Heat Transfer
Heat transfer is the movement of heat from something warm to something cooler, like an oven warming food inside it.
A warm pan sits on a cool countertop. Heat moves from the hot pan down into the counter. The pan slowly cools as the counter warms up. Warm always flows toward cool until both feel the same.
Explaining heat transfer by grade level
When you bake a custard, the oven is hot and the egg mix is cold. Heat moves from the hot oven air into the cold mix. The egg mix gets warmer and warmer. That moving heat is what cooks the custard and makes it firm.
Projects that explore heat transfer
Baking surrounds a potato with hot oven air, which moves steadily inward from the surface. Steaming works the same way — hot vapor touches cooler food and transfers energy into it. Microwaving does the same job in a fraction of the time. In this experiment you cook potatoes and carrots using several methods, then compare weight, taste, and texture to see how the rate of heat transfer changes the result.
Dark colors absorb sunlight while light colors reflect it — and that difference shows up fast. When you place a black bottle and a white bottle in bright sunlight, the black surface pulls in the sun's energy and warms the air inside. As that air heats up, it expands and inflates the balloon stretched over the mouth. The white bottle reflects most of that energy away, so the air inside stays cool and the balloon on top remains flat.
Heat moves from a warm lamp to cooler water nearby. You place both jars at the same distance from a light source. After an hour, you measure the temperature of the water to see how much warmth moved in.
A parabolic curve reflects light toward a single focal point, concentrating the sun's energy in one spot. When you line that curve with aluminum foil and aim it at the sky, the bright spot at the focal point gets hot enough to cook food. Place a skewer through that focal point and the heat moves from the concentrated sunlight directly into a hot dog — no stove required.
Hold an air-filled balloon over a candle and it pops almost immediately. Fill a balloon with half a cup of water first, and the result is completely different. Water absorbs heat from the flame through conduction — warmth moves from the hot surface into the cooler water inside. That constant flow of energy away from the rubber keeps it from ever getting hot enough to burst.
When a burning nut sits beneath a test tube of water, heat moves from the flame into the cooler water above it. You mount a peanut and a cashew on paper clips, light each one, and measure the rise in water temperature after one minute of burning. Combined with the weight the nut lost, those numbers let you calculate the calories released per gram — a simple version of calorimetry. In this test, the cashew stored more energy per gram than the peanut.