Convection

4-2

Uneven Heating Questions What causes Earth’s surface to heat

up? What are some of the variables that

cause uneven heating of Earth’s surface?

What happens to the temperature of equal volumes of soil and water when they are place in the sunshine for 30 minutes?

Density What will happen to these objects

when I drop them into the water? Object Results

– Floats - less dense than water– Sinks - denser than water

Which objects are less dense than water?

Which objects are denser than water? Is water denser or less dense than

cork? Is a vial cap denser or less dense than

a penny?

Cold Water Challenge Do you think the blue ice water is

denser, less dense, or the same density as room-temperature water?

Challenge Procedurea. Fill vial with room temperature water.

Let stand 1 minute undisturbed.b. Use bulb pipette to take up bulbful of

blue cold water.c. Gently squeeze bulb to release blue

cold water on either the bottom or the surface of the vial of water. Use a steady slow squeeze.

d. Observe the vial carefully to determine if the cold water floats or sinks.

Observations• What happened to the cold blue water

when it was placed in room-temperature water?

• Why do you think the blue water went down?

• Is the blue ice water denser, less dense, or the same density as room-temperature water?

• What do you think will happen if you warm up the bottom of the vial where the cold water is sitting?

Hot Water Investigationa. Carefully place the vial with blue

water on the bottom into a plastic cup.

b. Fill zip bag half full of hot water, using the syringe. Seal top of bag shut.

c. Slowly lower bag of hot water into the cup with the vial.

d. Closely observe the blue water carefully for 4 minutes.

e. Make accurate illustrations of movement of cold blue water. Write captions under each illustration.

Hot-Water Results• What happened to the cold blue water

in the vials after the hot water was placed beside it?

• Why do you think the blue water moved up?

• Why do you think warm water moves up?

• Why do you think the blue water started to sink after coming to the surface?

• What pattern did the blue water make after the hot water was added?

Vocabulary• Materials sink in water if they are

denser than water.• Materials float in water if they are

less dense than water.• Convection Current

• A circular current in a fluid caused by uneven heating

Content• Is hot water denser or less dense than room-

temperature water?• Hot water is less dense than room-temperature

water.• Which is denser, hot water or cold water?

• Cold water is denser than hot water.• What causes a convection current?

• Occurs when the bottom of a mass of fluid is heated. Warm water rises, cools, and then descends, creating a circular flow.

• Your questions?• Homework: Read Wind! Pg. 202-207 and

answer questions.

Wind! Questions Explain how convection currents are

produced in the air. Explain what causes wind. Describe what happens to air

molecules when air is heated. What is the source of energy that

causes the wind to blow?