Internal Energy, Absolute Zero and the Kelvin Scale
Internal energy is the total kinetic and potential energy of the particles in a body, counted over their random motion rather than the motion of the body as a whole. Absolute zero is where that random kinetic energy is as low as it can go, and the kelvin scale starts there.
What a learner can do afterwards
- Separates internal energy from the kinetic energy of the whole object
- Converts between degrees Celsius and kelvin and explains why a difference is the same size in both
- Says which part of the internal energy changes during melting, when the temperature does not
1 · Read
Internal energy totals the kinetic and potential energy of the particles themselves, counted over their random motion. It never includes the motion of the whole body, so a speeding cold football has no extra internal energy.
Ice melting at zero degrees keeps the same temperature while it melts. The incoming heat breaks bonds instead, raising the potential part while the kinetic part stays flat.
Absolute zero is where random kinetic energy is as low as it can go, and the kelvin scale starts there. Add 273 to a Celsius reading to get kelvin, and note that one step is the same size on both scales.
Write kelvin without the degree sign, as in 298 K. A rise of 10 degrees Celsius is exactly a rise of 10 kelvin, since only the zero points differ.
Internal energy belongs to the particles, and kelvin counts the same steps from absolute zero.
More to read
3.2 Work, Heat, and Internal Energy
Internal energy is the private fortune of the particles: their random kinetic energy plus the potential energy in their bonds. It ignores whether the whole object moves or sits still. A flying ice cube and a resting one at the same temperature hold the same internal energy. Heating raises the jiggling, while melting spends energy loosening bonds at flat temperature.
15.1 The First Law of Thermodynamics
Energy never appears from nowhere: heat in and work done shift the internal store. Warm a gas and its molecules speed up; compress it and you squeeze energy in through work. The first law just balances these books. Absolute zero then marks the floor at 0 K, about minus 273 C, where molecular motion hits its minimum.
14.1 Heat
Heat is energy on the move, flowing from hot to cold until temperatures match. Celsius is handy for weather, but physics counts from absolute zero in kelvin. Converting is one addition: add 273. A one degree rise is identical on both scales, which is why differences never care which you used. Pick kelvin for gas laws and Celsius for the forecast.
Explore more
2 · Watch
به انگلیسیTake it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
13 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.