Thermal energy moves from hot to cold — Physics, 11–13 years
Temperature differences make thermal energy spread until objects and surroundings become closer in temperature.
Hot to cold
Thermal energy moves when two things have different temperatures. It naturally travels from the warmer thing to the cooler thing, not the other way round. A hot mug warms your hands, while an ice cube cools a drink, until the temperature difference becomes smaller.
Why does a drink cool?
People wanted to explain why hot food cools and why houses lose warmth in winter. The key problem is that temperature is not a substance that leaks away; moving particles transfer energy through contact, moving fluids or radiation. Insulation works by slowing these transfers.
A metal spoon in soup
Put a metal spoon in soup at 80 °C and leave its handle outside. First, the end in the soup receives energy from the hot liquid. Next, energy passes through the metal to cooler parts of the spoon. Finally, the handle becomes warm enough to feel hot; removing it or using a wooden spoon reduces the transfer to your hand.
Cold does not flow into things
It is reasonable to say that a cold drink gets cold air inside it, because we often describe cold as if it were a thing. In physics, thermal energy leaves the warmer drink and moves to the cooler surroundings. A fridge does not create cold; it removes thermal energy from inside.
Keeping homes warm
Thermal transfer explains coats, oven gloves, double glazing and wall insulation. Wool and trapped air slow energy moving away from your body, while a metal pan transfers energy quickly to food. Engineers choose materials according to whether they want heat to move quickly or slowly.
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