For an explanation, see the main splats page
The principles of heat
- All matter has a capacity to hold heat, measured as its specific heat or heat capacity. Heat capacity and temperature are not the same thing at all.
- Heat makes changes happen, including expansion and contraction. The varying expansion coefficients of materials can be measured and used in many ways.
- Heat generally increases the chemical rate of reaction, and it can also cause pyrolysis, the breakdown of compounds under the application of heat.
- Heat at the junction of two metals causes a potential difference. The thermocouple formed can be used to generate electricity or to measure temperature.
- Heat is a form of energy and travels mainly as infrared radiation, but also by convection and conduction. Heat may be converted to other forms of energy.
- In 1849, William Thomson ( Lord Kelvin ) coined the term 'thermodynamics' to describe the science of heat flow which is basic to the scientific study of energy.
- The movement of heat happens in accordance with the laws of thermodynamics, especially the second law, which means heat goes from warmer to cooler areas.
- Sufficient heat will make a change of state happen: boiling, condensing, melting, solidifying (freezing), sublimation, to form gases, liquids and solids.
- The rate at which bodies cool follows Newton's law of cooling. As the difference between an object and its environment gets less, the rate of cooling slows.
- When matter is heated, energy is gained and the molecules move or vibrate faster. As matter cools, the molecules lose energy and move or vibrate more slowly.
- Heat generally travels from hot to cold. Convection occurs in gases and liquids. Conduction occurs in solids, liquids and gases. Radiation can occur in a vacuum
- Isaac Newton showed that the rate of cooling in a hot body was proportional to the difference between it and its surroundings: that hot things cool faster.
- Metals are usually good conductors of heat, non-metals are usually poor conductors. Conduction is the transfer of energy from one atom or molecule to the next.
- A higher temperature means more energy has been stored in a body than when it was a lower temperature. Temperature can be measured with a thermometer.
- Refrigeration depends on adiabatic cooling to move heat from one place to another, pumping it out of the cold compartment. Cold is an absence of heat.
- There is a lowest possible temperature, called absolute zero. Matter which is at absolute zero on the Kelvin scale is completely motionless in all dimensions.
- In 1761 Joseph Black discovered that ice absorbs heat without changing temperature when melting, and outlined the effects of latent and specific heats.
- Latent heat is absorbed or released during a change of state. This is why steam at 100º C contains more heat than an equal mass of water at 100º C.
- In 1798, Count Rumford reported that mechanical energy could be converted to heat when cannon barrels were bored with drills, whether they were blunt or sharp.
- By careful measurement, Count Rumford was able to establish that if heat had any mass, then a single calorie had to be less than 0.000013 milligrams.
- William Herschel used a thermometer to detect heat falling outside the visible solar spectrum, and so became the first to observe infrared radiation.
- We cannot see infrared radiation, although we can detect it as heat, and we can also detect it with some photographic films and special cameras.
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