Post on 18-Jan-2018
description
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