Unit 13: Thermal Energy and Heat Transfer
The difference between how hot something is and how much thermal energy it holds, and the three ways heat actually moves from one place to another.
7 topics · 22 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Temperature versus Thermal Energy
- How it worksHow does temperature measure the average motion of particles while thermal energy adds up all of it?
- Common mistakeWhy isn't temperature just a measure of the total heat energy an object contains?
- Ties togetherHow does the split between temperature and thermal energy explain why specific heat capacity needs its own number for every material?
Your turn1 of 2
A small cup of hot tea and an enormous swimming pool full of lukewarm water can both register the exact same temperature on a thermometer, yet the swimming pool clearly holds vastly more total energy than the small cup ever could. Why can a cup of tea and a swimming pool be the same temperature while holding wildly different amounts of energy?Heat Transfer by Conduction
- How it worksHow does conduction pass thermal energy from particle to particle without the particles themselves traveling anywhere?
- Common mistakeWhy isn't cold something that actually flows into your hand when you touch an ice cube?
- Common mistakeWhy doesn't a metal railing outside on a cold morning actually sit at a lower temperature than a wooden fence right beside it?
- Going furtherWhat happens to the rate of conduction when a metal rod is replaced with one made of a better insulator?
Your turn1 of 2
A metal spoon left resting in a pot of hot soup quickly becomes too hot to touch comfortably, while a wooden spoon resting in that exact same pot of soup stays comfortably cool to the touch the entire time. Why does a metal spoon left in hot soup feel scalding while a wooden spoon in the same soup stays cool?Heat Transfer by Convection
- How it worksHow does heated fluid rise and cooler fluid sink to set up a continuous convection current?
- Common mistakeWhy doesn't convection happen the same way in a solid as it does in a liquid or gas?
- Ties togetherHow does convection move heat by actually carrying matter along, unlike the particle-to-particle handoff of conduction?
Your turn1 of 2
Turning on a space heater near the floor of a room eventually warms the whole room, but the air right up near the ceiling often ends up noticeably warmer than the air still near the floor where the heater itself sits. Why does warm air from a heater end up gathering near the ceiling instead of staying near the floor?Heat Transfer by Radiation
- How it worksHow does thermal radiation carry energy as electromagnetic waves that need no medium to travel through?
- Common mistakeWhy doesn't radiant heat require any particles at all to travel from a hot object to you?
- Ties togetherHow does radiation carry energy through the vacuum of space where conduction and convection have no matter to work through?
Your turn1 of 2
Standing outside on a sunny day, you can feel real, measurable warmth on your skin coming from the Sun, despite the Sun sitting about 150 million kilometers away across the near-total emptiness of outer space, with no air or any other matter filling most of that vast distance. Why can you feel the Sun's warmth on your skin across 150 million kilometers of empty space?Specific Heat Capacity
- How it worksHow does specific heat capacity decide how much a given amount of energy raises an object's temperature?
- Worked exampleFind the heat needed to raise the temperature of 2 kg of water by 15 degrees C, given water's specific heat of 4186 J per kg per degree C.
- Common mistakeWhy doesn't every material heat up by the same amount when given the same amount of energy?
Your turn1 of 2
Find the heat needed to raise the temperature of 34.88 kg of water by 52 degrees C, given water's specific heat of 4186 J per kg per degree C.Phase Changes and Latent Heat
- How it worksHow does latent heat go into breaking apart molecular bonds instead of raising the temperature during a phase change?
- Worked exampleFind the heat needed to melt 0.5 kg of ice, given the latent heat of fusion of water is 334000 J per kg.
- Common mistakeWhy doesn't the temperature of boiling water keep climbing past 100 degrees C no matter how high the flame is turned?
Your turn1 of 2
Find the heat needed to melt 13.94 kg of ice, given the latent heat of fusion of water is 334000 J per kg.Thermal Expansion
- How it worksHow does heating a material make its particles vibrate through more space and push the whole object to expand?
- Common mistakeWhy doesn't every material expand by the same amount for the same rise in temperature?
- Worked exampleFind how much a 10 meter steel beam with an expansion coefficient of 0.000012 per degree C lengthens when heated by 40 degrees C.
Your turn1 of 2
Find how much a 70 meter steel beam with an expansion coefficient of 0.000012 per degree C lengthens when heated by 39 degrees C.