Why convection occurs

Convection affects everything from the heating of your house, to the process of heat transfer within the sun. In a gas, this is expressed not as a "vibration" but as an increased velocity for the particles, and therefore an increased pressure on the gas's container. For this reason, most materials expand as they are heated up.

This happens to the greatest extent in gases, but to a lesser extent in liquids and solids as well. When something expands, it becomes less dense; there are fewer particles, and therefore less mass, per unit volume than there were before. But in liquids and gases fluids , a region of lower density will rise and float above the higher density regions due to the influence of gravity. These two concepts, that heat causes a decrease in density and that fluids rise and fall according to density, combine to create the heat-transfer phenomenon of convection.

Convection is a method of thermal energy transfer where the transfer of heat occurs via fluid motion. This fluid motion is caused by the difference in density between hotter regions of the fluid and cooler regions.

These motions are called convection currents , and the convective movement of fluid continues as long as there is a temperature difference between regions.

This temperature difference is especially stark when there is a source of heat on one side of the fluid, such as a heater near the floor of a room. The warm air at the bottom continuously moves upward, while the cooler air moves downward to be heated and then subsequently also moves upward. The movement of air causes circular currents that will continue unless the air reaches an equilibrium temperature; a glass of water at room temperature will generally not have convective currents, while a glass of water with ice in it will have convective currents.

Convection is often described as a combination of two physical processes: advection and diffusion. Advection is the transport of matter by bulk motion, such as the movement of riverbed silt by the flow of the river. Diffusion is the transport of matter by particle motion from an area of high concentration to an area of low concentration, such as the movement of dye particles spreading through a glass of water.

As convection moves hotter matter higher and cooler matter lower, it does so both by moving the matter in bulk advection and in a particulate way diffusion.

Convection cannot, by definition, occur in solids because of the inability to create fluid flow in solid matter the particles cannot move relative to each other, but can only vibrate in place. Heat transfer in solids occurs instead by conduction, or the transfer of vibrational energy from one atom or molecule in a solid crystal to its neighbors.

There are some exceptions to this in soft solids where the particles can move past each other. This is because the particles in liquids and gases move faster when they are heated than they do when they are cold.

As a result, the particles take up more volume. This is because the gap between particles widens, while the particles themselves stay the same size. The liquid or gas in hot areas is less dense than the liquid or gas in cold areas, so it rises into the cold areas.

The denser cold liquid or gas falls into the warm areas. In this way, convection currents that transfer heat from place to place are set up. Convection currents can be seen in lava lamps. While less commonly observed than everyday examples of convection that happen at home and weather phenomena, there are a number of other examples of convection associated with air movement. A number of natural phenomena are related to convection related to geology.

A star has a convection zone where energy is moved by convection. Outside the core is a radiation zone where plasma moves. A convection current forms when the plasma rises and the cooled plasma descends. These different examples of convection show how convection occurs throughout many human-made and natural occurrences.

Now that you are familiar with examples of convection, consider expanding your knowledge of related scientific phenomena. Start by exploring ten condensation examples common in real life. All rights reserved. What Is Convection? Everyday Examples of Convection There are numerous examples of convection in everyday life, including several common household occurrences.

This hot water rises and cooler water moves down to replace it, causing a circular motion. As a result, the ice melts from a solid to liquid. This is because the action of the running water transfers heat into the food faster than if the frozen item was placed in still water.