Heat Transfer
Heat and temperature are closely related concepts. While temperature describes how cold or hot a body is, heat is defined as the energy that is transferred from one body to another due to temperature differences. Temperature is measured using thermometer. Common units of temperature are degrees Celsius (°C), degrees Fahrenheit (°F), and the standard unit Kelvin (K). Heat is expressed in terms of the unit calorie (cal.).
When two or more objects with different temperatures are in contact with each other, heat transfers spontaneously from the object with the higher temperature to the object with lower temperature. The transfer of heat stops only when the objects in contact already have the same temperature, or are said to be in thermal equilibrium.
Why does a metal doorknob feel cold to the touch early in the morning? This is because metals are good conductors of heat. When you hold a metal, you transfer heat from your hand, making it seem colder than nonmetals in the same area.
Heat can be transferred from a body to another by three modes: conduction, convection, and radiation.
