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Temperature measures the hotness or coldness of a body and is recorded with a thermometer. Heat is the movement of energy from one material to another due to a temperature difference. Temperature is proportional to average translational kinetic energy, while heat represents the actual energy transfer between objects.

When hot and cold water mix, heat transfers from the hotter water to the colder water until their temperatures equalize. This energy movement continues until thermal equilibrium is reached, at which point no further heat transfer occurs between the two bodies.

Thermal equilibrium is the condition when there is no further heat transfer between two connected systems because they have reached the same temperature. Once two bodies attain uniform temperature, the heat transfer stops completely, and the system remains in equilibrium.

Insulators like vacuum delay the process of reaching thermal equilibrium by restricting heat transfer between systems. A thermal flask keeps coffee hot for extended periods because the vacuum between its walls acts as an insulator, slowing energy loss to the surroundings.

Temperature is operationally defined as the quantity measured with a thermometer, making it the standard tool for recording hotness or coldness. Thermometers respond to temperature differences and reach thermal equilibrium with the object being measured, providing accurate readings of temperature.

A warm object will cool down when placed in a colder environment until it reaches the temperature of that environment. Heat transfers from the warmer object to the cooler surroundings, and this process continues until thermal equilibrium is established between the object and its environment.

Differences in temperature maintain the transfer of heat throughout the universe, affecting everything from atomic and molecular behavior to weather patterns and stellar life cycles. Heat always flows from regions of higher temperature to regions of lower temperature, driven by these temperature gradients.