Whats so special about convection conduction and radiation

What’s so special about convection, conduction, and radiation?

Before we can start, we need to be sure we understand what “transfer” means.

n Convection n Conduction n Radiation – Are ALL ways of transferring heat n Heat always flows away from a hot material toward a cold material

One picture is worth…. .

n In a solid material, every atom is bonded to a neighboring atom. n If we apply heat to one part of a solid, like the bottom of a metal pan, the atoms begin to vibrate.

Conduction As the heated atoms begin to vibrate more, the bonds between the atoms also begin to vibrate, causing neighboring atoms to collide. n This passes the vibrations, or heat, from one atom to the next. n Eventually, the energy spreads throughout the all the molecules of the solid, and the temperature increases. n

So, (in words) what is conduction? n the direct transfer or movement of warmth and energy from one molecule to another molecule by collision. n What happens when you place a metal pot or pan on a hot stove? n Does the whole pan get hot, or only the part touching the heat? n. Most solid metal materials transfer heat by conduction.

Conduction n This is why when a metal pot or pan is placed on a hot stove, the whole pan becomes hot, rather than only the bottom.

What are some other examples n Of conduction? ? ? Roasting marshmallows …… Metal shed in sun…… Walking on sand ……

Convection n The Earth is heated by radiation from the sun (transporting energy via electromagnetic waves). n Heating of earth's surface and atmosphere by the sun drives convection within the atmosphere and oceans, which produces winds and ocean currents.

n Convection is the transfer of heat by the actual movement of warmed matter. What’s happening here? Convection is typically demonstrated in liquids and gases and usually arises from differences in temperature and density.

Where is the cooler water? Where is the warmer water? Examples of convection can be seen in the Earth’s atmosphere and in the ocean currents.

Convection Currents Air over the land is warm, cool air over water (ocean) rushes in and pushes the warm air up – this is what causes the wind to blow (convection currents)

Another way to see the same thing…. n In the atmosphere, as air warms it rises, it allows cooler air to flow in underneath. n This, along with the turning of the Earth, creates winds.

What causes Convection currents to circulate? n Lighter (less dense), warm material rises while heavier (more dense) cooler material sinks. n This movement creates circulation patterns known as convection currents in the atmosphere, in water, and in the mantle of Earth.

Convection Currents n This continual rising and falling or air causes breezes, winds, tornados, and thunderstorms, ocean currents, and also causes the geologic plates of the earth to move.

Convection in the lava lamp means that we also need to talk briefly about density…. . what is density? Are cooler materials more or less dense than warm materials?

Can we pour air? Is air a fluid? Can we pour air?

Convection in the aquarium……… Heat causes warm water and molecules to move faster and faster as they expand. The cool water around the warm water squeezes the warm water up.