What’s so special about What’s so special about convection, conduction, convection, conduction,

and radiation?and radiation?

Before we can start, Before we can start,

we need to be sure we need to be sure

we understand what we understand what

““transfer” means.transfer” means.

ConvectionConvection Conduction Conduction RadiationRadiation

– Are Are ALLALL ways of transferring heat ways of transferring heat

Heat always flows away Heat always flows away fromfrom a hot material a hot material towardtoward a cold material a cold material

One picture is worth…..

In a solid material, In a solid material, every atom is every atom is bonded to a bonded to a neighboring atom. neighboring atom.

If we apply heat to If we apply heat to one part of a solid, one part of a solid, like the bottom of a like the bottom of a metal pan, the atoms metal pan, the atoms begin to vibrate. begin to vibrate.

ConductionConduction As the heated atoms As the heated atoms

begin to vibrate more, begin to vibrate more, the bonds between the the bonds between the atoms also begin to atoms also begin to vibrate, causing vibrate, causing neighboring atoms to neighboring atoms to collide.collide.

This passes the This passes the vibrations, or heat, vibrations, or heat, from one atom to the from one atom to the next.next.

Eventually, the energy Eventually, the energy spreads throughout the spreads throughout the all the molecules of the all the molecules of the solid, and the solid, and the temperature increases.temperature increases.

So, (in words) what is So, (in words) what is conduction?conduction?

the direct transfer or movement of the direct transfer or movement of warmth and energy from one molecule warmth and energy from one molecule to another molecule by collision. to another molecule by collision.

What happens when you place a metal What happens when you place a metal pot or pan on a hot stove? pot or pan on a hot stove?

Does the whole pan get hot, or only Does the whole pan get hot, or only the part touching the heat?the part touching the heat?

Most solid metal materials transfer heat by conduction.Most solid metal materials transfer heat by conduction.

ConductionConduction This is why This is why

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

What are some other What are some other examplesexamples

Of conduction?????Of conduction?????Roasting marshmallows ……

Metal shed in sun……

Walking on sand ……

ConvectionConvection

The Earth is heated by The Earth is heated by radiationradiation from from the sun the sun (transporting energy via electromagnetic waves).(transporting energy via electromagnetic waves).

Heating of earth's surface and Heating of earth's surface and atmosphere by the sun atmosphere by the sun drives drives convectionconvection within the atmosphere and within the atmosphere and oceans, which produces winds and oceans, which produces winds and ocean currents. ocean currents.

Convection Convection is the transfer of heat is the transfer of heat by the actual movement of warmed by the actual movement of warmed matter. matter.

Convection is typically demonstrated in liquids and gases and usually Convection is typically demonstrated in liquids and gases and usually arises from differences in temperature and density.arises from differences in temperature and density.

What’s happening here?

Examples of convection can be seen in the Earth’s Examples of convection can be seen in the Earth’s atmosphere and in the atmosphere and in the ocean currentsocean currents. .

Where is the cooler water?

Where is the warmer water?

Convection CurrentsConvection 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….

In the atmosphere, In the atmosphere, as air warms it as air warms it rises, it allows rises, it allows cooler air to flow in cooler air to flow in underneath.underneath.

This, along with the This, along with the turning of the turning of the Earth, creates Earth, creates winds. winds.

What causesWhat causes

Convection currents to circulate?Convection currents to circulate? Lighter (less dense), warm material Lighter (less dense), warm material

rises rises whilewhile heavier (more dense) heavier (more dense) cooler material sinks. cooler material sinks.

This movement creates circulation This movement creates circulation patterns known as convection patterns known as convection currents in the atmosphere, in water, currents in the atmosphere, in water, and in the mantle of Earth. and in the mantle of Earth.

Convection CurrentsConvection Currents

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

Convection Convection in the lava lamp in the lava lamp

Convection in the lava lamp means that we also need to talk briefly Convection in the lava lamp means that we also need to talk briefly about density…..what is density?about density…..what is density?

Are cooler materials more or less dense than warm materials? Are cooler materials more or less dense than warm materials?

Can we pour air?Can we pour air?

Is air a fluid?Is air a fluid?

Can we pour air?Can we pour air?

Convection in the aquarium………Convection in the aquarium………

Heat causes warm water and Heat causes warm water and molecules to move faster and faster molecules to move faster and faster as they expand. as they expand.

The cool water around the warm The cool water around the warm water squeezes the warm water up. water squeezes the warm water up.