Density and Convection­2010 Period 1.notebook
October 19, 2010
What is radiant energy?
How does radiation affect the surface of Earth?
• Radiation is energy that passes through space.
• Earth receives radiation from the Sun.
Visible light is the main kind of energy from the Sun that heats Earth. Energy is transferred when light energy is absorbed by molecules in Earth's surface, causing them to move faster, which increases the temperature. Think about walking barefoot on a sidewalk on a hot day....
• What did you feel?
• Why did your feet get hot?
• How did heat transfer from the cement to your feet?
Heat is motion of atoms and molecules. The greater the motion, the more heat energy there is in a solid, liquid, or gas.
Energy transfer happens between molecules or atoms when they come in contact.
This kind of heat transfer is conduction. Heat can transfer by conduction from atom to atom in a material, or between two different materials when their atoms or molecules make contact. Have you ever reached for a metal spoon that was in a pot of cooking soup? If so, you might have been surprised to find that it was really hot. But the spoon handle hadn't been in the soup or in a fire. • How did the spoon handle get so hot?
• Could heat conduct through an object?
• How could we find out if conduction is a possibility?
May 24­6:31 AM
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Density and Convection­2010 Period 1.notebook
October 19, 2010
Title: Conduction, What's your Function?
Problem: How does heat energy move through materials?
Background Information: • Conduction‐Heat is transferred from one material to another
when they come into contact.
• Heat is transferred from the hotter material to the colder
material until the materials reach the same temperature.
Hypothesis: If 2 metal bars (steel and aluminum) are placed in hot water then the _________________bar will heat the fastest, because________________________________________________.
Materials:
• 2 metal bars with temperature strips (steel [heavier] & aluminum [lighter]) • Large clear cup
• Foam cup
• Hot water from hot pot Temperature strip
This is a liquid­crystal temperature strip. The crystals sealed inside turn color when they reach a certain temperature. Different crystals produce their color at different temperatures.
When the temperature is below 30 degrees Celsius, the temperature strip will not show any color. If the temperature is above 36 degrees Celsius, the strip with not show any color. It will only show color between 30­36 degrees. The temperature strips and the metal bars might provide information about conduction through one kind of material. Procedures:
1. Fill the foam cup ½ full of water, place in the clear plastic cup.
2. Place metal bars in the hot water, keep temperature strip out of the water.
3. Determine which bar heats faster.
4. Record which bar heated the most quickly and answer summary questions.
Summary Questions: 1. Feel the two metal bars. How did heat get from the hot water to the temperature strip far above the water level?
2. Draw an energy diagram for heat transferring from water to the metal. 3. Draw an energy diagram for heat transferring from the bottom of the metal bar to the top.
4. Which metal is a better conductor? Why do you think so?
5. Compare your hypothesis to the results of heating the metal bars. How was it similar? How was it different?
6. List 3 new examples of heat transfer not discussed/read in class. Label what type of heat transfer they are (conduction or radiation). 7. How does conduction heat the atmosphere & Earth? (Hint: Look on page 24, Weather and Water book)Weather and Water book)
May 24­6:37 AM
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Density and Convection­2010 Period 1.notebook
October 19, 2010
Summary Questions: 1. Feel the two metal bars. How did heat get from the hot water to the temperature strip far above the water level?
The heat energy in the water molecules transferred to the molecules in the metal by conduction. The heat conducted from molecule to molecule in the metal to move up the bar.
2. Draw an energy diagram for heat transferring from water to the metal. Conduction
Thermal energy
Thermal energy
3. Draw an energy diagram for heat transferring from the bottom of the metal bar to the top.
Conduction
Thermal energy
Thermal energy
4. Which metal is a better conductor? Why do you think so?
Aluminum conducted better. The heat moved up the bar faster and went further. 5. Compare your hypothesis to the results of heating the metal bars. How was it similar? How was it different?
6. List 3 new examples of heat transfer not discussed in class. Label what type of heat transfer they are (conduction or radiation). • Fireplace warming person‐radiation
• Sun warming person‐radiation
• Person swimming in ocean‐conduction • Warm shower‐conduction
7. How does conduction heat the atmosphere & Earth? (Hint: Look on page 24, Weather and Water book)
• The air molecules in the atmosphere are heated by conduction when they contact Earth’s heated surfaces.
• Earth is heated by conduction when hot water and carbon dioxide molecules in the atmosphere come in contact with the surface of Earth. May 25­6:55 AM
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Density and Convection­2010 Period 1.notebook
October 19, 2010
Radiation and Conduction Review
• Reviewing what we have learned about energy transfers so
far...
• Light is one type of radiation we get from the sun.
• Radiant energy travels through space as waves.
• Visible light, ultraviolet, and infrared radiation are
responsible for most of the heating of Earth’s surface.
• When the sun’s radiant energy hits Earth’s surface, some of it
is absorbed. Molecular motion of the material increases.
