolute temperature in strict proportion. Ten per cent hotter in kelvin means ten per cent bigger, every time.<\/p>\n\n

That proportionality only works if you measure temperature from the right zero. Start counting at absolute zero, in kelvin, and the relationship is a clean straight line through the origin. Start at the freezing point of water, in Celsius, and it falls apart completely.<\/p>\n\n

Two conditions do the heavy lifting here, and both are easy to lose sight of:<\/p>\n\n