Bell RingerName:3/2/2009

What’s do you believe happens when water changes from solid to liquid?

Response

Test Review

Hour 3 Hour 4 Hour 7

Phases of Matter

• Solid – has its own shape• Liquid – takes the shape of its container• Gas – completely fills its container

Phases of Matter

• Solid – has its own shape• Liquid – takes the shape of its container• Gas – completely fills its container

• Substances can change between phases– We’ve already seen water evaporation and

condensation in the cloud lab

Phase Changes

Gas – energy = Condensation

Liquid + energy = Evaporation

Evaporation

Evaporation - Is a phase change from liquid to gas and takes place at the surface of the liquid

Evaporation

Evaporation - Is a phase change from liquid to gas and takes place at the surface of the liquid

• But what is actually happening in terms of energy exchange?

Evaporation

Evaporation - Is a phase change from liquid to gas and takes place at the surface of the liquid

• Some molecules of liquid gain enough kinetic energy after being bumped by another molecule to escape into the space above the liquid

Evaporation

Evaporation - Is a phase change from liquid to gas and takes place at the surface of the liquid

• Some molecules of liquid gain enough kinetic energy after being bumped by another molecule to escape into the space above the liquid

– Just like the bowling balls– Some molecules are moving faster than

average and some are slower than average

Evaporation

• What does your skin when you step out of a hot shower into a cooler room?

Evaporation

• What does your skin when you step out of a hot shower into a cooler room?

– Cooling, and the droplets will eventually evaporate

Evaporation

• Practical examples:

– Dogs pant to cool themselves

– Wetting a canteen with cloth sides cools the water inside

Evaporation

• Name at least two ways to cool a cup of hot coffee.

Evaporation

• Name at least two ways to cool a cup of hot coffee.

– Blowing on it causes heat transfer by convection

– Pouring some into the saucer to increase surface area for evaporation

– Pouring it onto the saucer also causes heat transfer by conduction

– Putting a spoon into the cup causes heat transfer by conduction and then radiation

Sublimation

• Anyone every heard of a solid changing directly into a gas?

Condensation

Condensation -Is a phase change from gas to a liquid.

• Opposite of evaporation

• But what is actually happening in terms of energy exchange?

Condensation

• Occurs when the vapor molecules collide with slower moving molecules on a solid or liquid surface and lose kinetic energy

• Is a warming process, where the gas loses in the heat transfer and the solid or liquid that the molecule strikes gains in the heat transfer

Condensation

• Often both evaporation and condensation are occurring at the same time

Condensation in the Atmosphere

• Air contains water vapor

• Saturation – When air reaches the limit where it can’t hold any more water vapor

• Relative humidity - How much water is contained in the atmosphere

Clouds and Fog

• Convection causes expansion– Where warm air rises and expands

• Cooling occurs as the moist air expands– Water molecules collide and stick together

instead of bouncing (making droplets)• Condensation occurs because of the cooling• Clouds form if the drops grow large enough or

are seeded with particles

Clouds and Fog

• Mountain simulation

• http://www.public.iastate.edu/~abc/java/mtnsim/mtnsim.html