Temperature is how hot or cold something is. The best-known temperature scales are Celsius and Fahrenheit.
The Celsius (C) scale is part of the metric system of measurements and is used everywhere except in the USA. It is named after Swedish astronomer Anders Celsius, who developed it in 1742.
Celsius is also known as centigrade because water boils at 100°C. Cent is the Latin prefix for 100. Water freezes at 0°C.
On the Fahrenheit (F) scale water boils at 212°E It freezes at 32°F.
To convert Celsius to Fahrenheit, divide by 5, multiply by 9 and add 32.
To convert Fahrenheit to Celsius, subtract 32, divide by 9 and multiply by 5.
The Kelvin (K) scale used by scientists is like the Celsius scale, but it begins at –273.15°C. So 0°C is 273.15K.
Cold: absolute zero is –273.15°C. The coldest temperature ever obtained in a laboratory is –272.99999°C. Helium turns liquid at –269°C. Oxygen turns liquid at –183°C. Gasoline freezes at –150°C. The lowest air temperature ever recorded on Earth is –89.2°C.
Hot: the highest shade temperature recorded on Earth is 58°C. A log fire burns at around 800°C. Molten magma is about 1200°C. Tungsten melts at 34 1 0°C. The surface of the Sun is around 6000°C. The center of the Earth is over 7000°C. A lightning flash reaches 30,000°C. The center of a hydrogen bomb reaches four million °C.
The blood temperature of the human body is normally 37°C. A skin temperature above 40°C is very hot, and below 31°C is very cold. Hands feel cold below 20°C and go numb below 12°C. Anything above 45°C that touches your skin hurts, although people have walked on hot coals at 800°C. The knee can tolerate 47°C for 30 seconds
The inside of your body stays at a constant temperature of 37°C (98°F), rising a few degrees only when you are ill.
Your body creates heat by burning food in its cells, especially the ‘energy sugar’ glucose.
Even when you are resting, your body generates so much heat that you are comfortable only when the air is slightly cooler than you are.
When you are working hard, your muscles can generate as much heat as a 2 kW heater (a typical room heater).
Your body loses heat when you breathe in cool air and breathe out warm air. Your body also loses heat by giving it off from your skin.
The body’s temperature control is the tiny hypothalamus in the lower front of the brain.
Temperature sensors in the skin, in the body’s core, and in the blood by the hypothalamus tell the hypothalamus how hot or cold your body is.
A very hot day can sometimes make us feel uncomfortable. Splashing ourselves with cool water is often welcome relief!
If it is too hot, the hypothalamus sends signals to your skin telling it to sweat more. Signals also tell blood vessels in the skin to widen — this increases the blood flow, increasing the heat loss from your blood.
If it is too cold, the hypothalamus sends signals to the skin to cut back skin blood flow, as well as signals to tell the muscles to generate heat by shivering.