Convection

• Convection– The transfer of thermal energy in a fluid by the

movements of warmer and cooler fluid.

• Demo– Red is hot– Blue is cold

Convection Demo

• What happened when the two waters were added?

• Why did the two waters act that way?

Conduction

• Have you heard of conduction?

• Conduction– The transfer of thermal energy by collisions

between the particles.

• Which spoon handle will be hot?

• Why?

Radiation

• What is radiation?– The transfer of energy by electromagnetic

waves.

• What can matter do to radiation?– Absorb the energy– Reflect the energy– Transmit the energy

Radiation

• Solids, liquids or gases

• Which do you believe radiation moves more easily through?

Convection in Gases and Liquids Lab

• Introduction:– Birds use a large amount of energy to flap

their wings. Many combine flapping flight with gliding through the air. Some birds conserve energy with soaring flight. For example, a hawk rarely flaps its wings as it circles high overhead on a warm, sunny day. Soaring birds use convection currents to stay aloft.

Convection in Gases and Liquids Lab

• Objectives:– Observations convection currents formed in

water.– Observe convection currents formed in air.

• Materials:500 mL beaker Water Scale

Black pepper Hot plate

Candle Small piece of paper

Convection in Gases and Liquids Lab

• Pour 300 mL of water into the beaker.• Weigh out 1 g of black pepper, using the

small piece of paper as a weighing boat.• Sprinkle the pepper into the beaker of

water. Let it settle to the bottom.• Heat the bottom of the beaker using the

hot plate. DO NOT BOIL THE WATER.• Observe how the particles of pepper move

as the water is heated. Make a drawing showing the pepper’s motion.

• Turn off the hot plate.

Convection in Gases and Liquids Lab• Light the candle and let it burn for a few

minutes.

• Blow out the candle. REMAIN STILL. Observe the motion of the smoke.

• Make a drawing of the smoke.

Convection in Gases and Liquids Lab• Discussion:

– Describe how the particles of pepper moved as the water became hotter.

– Discuss how the motion of the pepper particles is related to the motion of the water.

– Describe how the smoke particles moved when the candle was blown out.

– Explain how the convection currents that you formed in this lab are similar to the convection currents on which birds glide.

– Form a hypothesis that explains how the convection currents on which birds glide form.