# Definition of temperature and thermal equilibrium

Definition of temperature

Ever touched ice? What do you feel when your hands touch ice? What if what you touch is fire? When touching ice, your hands feel cold, when you touch the fire, your hands feel hot. Hot, warm, cool, cold states what?

The concept of temperature starts from the heat and cold experienced by our sense of touch. Based on what is felt by the sense of touch, we say an object is hotter than another object or an object is cooler than another. Hot objects have higher temperatures while cold objects have lower temperatures. The cooler an object, the lower the temperature. Conversely, the hotter an object, the higher the temperature. The size of the heat or cold of an object is called temperature. In the subject of gas kinetic theory, you will understand more deeply the definition of temperature; what happens to the molecules form an object so that it can feel hot, warm, cool or cold.

Size of heat or cold is an object that is only based on touch, or sense of touch humans are not very clear. Everyone can feel the heat or cold of an object at different levels. A baby can feel in pain when touching water that is not too hot for adults. Likewise, despite contacting the same object, the heat felt by different parts of the body may not be the same. Therefore we need a device that can be used to measure temperature with certainty and can be trusted by everyone.

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Thermal equilibrium

When high-temperature objects in contact with low-temperature objects, some heat from objects with high temperature move to a low-temperature object until both objects have the same temperature. When hot water in contact with ice, some heat from the hot water moves to ice. Heat transfer stops after the mixture of hot and ice reaches the same temperature. When the combination of hot water and ice reaches the same temperature, the mix of hot water and ice is in thermal equilibrium. Likewise, when boiling water in contact with cold water, some of the heat moves from hot water to cold water.

Heat transfer stops after a mixture of hot water, and cold water turns into warm water. When all the water becomes to warm, all water has reached the same temperature. When the hot and cold water mixture reaches the same temperature, the mix of hot and cold water is in thermal equilibrium.

If two or more than two objects that have different temperatures touch each other until they reach the same temperature, objects that have reached the same temperature are said to be in thermal equilibrium.

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