---
title: "Internal Energy, Absolute Zero and the Kelvin Scale"
description: "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"
canonical: https://lightmysky.com/learn/science/internal-energy-absolute-zero-and-the-kelvin-scale-mt_n4Ku8ZDy1U
source: https://lightmysky.com/learn/science/internal-energy-absolute-zero-and-the-kelvin-scale-mt_n4Ku8ZDy1U.md
retrieved: 2026-09-12
---

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# 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.

Subject: Science · Area: Energy · Ages 16 to 17
Page: https://lightmysky.com/learn/science/internal-energy-absolute-zero-and-the-kelvin-scale-mt_n4Ku8ZDy1U

## Ready when they can

- 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

## Lesson: Inside heat: particles and kelvin

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.

**Example.** 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.

**Tip.** 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.

**Recap.** Internal energy belongs to the particles, and kelvin counts the same steps from absolute zero.

## Practice

13 questions on this page, each with its working shown.

## Needs first

- [Specific Heat Capacity as a Material Property](https://lightmysky.com/learn/science/specific-heat-capacity-as-a-material-property-mt_mXC9IKom3P)
- [Kinetic and Gravitational Potential Stores](https://lightmysky.com/learn/science/kinetic-and-gravitational-potential-stores-mt_uD3jklaZCw)

## Opens up

- [Specific Heat Capacity and Specific Latent Heat in Calculations](https://lightmysky.com/learn/science/specific-heat-capacity-and-specific-latent-heat-in-calculations-mt_GKNPAJgroW)
- [The First Law of Thermodynamics for Any Process](https://lightmysky.com/learn/science/the-first-law-of-thermodynamics-for-any-process-mt_LIWgeWSXHz)