Heat Energy EP – 2
8 Minutes
Heat energy and temperature for kids: learn how thermometers work, boiling points, thermal equilibrium, and heat flow. A science lesson in English.
- Using a thermometer and temperature units like Celsius and Kelvin
- Measuring the boiling point of water at 100 degrees Celsius
- Heat flow, thermal equilibrium, and how molecule count affects heat
What this lesson teaches
Heat energy is the energy transferred between materials due to temperature differences, while temperature measures how hot or cold an object is. Heat naturally moves from warmer matter to cooler matter until both reach the same temperature.
Measuring temperature and units
A thermometer is a tool used to measure the temperature of any matter. For example, placing a thermometer under the tongue reveals whether body temperature is normal or elevated by a fever. Celsius is a common temperature unit, just as meters measure length and kilograms measure mass. Two other global temperature units are Fahrenheit and Kelvin, with Kelvin serving as the official SI unit for temperature.
The boiling point of water
When water is heated, its temperature continuously rises until it hits 100 degrees Celsius. At this temperature, the water stops increasing in temperature and transforms into vapor that escapes into the air. The temperature at which liquid water turns into vapor and escapes is known as the boiling point of water, which is 100 degrees Celsius.
Heat flow and thermal equilibrium
- Heat energy naturally flows from an object at a higher temperature to an object at a lower temperature.
- When hot water at 80 degrees Celsius mixes with cooler water at 20 degrees Celsius, heat transfers between them.
- The heat flow continues until all the water reaches the exact same temperature.
- The balanced state where two matters reach the same temperature and heat flow stops is called thermal equilibrium.
How molecule count affects heat
Heat energy does not depend solely on temperature, but also on the number of molecules present in a substance. A small glass of water heats up quickly to 70 degrees Celsius because it contains only a small number of molecules. In contrast, a large vessel filled with water needs much more heat energy to reach 70 degrees Celsius because it contains far more molecules. For this reason, a large bucket of water at 40 degrees Celsius contains more total heat energy than a small glass of water at 70 degrees Celsius.