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By the end of these notes, you should be able to:
Thermal energy is the energy that an object or region possesses because of its temperature. The hotter something is, the more thermal energy it has.
Think of thermal energy like water in a tank — it always flows from the higher tank to the lower one. In the same way, thermal energy always flows from the hotter place to the cooler place.
When two regions are at different temperatures and are placed in contact with each other, thermal energy flows from the hotter region to the cooler region. This always happens — it is a fundamental rule of nature.
Important: Energy is never created or destroyed — it is simply transferred from one place to another. This is called the conservation of energy.
Imagine holding a hot mug of coffee. The coffee is very hot, and your hands are much cooler. Thermal energy flows from the hot coffee → into the mug → and then into your cooler hands. That is why your hands feel warm. The coffee slowly gets cooler as it loses energy to everything around it.
When you place a thermometer into boiling water, the thermometer starts off much cooler than the water. Thermal energy flows from the hot water into the cooler thermometer. As this happens, the thermometer reading rises — it is gaining energy and warming up. Eventually, the thermometer reaches the same temperature as the water and stops changing.
When you drop ice cubes into a glass of room-temperature water, many students think the ice makes the water cold. But what actually happens is the opposite — the water (which is warmer) transfers thermal energy to the ice (which is colder). The ice absorbs this energy and melts. The water loses energy and gets cooler. They both move toward the same final temperature.
Common Misconception: Cold does not "travel" into the water. There is no such thing as a flow of coldness. Only thermal energy flows — and it always flows from hot to cold.
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