Convection

Convection in WaterInvestigation 5, Part 2

How heat is transferred….Radiant energy strikes Earth’s surface

The surface absorbs the energy

Surface molecules increase their motion

Molecules of air touches the heated surface of Earth

Energy is transferred from surface to the air

Heat in solidsMolecules are locked together

Absorbs radiant energy

Molecules begin to vibrate, continues through to the rest of the molecules creating heat

Heat in fluids (liquids and gases)

• Molecules are not locked into position

• Move around freely, toward, away from, or past one another

• Heat is transferred by one molecule touching another

Challenge of the Day

• Make layers of plain water that are different temperatures.

• Predict and record the colors of the layers on page 27 of your lab book.

Materials

• 3 vials (two with caps)

• 2 plastic-foam cups(to insulate cold and hot water)

• 2 pipettes

• 1 plastic cup

Procedure

1. Fill a vial

2. Create three layers in the vial– red, blue, and clearclear

Room Temperature Water

3/4 full

Warning!!!!!

• Do not bump or jostle an experiment in progress

How to successfully layer

Room Temperature Water

Wait for water to stop moving

How to successfully layer

Room Temperature Water

Wait for water to stop moving

Carefully introduce the blue water under the room temperature water

How to successfully layer

Room Temperature Water

Wait for water to stop moving

Carefully introduce the blue water under the room temperature water

Carefully introduce the red water on top of the room temperature water

Layered vial

• Stand for 5 minutes• Discuss with your partner what is

happening

Observations

• What happened in your vial after is sat undisturbed for a few minutes?– The red water starts to sink to the bottom of the vial

• What do you think caused the red water to start to descend?– The warm red water cooled– Increasing the density of the red water

Why?• Hot red water

layered on top of the room temp water because it was less dense.

• Cold blue water layered under the room temp water because it was denser

Less Dense

Denser

Heating the Layered Vial

• Create the 3 layered vial• Put 1 cm of hot water in a plastic cup• Place the layered vial carefully in the cup of

hot water and observe.

Heating the Layered Vial

• What did you observe?• How can you explain your observations?• Can you explain the energy transfer that

happened?

Observations:

• Heat transferred from the: - hot water to cold plastic- conduction - hot plastic to cold blue water- conduction - the blue water warmed , expanded, and started to rise- CONVECTION

Molecular Model

• Water becomes less dense as its temperature increases!

• As heat is absorbed by water, the molecules move faster and bang into each other with greater force and frequency. This drives the molecules farther apart. When molecules are forced farther apart, the water becomes less dense.

Convection

• When a mass of fluid is warmer or colder than the surrounding fluid, the mass will rise or sink in the surrounding fluid.

• This motion of masses is called convection!• This is the third way heat transfers.• Only happens in fluids where molecules are free to

flow

Convection

• The motion of masses or streams of fluid, due to difference in density resulting from temperature.

Reading

• “Convection” on pages 32-33