Teacher Portal:
Heat and Heat Transfer
Investigation 3 – Concept Day
ZERO-IN
The italicized font represents information to be shared orally or physically completed with the students at this time.
The non-italicized font represents additional information included supporting the teacher’s understanding of the content being introduced within the CELL.
ASK WHY
Remind students that heat, thermal energy, and temperature greatly influence the way we live. We monitor our body temperature, dress for the hot and cold, build homes, schools, and cars with heating and cooling systems, and passionately search for alternative fuels as the threat of global warming takes hold. To live safely and productively, it is important to understand the thermal behaviors that govern our bodies and the world.
BRANCH OUT
Explain to students that climatologists monitor data from several Earth-observing satellites that act as thermometers in space. Using satellite data, they can create a record of land surface temperatures all over the world.
PRINT IT
Use your browser to download a printable PDF as help during the slide presentation and to make additional notes. In your browser, go to File > Print and then choose to save as PDF.
NAVIGATE IT
Once the slide presentation is launched
- use your left and right arrows to advance or go back in the slide presentation, and
- hover your mouse over the left edge of the presentation to get a view of the thumbnails for all the slides so that you can quickly move anywhere in the presentation.
- Click HERE to launch the slide presentation for the CELL.
SHARE IT
SLIDE HEAT-3-1
- Inform students that during this Investigation they will explore the specific heat capacity of materials and the transfer of heat.
Note: It is important for students to clearly establish the correlation between temperature and the motion of molecules in a substance.
- Remind students that
- the energy of motion is called kinetic energy,
- the higher the temperature, the higher the kinetic energy and the more molecular motion occurs,
- molecules vibrate with kinetic energy,
- the amount of vibration and movement is related to the amount of kinetic energy they have, and
- increasing the temperature of a substance increases its kinetic energy.
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SLIDE HEAT-3-2
- Read the slide to the students.
- Explain to students that the next two slides will attempt to answer this question.
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SLIDE HEAT-3-3
- Draw students’ attention to the surface of the cookie in contact with the cooler air in the kitchen.
- Tell students that the square in the upper right is an enlarged view of this surface, with the cookie on the left and the kitchen air on the right.
- Explain that the “cookie molecules” are moving much faster than the air molecules in the kitchen. This is because there is more kinetic energy in the hot cookies than the air.
- Explain that heat energy is transferred from the cookie to the air, from the direction from higher to lower kinetic energy.
- Tell students that the same type of energy transfer occurs when we go outside on a cold winter day. The higher kinetic energy from our bodies is transferred to the outside air, which has lower kinetic energy.
- As stated in the note in the lower right, heat energy is always transferred from areas of higher temperature to areas of lower temperature, NEVER the other way around.
- Draw students’ attention to the square at the bottom. Tell students that it depicts the situation that exists at the cookie surface once it has cooled. Heat stops transferring from the cookie to the kitchen air once the temperature of the two is the same.
- Explain to students that while the kitchen air started at 22oC (a typical room temperature), it would be very slightly warmer at this point. The air molecules would, therefore, move slightly faster than before the cookies cooled and transferred much of their kinetic energy to the air.
Note: The reason that the cookie did not raise kitchen air temperature more is that there is so much air volume in the kitchen compared to the mass of the cookie. This is why, later in this discussion when speaking about specific heat capacity, we will need to consider the mass of the substances we analyze.
Note: IT IS ESSENTIAL that students do not conclude from this discussion that the actual cookie molecules leave the cookie and enter the kitchen air! Just as in the case when a thermometer was placed in hot water in Investigation 1 and kinetic energy was transferred to the glass and then into the fluid inside the thermometer, it is a transfer of energy, not molecules. The molecules in the hot cookie are shown to move fast because of high levels of kinetic energy. When the kinetic energy leaves the cookie and enters the kitchen air, the cookie molecules slow down. They are still in the cookie.
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SLIDE HEAT-3-4
- Read the slide to the students.
