How does heat move?
Heat only ever moves three ways: by touch, carried by moving air or water, or as invisible infrared light. Race copper against wood, cool a pot with a fan, feel a hot tawa's glow, watch a spoon in chai, keep a geyser hot overnight, and find out why metal only feels colder.
▶ Play with it · Read the 60-second explainer · Watch the 40-second video
- Three ways, and only three. Heat moves from hot to cold by conduction (atom to atom through a solid), convection (carried by moving air or water) or radiation (infrared light, which even crosses a vacuum). Each has its own law: q = k A ΔT ÷ d, q = h A ΔT and q = ε σ A (T⁴ − Tₛ⁴).
- Materials decide conduction. Copper conducts heat about 2,700 times better than wood. That's why a silver spoon in chai can burn your fingers while a steel one stays cool, and why a wooden handle is safe to hold.
- Moving fluid carries heat faster. Still air clings to a surface as a warm blanket. A fan or an air fryer strips it away, raising h four or five times; oil and water do better still.
- Insulation only slows heat. Foam is mostly trapped gas, a terrible conductor. Layers add their resistances, so doubling a fridge's foam roughly halves its heat leak. Fins do the opposite: they add area to shed heat faster.
- Surprises: latent heat, flasks and cold metal. Melting and boiling soak up heat without warming. A vacuum flask blocks all three routes. And metal isn't colder than wood in the same room: it pulls heat from your hand faster, so it feels colder.
| Term | Meaning |
|---|---|
| Conduction | Heat passed from atom to atom through touch. Fourier's law: q = k A ΔT ÷ d. |
| Thermal conductivity (k) | How well a material conducts heat, in W/m·K: copper 400, steel 16, wood 0.15, still air 0.026. |
| Convection | Heat carried by a moving fluid: natural when warm fluid rises by itself, forced when a fan or pump drives it. q = h A ΔT. |
| Radiation | Heat carried by light, mostly infrared. It crosses empty space and grows as the fourth power of temperature in kelvin. |
| Emissivity (ε) | How well a surface radiates compared with a perfect black body: about 0.9 for black iron, 0.03 for silvered glass. |
| Thermal resistance (R) | How hard a layer makes it for heat to pass: R = d ÷ k. Layers in a row add up. |
| Latent heat | Heat that melts or boils something without changing its temperature: 334 J/g for ice, 2,257 J/g for water. |
| Thermal effusivity | How strongly a material pulls heat from something touching it, √(kρc). It's why metal feels colder than wood. |
From desert ice houses and clay water pots to vacuum flasks and the glowing math of Planck: how people learned the three ways heat moves.
- 1798 · Boring cannons makes endless heat (Count Rumford (Benjamin Thompson), Munich, Bavaria)
- 1800 · Hidden heat beyond the red (William Herschel, Slough, England)
- 1822 · The mathematics of heat (Joseph Fourier, Paris, France)
- 1856 · Carbon dioxide warms in the sun (Eunice Newton Foote, Albany, New York)
- 1879 · Twice as hot, sixteen times the glow (Josef Stefan and Ludwig Boltzmann, Vienna, Austria-Hungary)
- 1892 · A bottle with nothing in its walls (James Dewar, Royal Institution, London)
- 1900 · Glowing heat comes in packets (Max Planck, Berlin, Germany)
The full story, with 20 moments, charts, people and 30 sources: glassbox.how/e/heatclear/history. The data lives in history.json.
Made with the Glassbox studio from this box's storyboard (window.glassbox.director). Free to reuse under CC BY 4.0.
| File | What | Size |
|---|---|---|
glassbox/reel.mp4 |
Reel / Short, with captions and soundtrack | 1080×1920 |
glassbox/video.mp4 |
YouTube video, with captions and soundtrack | 1920×1080 |
glassbox/slide-1…10.jpg |
Instagram carousel | 1080×1350 |
glassbox/thumb.jpg |
YouTube thumbnail | 1280×720 |
glassbox/cover.jpg |
Share card and repo social preview | 1200×630 |
glassbox/history-reel.mp4 |
“History in 10 moments” Reel / Short | 1080×1920 |
glassbox/history-slide-*.jpg |
History carousel | 1080×1350 |
glassbox/post.json |
Post copy and schedule used by the publish kit |
This box has no accounts and no ads, and it ships its own fonts and libraries. When you run it yourself it sends nothing anywhere. On glassbox.how, the site's /bar.js also loads Glassbox's analytics: Google Analytics to count visits (it asks first in the EU, UK and Switzerland, and stays off when your browser sends Global Privacy Control or Do Not Track) and ClickTrust to detect bots.
It remembers a few things in your own browser only, and never sends them anywhere:
| Browser storage key | What it holds |
|---|---|
heatclear.v1 |
Which chapters you have opened, your best quiz scores, and sound on or off. |
Exactly what each one sees is at glassbox.how/privacy.
- Code: MIT. Use it, change it, ship it.
- Explanations, text, images and videos (
glassbox.json,glassbox/): CC BY 4.0. Credit “Glassbox, glassbox.how/e/heatclear”. - Third-party parts keep their own licences: three.js (MIT), Geist, Instrument Serif (SIL OFL 1.1).
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python3 -m http.server 8000Three.js and the fonts ship in vendor/ and fonts/, so it also works offline.
Then open http://localhost:8000.
| File | What |
|---|---|
index.html, css/app.css |
The page and its styles |
js/app.js, js/stage.js, js/ui.js, js/kit.js |
The shared Glassbox 3D engine: chapters, 3D stage, controls, quiz, video director |
js/chapters/*.js |
One file per chapter: the 3D model, controls, text, key terms, quiz and video scenes |
js/heat.js |
Heat-transfer physics (conductivities, Fourier, Newton's cooling and Stefan–Boltzmann helpers, convection correlations, vapour pressure), chart boards, heat puffs and a hand, shared by the chapters |
glassbox.json |
Title, question, explainer beats, key terms, browser storage and credits shown on glassbox.how |
reel in each chapter |
The storyboard the Glassbox studio records into short videos |
glassbox/ |
The published video, slides, thumbnail and post copy |
fonts/, vendor/three/ |
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