Light and heat
How energy travels, and why appearances and touch can mislead us.
- Why does tile feel colder than carpet? Tile can take heat from your skin faster than carpet does, even when both have the same temperature. Your sense of cold reflects the rate of heat transfer as well as temperature.
- Why does warm water rise in a pot? Water warmed near the bottom of a cooking pot can become less dense than the cooler water above. Buoyancy makes it rise, setting up circulation that carries heat.
- How can a fire warm you without touching you? A fire emits electromagnetic radiation that your skin can absorb. This transfers energy across the space between you and the fire without requiring hot air to carry it.
- Why can glass almost disappear in oil? If a glass object and its surrounding oil have closely matched refractive indices, light changes direction very little at their boundary. That removes an important visual clue to the glass's outline.
- Why is the sky blue? Molecules in the atmosphere scatter shorter visible wavelengths more strongly than longer ones. This sends blue light toward us from across the sky; our eyes' sensitivity also shapes the color we see.