- Remind students of the Law of Conservation of Energy, which states that energy cannot be destroyed or created. Therefore, all of the excess heat and energy from the cookie MUST be transferred to the air in the kitchen.
- Explain to students that even if we cannot feel the difference in temperature in the kitchen due the cooling cookies, the energy is nonetheless being transferred to the air.
- Tell students that if we were to hold our hand directly over a hot cookie when first taken out of the oven, we would be able to feel the heat “radiating” from its surface. We would certainly feel the heat transfer if we were too quick to bite into the hot cookie and burn our mouth!
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SLIDE HEAT-3-5
- Inform students that this slide introduces the concept of specific heat capacity.
- Read the slide to the students.
- Tell students that specific heat capacity is a physical property of matter.
Note: In this slide, the temperature of a 1 gram cube is shown to increase from 25oC to 26oC. The amount of heat (in Joules) required to do this would be this substance’s specific heat capacity.
- Tell students that they will perform an experiment in Lab in this Investigation to determine the specific heat capacity of a substance.
Note: They will do so again in the Performance Assessment for this Investigation.
Note: As stated on this slide, a higher specific heat capacity means that it takes more heat to raise the material’s temperature. As might be guessed, the ability to resist temperature increase by a substance would tend to make it a good heat insulator. In the next slide, we will see how the space Shuttle is protected from heat damage by tiles that act a insulators.
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SLIDE HEAT-3-6
- Inform students that this slide essentially presents some facts and statistics about the Space Shuttle.
- Explain to students that in outer space, that is outside the Earth’s atmosphere, there are no molecules. As the spacecraft prepares to reenter the Earth’s atmosphere it is moving at about 27,000 Km/hour. There is not a problem caused by friction outside the atmosphere because, again, there are no molecules to strike the Shuttle’s surface and cause friction.
- Tell students that this situation changes when the Shuttle reaches the Earth’s atmosphere where gas molecules are present. The entire bottom surface of the spacecraft scrapes against trillions of gas molecules at incredible speed and thus generates immense heat due to the friction produced.
- As shown, tens of thousands of small tiles are glued to the lower surface of the Shuttle, the surface that makes direct contact with the atmosphere at reentry.
- Direct students’ attention to the the bottom of the slide, where a single tile is shown.
- Explain to students that each tile is somewhat larger than a human hand and made of a lightweight foam material consisting of 90% air and 10% silica fibers, glazed with a coat of borosilicate.
- Tell students that on the next slide, we will see why these particular materials were used to manufacture the heat-protecting tiles.
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SLIDE HEAT-3-7
- Inform students that this slide shows the specific heat capacities of a number of substances including materials that go into the manufacture of the Shuttle heat tiles.
- Explain to students that the three main components of the tiles, air, boron, and the silicon all have relatively high specific heat capacities. Thus, these relatively thin tiles are able to keep the skin of the Shuttle at somewhere around 300+oC, even though only a few centimeters away the temperature is over 1,600oC. Amazing!
Note: At this point, it might be interesting to ask students if they think that water would be a better insulator than the air, silica, and borosilicate. Clearly, from the table on this slide, water has a much higher specific heat capacity than any of the materials that are present in the tiles. The class might discuss the problems (perhaps including weight) of protecting the Shuttle with water.
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SLIDE HEAT-3-8
- Inform students that this slide illustrates the logic of the steps involved in the Lab for Investigation 3.
- Explain to students that:
- A metal cube will be placed in hot water of a known temperature so that it acquires that temperature as well.
- It is then transferred to cooler water of a known temperature and students will then observe the increase in temperature of that water sample.
- The water temperature increases as heat is transferred from the metal cube to the water that surrounds it until both the water and cube are at the same temperature.
- Tell students that they will use data obtained from this experiment to calculate the specific heat capacity of two cubes made of different metals.
Note: In Lab, these experiments will actually be conducted in Styrofoam cups to reduce heat loss to the air.
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SLIDE HEAT-3-9
- Inform students that this final slide once again emphasizes the importance of goggles when heating glass in the Lab.
- Remind students to use tongs to move hot metals if necessary.
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