Heat vs. temperature
Heat and temperature are interconnected concepts often confused in everyday discussions. Temperature measures the average kinetic energy of atoms in a substance, reflecting their motion, and is quantified using various scales, most commonly Fahrenheit and Celsius. The Fahrenheit scale defines the freezing and boiling points of water as 32°F and 212°F, respectively, while in the Celsius scale, these points are 0°C and 100°C. Heat, on the other hand, is energy transferred between objects due to a temperature difference, occurring through conduction, convection, or radiation. For instance, on a winter day, heat transfers from warm indoor air through a window pane to the colder outside air. This process is fundamental to various applications, including climate science. The increase in heat transfer to Earth’s oceans and atmosphere, primarily from industrial processes, contributes to climate change and global warming, illustrating the significant role of heat in environmental shifts. Understanding the distinction between heat and temperature is crucial for grasping their implications in both scientific contexts and everyday life.
Subject Terms
Heat vs. temperature
Definition
The concepts of heat and temperature are closely related, so these quantities are often confused, and the terms are sometimes used interchangeably (but incorrectly) by laypersons. Temperature is a measurement of the average kinetic energy—that is, physical motion—of the atoms in a substance. The kinetic energy of an object is calculated according to the following formula:
EK = 1/2MV2
where EK is kinetic energy, M is mass, and V is velocity. The kinetic energy of atoms is generally due to a combination of their directional velocity and vibrational motion. This energy may be measured by a thermometer.
The two most common temperature scales in use are the Fahrenheit and Celsius (formerly centigrade) scales. In the Fahrenheit scale, the freezing point of water is defined as 32° and the boiling point is defined as 212°. In the Celsius scale, the freezing point of water is defined as 0° and the boiling point is defined as 100°. In science and engineering, the Rankine and Kelvin temperature scales are used. These are called absolute temperature scales, because their zero reference level is absolute zero, the lowest temperature that can theoretically exist. At absolute zero, the total kinetic energy of all the atoms in a substance is zero.
Heat is the form of energy transferred across the boundary of an object as a result of a temperature difference across that boundary. Consider what happens across a pane of window glass on a cold winter day. The air inside the heated house is warmer than the air outside. This temperature difference across the window pane causes an energy flow through the glass from the warm air inside to the cold air outside: The outer air next to the glass is warmed, while the air inside the house cools, requiring a heating system to maintain a constant, comfortable temperature. There are three types of heat transfer: conduction, convection, and radiation. All result from a temperature difference between an object and its surroundings.
Conduction is the primary mechanism of heat transfer in solids. It occurs because of molecular activity in the solid. Convection is the primary mechanism of heat transfer through fluids and results from bulk mixing between fluid layers. Radiation, the third type of heat transfer, is the only mechanism that can transfer heat through a vacuum. When the Sun heats the Earth, there is no solid between them through which heat can be conducted, nor is there is any fluid through which heat can be convected. The temperature difference between the Sun and the Earth still causes heat transfer to the Earth by means of electromagnetic waves. Electromagnetic waves can also transfer energy in the form of light, X-rays, or radio waves.
Heat is measured as a function of the temperature change of a substance when heat transfer occurs. The commonly used units for heat are the calorie, the joule, and the British Thermal Unit (BTU). A calorie is the amount of heat required to raise the temperature of one gram of water by one degree Celsius. A BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. One joule is equal to 0.239 calorie.
Significance for Climate Change
Heat transfer to the Earth’s oceans and atmosphere is the first step in, and at the very heart of, climate change. Most of the industrial or mechanical processes in which humans engage release heat as a waste by-product. For example, all fossil fuel and nuclear power plants generate waste heat as a by-product of producing power. A typical power plant may have an efficiency of between 35 percent and 50 percent, meaning that this percentage of the stored energy in a fuel is converted to useful energy, while the remaining energy is discharged to the atmosphere or some body of water as waste heat. This heat transfer to the environment causes a temperature increase of the environment. This temperature increase is a contributor to global warming. Even a degree or two increase in the average temperature of the oceans or the atmosphere can cause profound effects upon Earth’s biosphere. All combustion engines also dissipate waste heat to the environment, as do heating and cooking appliances. Only power produced by wind, water, or does not directly contribute to global warming, although these types of power production can have other effects.
Bibliography
Cengel, Yunus A., and Michael Boles. Thermodynamics: An Engineering Approach. 5th ed. New York: McGraw-Hill, 2006.
"Difference Between Heat and Temperature." Dabedan, 23 Apr. 2024, www.dabedan.com/en/understanding-the-difference-between-heat-and-temperature/. Accessed 19 Dec. 2024.
"Heat vs. Temperature." Energy Education, energyeducation.ca/encyclopedia/Heat‗vs‗temperature. Accessed 19 Dec. 2024.
Holman, Jack P. Heat Transfer. 9th ed. New York: McGraw-Hill, 2002.
Thurman, Harold V., and Elizabeth Burton. Introductory Oceanography. 9th ed. Upper Saddle River, N.J.: Prentice Hall, 2001.