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📘 How does a thermos keep things hot

Follow heat through conduction, convection, and radiation, then open a thermos layer by layer to see how a vacuum, reflective surfaces, a narrow neck, and a careful lid slow its escape.

3
lessons
~15 min
to learn
Adults
level
Start the course →

What you’ll learn

  1. Heat is always looking for a way outDistinguish conduction, convection, and radiation as routes by which a hot drink loses energy.A thermos slows three kinds of heat transfer rather than creating heat or freezing time.
  2. The bottle is a map of the heat pathsRead the double wall, vacuum, reflective surface, supports, and lid as parts of one thermal design.The bottle's shape reveals which heat paths engineers remove, reflect, narrow, or seal.
  3. A laboratory vessel became an everyday machineConnect Dewar's cryogenic vessel to the modern thermos and identify how use and damage affect performance.A laboratory solution became household technology because the same physics works for hot and cold contents.

Questions this course answers

What does the vacuum mainly remove from the space between a thermos's walls?

With very few molecules between the walls, air cannot circulate and cannot carry much heat by molecular collisions.

Why does a thermos use a reflective inner surface?

A reflective surface absorbs and emits less thermal radiation, so it reduces the remaining radiative exchange.

Why does opening the lid repeatedly shorten a thermos's hot time?

The lid blocks moving air and evaporation; opening it repeatedly reintroduces those heat-loss routes.

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