• Molecular motion is heat.
• Heat can transfer from one material to another when they
come into contact through conduction.
• The atmosphere is heated by conduction when air molecules
contact Earth’s surface, and by reradiation from Earth’s
surface.
• Heat transfers from a warmer to a cooler area or material.
• What is the last way energy can be transferred?
• Convection
Mar 12­6:06 AM
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Density and Convection­2010 Period 1.notebook
October 19, 2010
What is convection?
Read Convection Reading page 32.
Convection occurs only in fluids (gases and liquids), where molecules are free to flow. • Hot = less dense = rise (move upward)
• Cold = more dense = fall (move downward)
Mar 11­4:31 PM
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Density and Convection­2010 Period 1.notebook
October 19, 2010
Convection Chamber Demonstration
• Today we’re going to try to use a chamber as a model to
explore how convection works in the air.
• The air in the basin is a model of the atmosphere.
• A candle at one end represents a hot location on Earth’s
surface.
• Ice on the top of the chamber will represent the cold
temperatures high in the atmosphere.
• Incense smoke introduced into the system through the large
hose will allow us to see what is happening in the air.
• We’ll use a flashlight to help observe what is happening.
Part 1:
1.) Before we start, please draw on your lab worksheet what you
think will happen during the demonstration.
2.) Also, describe why you think this is going to happen. Make
sure you discuss how density and the transfer of energy is
involved.
Part 2:
Draw what you observed during the demonstration.
What did we observe?
We observed flowing smoke down the hose, across the bottom of
the chamber, up to the cover above the candle, across the cover,
and back down with the incoming smoke.
3.) Explain how convection occurs in the Convection Chamber.
• The smoke was cold (more dense) because of the ice, which made it travel down. • The smoke/air moved across the bottom to the candle, which heated them (radiation and conduction). • The heated, less dense air rose to the cover, where it transferred heat to the cover (conduction). • The denser, cold air moved downward with the incoming new smoke to complete the cycle. Mar 11­4:50 PM
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Density and Convection­2010 Period 1.notebook
October 19, 2010
4.) Draw 2 energy diagrams involving the Convection Chamber.
___________Heat Transfer
___________Heat Transfer
Energy Source Energy Receiver
Energy Source Energy Receiver
• Read page 33
Convection Cells in Earth's Atmosphere
5.) Explain heat transfers in a convection cell on Earth.
• Earth’s surface is heated by the sun. Air close to warm land or
water is heated by conduction and radiation.
• The warm air rises because it is less dense (convection).
• At high elevation, air radiates heat to the cold environment
and contracts.
• The dense air falls back to Earth (convection). The cold air
can be heated by the warm Earth to repeat the process.
• This cycle of air is a convection cell. Convection cells occur in
predictable locations around the planet. They play an
important role in global weather.
6.) Draw 2 energy diagrams involving a convection cell on
Earth.
___________Heat Transfer
___________Heat Transfer
Energy Source Energy Receiver
Energy Source Energy Receiver
Mar 12­6:23 AM
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Density and Convection­2010 Period 1.notebook
October 19, 2010
Conduction Investigations
Discussing the Results:
• What happened when the metal bars with temperature strips were placed in hot water? • How did heat get from the hot water to the temperature strip far above the water level?
• Did the metals conduct heat? Which metal is a better conductor?
Conduction Between Earth's Surface and Air:
The Sun shines on Earth and the air gets warm. How do you think that happens?
• Radiant solar energy strikes Earth's surface. The surface absorbs the energy.
• Molecules in the surface material increase in motion. Motion is heat, so the surface heats up.
• Molecules of the gases in the air come into contact with Earth's heated surface.
• If the surface is warmer than the air, energy from the surface will transfer to the air molecules. Air molecules will increase their motion. Motion is heat, so the air heats up.
Conduction is one way energy transfers to the atmosphere. When air molecules come in contact with hot surfaces, they receive energy and get hotter.
Reradiation:
There is another, even more important way that heat energy enters the atmosphere. It is called reradiation.
All matter radiates energy. It is one of the great truths of nature. Hot matter radiates more energy than cold matter.
When matter, like sand, soil, or water, absorbs energy from the Sun, it warms up. When the hot matter reradiates that energy, the matter cools down. That's why your containers of soil, sand, water, and air cooled down when you moved them into the dark/shade­they reradiated the energy they had absorbed from the light/Sun.
What happens to the reradiated energy? Most reradiated energy is not in the visible spectrum; it is in the infrared part of the spectrum. Infrared radiation is absorbed by water and carbon dioxide molecules in the atmosphere. The energized water and carbon dioxide molecules then transfer their energy by conduction (contact) to the oxygen and nitrogen molecules in the air to heat the whole atmosphere. Conduction Post­lab Questions
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Density and Convection­2010 Period 1.notebook
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Oct 18­2:13 PM
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