Temperature is the degree of hotness or coldness of an object. When we talk about something feeling hot (like the soup we drink when were sick) or cold (like the snow, especially if youre not wearing gloves), were talking about temperature.

The temperature of an object, usually measured in degrees-Fahrenheit or degrees-Celsius, tells us how much heat, or energy, the object has. A boiling cup of water has very active molecules moving around very quickly and producing the heat we feel on our hands and faces. Colder objects don't have as much energy. Their molecules are much less active.

Think about this: If you put an oven mitt on a hot dish fresh from the stove, the oven mitt usually picks up some of the heat, right? This is one of the main ideas of thermodynamics, which studies (partly) how energy and heat work hand-in-hand. If there isn't any heat being transferred between two objects, those objects are the same temperature. But if one object is hotter, heat will flow naturally from the hotter object to the colder object; this is why the oven mitt gets warm.

Scientists usually use water to compare temperatures of things because its pretty easy to remember the boiling point and freezing point of good-old H₂O: Water boils at 100 degrees Celsius and freezes at zero degrees Celsius. Its a little harder to remember the Fahrenheit scale, but water boils at 212 degrees Fahrenheit and freezes at 32 degrees Fahrenheit.

The Celsius scale is used in most of the world, except for Belize, Myanmar, Liberia and the United States. Scientists use the Kelvin scale, which doesnt measure temperature in degrees. Zero Kelvin is also called absolute zero, the coldest temperature and lowest energy level. Absolute zero is equal to about minus-273 degrees Celsius.