Unit #1

Activity 12
Shake it Up Baby - Crank the Heat

Activity Overview

Temperature is a measure of the average kinetic energy of the atoms of a substance while heat is the total kinetic energy of those atoms.

Students use a computer simulation to discover the connection between temperature and kinetic energy [energy of motion]. The computer simulation shows a box divided into two sections by a wall that can be removed. Students can then fill either side of the box with molecules of varying mass. They can also adjust the temperature of either box. Graphs show the average kinetic energy of atoms in each partition. Students are asked to experiment with the various options for adjusting the temperature and/or mass in either partition. Students can also remove the partition so that atoms from either side can mix.

Learning Objectives

Students will:

• Describe by using references to a computer model that temperature is related to the average kinetic energy of atoms in a container.
• Evaluate when a system has reached thermal equilibrium by mixing two groups of atoms with different temperatures and indicating when thermal equilibrium has been reached.
• Distinguish between the terms heat and temperature.

Conceptual Prologue

Macro-Micro Connection

In this activity students will see the connection between heat, temperature, and the kinetic energy of atoms. As the burner heats the air at the mouth of the balloon, a cascading affect of heating up molecules near the burner, causing those molecules to move faster due to their increase in kinetic energy. These fast moving, hot, molecules bump into those nearby and so on, until the heat energy (which is just a bunch of moving molecules) raises the temperature throughout the balloon.

Other macro connections:

• “Room temperature” occurs because of the way atoms and molecules transfer energy to each other through collisions. The transfer of kinetic energy is actually a transfer of heat energy, so the temperature of everything that is in contact with everything else eventually becomes equal, reaching thermal equilibrium.
• Because people are not at room temperature, there must be some other process going on inside our bodies to prevent this from happening.

Science Concepts

Each atom has a certain amount of kinetic energy. This energy fluctuates due to the many collisions with other atoms. However, when two atoms collide transferring kinetic energy from one to the other, no kinetic energy is lost. If the amount of kinetic energy for each atom is added up then you would have a value representing the heat energy of that collection of atoms. It follows that the more atoms which are counted, the greater the heat energy will be.

Temperature is a measure of the average kinetic energy of those atoms. The result of this difference between heat and temperature causes the number of atoms measured to play a major role in understanding how much heat energy an object has at a particular temperature.

For example, if two glasses of water are left out on the table, one completely full and the other exactly half full, they will eventually both come to room temperature, about 21°C. They may have the same temperature, but the full glass has twice the heat energy of the half full glass. Because the full glass has twice as many molecules each carrying some heat energy (or kinetic energy) the full glass has more heat at the same temperature.

The higher the temperature the faster the atoms move.

Large objects can have a kinetic energy and temperature which are distinctly separate things. For example, a baseball sitting still has no kinetic energy, but its atoms are moving, so they have kinetic energy. Because the temperature of a substance is due to the average kinetic energy of its atoms, the ball does have a temperature. Depending on how many atoms it takes to make up the ball, it has a certain amount of heat energy (the total energy of the atoms comprising the ball).

An atom, however, can't separate kinetic energy from heat energy. For atoms they are one and the same thing. A bunch of atoms sitting still have no kinetic energy, no heat energy, and would have zero temperature (on the Kelvin temperature scale).*

In summary:

• For an atom Kinetic Energy = Heat Energy
• For a substance Heat Energy = Total of all the Kinetic Energies of its atoms
• For a substance Temperature = Average Kinetic energy of its atoms

*Because temperature is a function of the average kinetic energy of the atoms, the lowest possible temperature would be when the atoms stop moving, therefore having no kinetic energy. Because there is a lowest possible temperature, it would make sense to use a temperature scale that starts at zero. This temperature scale is called the Kelvin temperature scale and zero Kelvin is a special temperature called absolute zero (when all atomic motion is stopped).

Naive Conceptions

• Heat is a substance.

Heat is not matter. Heat is just a manifestation of the motion of atoms.

• Heat and temperature refer to the same thing.

Heat and temperature are very different. Heat energy is the TOTAL kinetic energy of a group of atoms while the temperature is the AVERAGE kinetic energy of those atoms.

Activity Design and Execution

Major Science Concepts:	• heat vs. temperature • thermal equilibrium
Assumed Previous Knowledge:	• That atoms and molecules are in continual motion. • An understanding that kinetic energy [energy of motion] depends on mass and velocity. • An understanding of how a running average is calculated.
Time:	• Approximately 50 minutes
Materials:	• Computers with Workbench Software
Advanced Preparation: (if any)	• None

Investigative Question: What is temperature, and how is this different from heat?

1. Using Workbench software open the "Heat vs. Temperature" activity.
2. The software will then show a box with the ability for the user to change the speed of the atoms, as well as change the number of atoms in the box. A graph will show the total and average kinetic energy in the box. There will also be a temperature gauge attached to the box.
3. The software will then ask students to do the following:
   - Change the speed of the atoms and look at how it changes the temperature of the atoms.
   - Experiment with different numbers of atoms and speeds of atoms to determine which measurement better correlates to the temperature - total kinetic energy or average kinetic energy.
4. The software will then ask students to explain which is a better measure of temperature, total kinetic energy or average kinetic energy and to explain why.
   
5. The software will then explain that heat energy is the same as the total kinetic energy, that temperature is the same as the average kinetic energy, and that they should use the terms heat energy and temperature to answer the remaining questions in this unit.
6. The software will then show a larger box with a partition that separates the box into two boxes. It will then challenge the students to place an equal number of atoms heavy atoms in container A as light atoms placed in container B and then make their temperatures equal. The software will then ask the students what they notice about the heat energy (total KE), temperature (average KE), and speed of the atoms in each container.
7. The software will then challenge the students to create a situation when there are atoms of the same mass in each container. However, they can only have half as many atoms in one container when compared to the other. They must also make both containers have the same temperature. When they achieve this the computer will ask them to explain their setup.
8. The software will then place an equal number of heavy atoms and light atoms in the two separate containers. All of the atoms will have the same velocity. The software will then ask the students to compare the heat energy, and temperature of the containers and explain why they observe what they do.
   
9. The software will display a partitioned box with light molecules on one side and heavy molecules on the other side. It will then ask students to:
   - Predict what you would need to do in order to make the atoms on each side have the same velocity [speed].
   - Adjust the controls to make it happen.
   
10. The computer should offer all the same options mentioned above with liquids and ask about differences between liquids and gasses.


11. The computer will then allow the user to remove the partition and ask the students to note what happens to the kinetic energy [energy of motion] when two substances mix together. They will then be asked to determine when the system reaches thermal equilibrium and to describe how they knew it reached this point.
12. Have a discussion with students about their observations and the concept of thermal equilibrium [a state in which all atoms in a mixture have the same average kinetic energy or energy of motion]. Previously, thermal equilibrium was described as "when the kinetic energy is even spread out". We can more concisely say that thermal equilibrium is when the temperature of the atoms becomes stable.

Assessment

Have students write several things in their notebooks:

1. What is the difference between heat and temperature?
2. Compare a cup of water to a gallon jug of water. Assuming they are the same temperature, the heat energy would best be compared in which way: they have the same heat energy, the cup of water has more heat energy, or the gallon of water has more heat energy.
3. Explain why everything that is left out on the counter becomes room temperature. Describe what is happening at the atomic level.
4. Do you think the atoms inside the flame of the hot air balloon burner are moving fast or slow? Why?
5. How does the heat that is generated by the burner spread out through the entire balloon?
6. Why does the balloon cool down? Explain what happens at the atomic level.
   

Internal Notes:
• See computer lab E