Physics · Ch 10 — Thermal Properties of Matter
Temperature and Heat
Temperature and Heat
Temperature and Heat
Temperature is a relative measure — an indication of how hot or cold something is. A hot utensil has a high temperature; an ice cube has a low temperature. An object with a higher temperature than another is said to be hotter. Like "tall" and "short," "hot" and "cold" are relative terms.
We can perceive temperature by touch, but this sense is unreliable and its range is too limited for scientific work. A glass of ice-cold water left on a table on a hot summer day eventually warms up, while a cup of hot tea on the same table cools down. This tells us something fundamental: when the temperature of a body and its surroundings are different, heat transfer takes place between them. The transfer continues until the body and the surrounding medium reach the same temperature.
The direction of heat flow is always from the hotter object to the colder one. This is a natural tendency — heat never spontaneously flows from a cold body to a hot body.
The Distinction Between Temperature and Heat
Temperature and heat are related but distinct concepts. Temperature tells you how hot or cold something is — it is a measure of the average kinetic energy of the particles in a substance. Heat, on the other hand, is the energy that flows from one body to another because of a temperature difference.
Think of it this way: temperature is a state (a property of the body at a given moment), while heat is a process (energy in transit). A hot cup of tea has a high temperature; when it cools, heat flows out of it into the surrounding air. The tea's temperature drops, but the heat that left it is now in the air.
A common mistake is to say "an object contains heat." Objects contain internal energy, not heat. Heat is the energy transferred due to a temperature difference — it exists only during the transfer process.
Thermal Equilibrium
When two bodies at different temperatures are placed in contact, heat flows from the hotter to the colder one. Eventually, they reach the same temperature and no further net heat transfer occurs. At this point, the bodies are said to be in thermal equilibrium with each other. …