Heat

THERMAL ENERGY

All matter is made of atoms; and those atoms are constantly in motion. Either vibrating in place such as in a solid material or flying around excitedly such as in a gas, the atoms that make up all substances have energy that causes them to move. Thermal energy refers to the total energy of the particles in an object. In other words, if you add up the energy of each individual particle in the object, you will have its thermal energy.

Temperature

Temperature is often confused with thermal energy. While thermal energy is the total energy of the particles in an object, temperature is a measurement of the average kinetic energy of the particles in a substance. In other words, when we measure the temperature of something, we are measuring how fast its particles are moving. Higher temperatures indicate that the particles are moving faster while lower temperatures indicate that the particles are moving slower. Objects with the same thermal energy do not necessarily have the same temperature. For example, a very small but hot object such as a match may have the same thermal energy as a very large but cold object such as an ice sculpture. Likewise, objects with the same temperature do not necessarily have the same thermal energy. Two cups with different amounts of room temperature water will have different thermal energy. The cup with more water has more particles, thus more total energy.

Temperature Scales

The metric unit of measure for temperature is degrees Celsius (°C). The Celsius scale was developed to coincide with the melting point and boiling point for water, a substance most people are very familiar with. 0°C is the temperature that water freezes, and 100°C is the temperature that water boils. In physics and chemistry, we often use another measurement for temperature, Kelvin (K). The Kelvin temperature scale is based on the Celsius scale, but it is shifted down so that 0 K coincides with absolute zero, the theoretical temperature at which there is no particle motion at all. A third common unit of temperature, Fahrenheit (°F), is non-metric and only used in some parts of the world (including the United States).

HEAT

Like temperature, many people often confuse the concept of heat with thermal energy. In science, heat refers to the transfer of thermal energy between substances. Heat always flows from warmer substances to cooler substances until they reach the same temperature, called the equilibrium temperature, as shown in the diagram below.

This is why we feel the sensation of “hot” or “cold” when we touch hot and cold objects. If you sit on a metal slide on a hot summer day, you may burn your legs. This is because the slide is warmer than your skin, so thermal energy flows from the slide into your legs, causing a “hot” sensation. Likewise, if you hold an ice cube in your hand, you will feel a “cold” sensation. This is because your hand is warmer than the ice cube, so thermal energy flows out of your hand into the ice cube. The energy leaving your hand causes you to sense “cold” and can be seen melting the ice cube. It is important to realize that “cold” is simply a sensation. There is no such thing as “cold” or “cold energy”. Things we refer to as cold simply have less thermal energy that what we perceive as a normal, or room temperature.

HOT 2 COLD SONG

Types of Heat

There are three types of heat: conduction, convection, and radiation.

Conduction transfers thermal energy by contact between particles. An example of conduction would be touching a hot stove or placing your hand in a bucket of ice water. Materials that transfer thermal energy easily or quickly are called thermal conductors. Metals, diamonds, and other dense substances tend to be good thermal conductors. Thermal insulators are materials that transfer thermal energy slowly or poorly. These types of substances include paper, wood, or cotton; materials that have a relatively low density.

Convection transfers thermal energy by the movement of currents in a fluid (a liquid or a gas). Convection currents form when a fluid is unevenly heated. Warmer fluid becomes less dense and rises to the top, while cooler fluid becomes denser and sinks toward the bottom. This creates a continuous current as the fluid heats and cools. An ocean breeze often forms in this way, with the warm air over the beach rising and the cool air over the water sinking and blowing on-shore.

Radiation transfers thermal energy through electromagnetic waves (light). Warming up by a campfire or keeping fast food warm under a heat lamp are both examples of radiation. We can also see radiation transferring thermal energy when Earth is warmed by sunlight. This example illustrates a unique aspect of radiation. Unlike conduction and convection, which both require matter to transfer thermal energy, radiation can transfer thermal energy through a vacuum such as space.

MISCONCEPTIONS ABOUT TEMPERATURE AND HEAT

CAN YOU "FEEL" TEMPERATURE?