# Heat Transfer & Thermodynamics Explainer By The unique one Topic: Physics & Chemistry [Open the interactive Jig](https://ask.jig.com/j/2MrSkcvcGoVr) ## Guide ### 1. Follow the heat Heat always flows from warmer things to cooler things\. On this bench we follow it three ways: up into a winter night sky, through the walls of an ice box, and into a gas being warmed\. Drag empty space to turn the bench\. Use the arrows below to move between steps\. ### 2. A clear winter night The snowy ground and the person both give off infrared, an invisible kind of light that carries heat\. With a clear sky, almost all of it escapes straight out to space\. So the ground and the person cool quickly, and frost can form\. Orange streaks show infrared heat leaving the ground and the person\. ### 3. Clouds work like a blanket Clouds are made of water droplets that soak up infrared\. They send part of it back down to the ground and to you, so you lose heat more slowly\. Clouds do not make heat; they slow its escape, so a cloudy night feels warmer\. Pink streaks are heat the clouds send back\. Switch the clouds off and on to compare\. ### 4. An ice box with two layers This box has wooden walls 2\.0 cm thick, lined inside with felt 1\.0 cm thick\. Heat gets in through 1\.1 square metres of wall\. The room is 15 °C and the ice stays at 0 °C while it melts\. The question gives no conductivities, so we use typical ones\. Conductivity says how easily heat passes through a material: 0\.12 watts per metre per degree for pine, and 0\.07 for felt\. ### 5. Heat squeezes through the walls Heat leaks in through the wood and then the felt, one after the other\. Each layer slows it, and their slowing effects simply add up\. The glowing line shows the temperature falling from 15 °C to about 7 °C inside the wood, then to 0 °C across the thin felt\. Heat flow equals area times temperature difference, divided by the sum of each layer's thickness over its conductivity\. That is 1\.1 times 15, divided by 0\.31: about 53 watts\. ### 6. How much ice melts in an hour? About 53 joules of heat leak in every second\. A joule is a small amount of energy, so that is 192,000 joules in an hour\. Melting 1 kg of ice needs 334,000 joules\. So about 0\.57 kg of ice melts each hour, roughly a bag of sugar\. Mass melted equals 53\.3 watts times 3,600 seconds, divided by 334,000 joules per kilogram: about 0\.57 kg every hour\. ### 7. Nitrogen held at constant volume Here 3 kg of nitrogen is heated from 10 °C to 100 °C, a rise of 90 degrees\. The pins stop the piston moving, so the gas does no work\. All 200\.6 kJ of heat goes into internal energy: the molecules simply move faster\. Heat equals 3 kg times 743 joules per kilogram per degree, times 90 degrees: 200\.6 kJ\. Work is zero, so internal energy rises by 200\.6 kJ\. ### 8. Nitrogen at constant pressure Now the piston is free and carries a weight, so the pressure stays the same\. The warming gas expands and lifts it, doing 80\.2 kJ of work\. The same 90 degree rise still needs 200\.6 kJ of internal energy, so 280\.8 kJ of heat is needed in all\. Heat equals 3 times 1,040 times 90: 280\.8 kJ\. Work equals heat minus internal energy: 80\.2 kJ\. Orange is heat in, purple is internal energy, green is work\. ### 9. Same warming, different bills Both gases warm by the same 90 degrees, so their internal energy grows by the same 200\.6 kJ\. The free piston needs extra heat because some energy leaves as work\. Heat in always equals internal energy gained plus work done\. This is the first law of thermodynamics: energy is never lost, only moved or changed\.