Heat is a form of energy that is transferred from hotter objects to colder objects. It causes particles in objects to move faster and take up more space, resulting in expansion. Heat comes from sources like the sun, fire, and friction between objects. It is transferred through conduction, with hotter bodies losing heat energy to cooler bodies. Temperature measures the thermal energy or heat of an object, with higher temperatures indicating more heat energy. Thermometers use the expansion of liquids like mercury or alcohol to measure temperature on scales like Celsius and Fahrenheit. Materials that conduct heat well are called thermal conductors while thermal insulators conduct heat poorly.