Using a D-cell battery, a rubber band, some wire, a motor, and a propeller, I showed how chemical energy in the battery can be changed to electrical energy (through the wires). This then made the propeller spin which was a change to kinetic energy.
After this, I showed how the battery's chemical energy and the electrical energy from the wire could be changed to sound energy by connecting the battery and the wire to a buzzer.
Finally, I showed how chemical energy can be changed to heat (thermal) and light (radiant) energy. All we had to do here was light a candle.
The candle's thermal energy provided a nice segue into today's topic: Temperature and heat. I showed a transparency which had the three states of matter: solid, liquid, and gas, and how the particles in each of these states move. The students learned that solids have particles that are tightly packed together and are unable to move very quickly. Particles in liquids are a little more loosely packed so they can move around a bit more and are also able to move faster than those in solids. Gases have particles that are spaced far apart and move very quickly.
We used this to discuss kinetic energy. While we can't see the particles in a desk or a book move, they are constantly in motion! That desk or book, then, have kinetic energy. The faster those particles move, the more kinetic energy the object has.
Here's how kinetic energy relates to temperature. In science, temperature is the measure of the average kinetic energy of the particles in a sample of matter. Basically, as the particles in an object move faster, their kinetic energy becomes greater and the temperature of the object increases. I asked the students if they thought the particles in a mug of hot tea or those in a glass of iced tea moved faster.
The students were then asked if they thought temperature and heat are the same thing. Heat is the type of energy while temperature is the measure of that energy.
We moved on to complete a few experiments on temperature and heat.
"Hot Band" - This was a very simple lab but it demonstrated the concept. Each student was given a rubber band. They placed the rubber band against their forehead and described the temperature of the band. They then stretched the band and placed it back against their forehead and then told how it felt different. The students noticed that the stretched band felt warmer. When the students stretched the band (using mechanical energy), they caused the particles in the band to move farther apart. This increased the kinetic energy of those particles and allowed it to be transferred to heat or thermal energy.
"Smoke Rings" - This lab showed the downward flow of cold water through warmer water.
We used a bowl, a baby food jar, some food coloring, a piece of aluminum foil, cold water, and warm tap water. I filled the baby food jar with cold water and then added an ice cube to chill it further. The bowl was filled with warm water. We removed the ice cube from the baby food jar and added 7 drops of red food coloring. I then covered the jar with the foil, held it in place with a rubber band, and used a pencil to poke a hole in the foil. We turned the baby food jar over and placed it in the bowl so the top of the jar was just below the surface of the water. The students then took turns tapping the bottom of the jar.
The students observed the cold water from the baby food jar flowing down through the water in the bowl. When we looked really closely, we saw the cold water coming out of the baby food jar in spurts and then dispersing a little (it is supposed to look like rings, hence the name of the lab). The particles or molecules in the cold water are closer together than those in warm water so the cold water weighs slightly more. This makes the cold water sink to the bottom of the bowl of warm water.
"Puff Signals" - This experiment also involved hot and cold water. However, rather than showing cold water moving through warm water, this one showed hot moving through cold.
For this, we used two large-mouthed glass jars. We also needed more red food coloring, a baby food jar, aluminum foil, and 5 ice cubes. We placed the ice cubes in one of the large jars and then filled the jar with cold water. The baby food jar was filled with hot water and 7 drops of food coloring were added. Again, the baby food jar was covered with some foil that was held on with a rubber band. The baby food jar was then placed inside the empty large jar. I removed the ice cubes from the cold water in the other jar and then poured the water into the jar holding the baby food jar. We used a pencil to make a hole in the foil and then used the blunt end of the pencil to tap the foil.
The students saw the hot water puff up out of the baby food jar. As was explained earlier, the hot water is lighter (due to the spacing of its molecules) so it is able to rise to the top of the cold water.
We had a little help from my friends Ben and Jerry for this next experiment. :)
I asked the students what they thought would happen if they placed an ice-cold spoon on top of a scoop of ice cream. I then asked what they thought would happen if a hot spoon was placed on the scoop. What about two hot spoons?
I placed a metal spoon for each student into a baggie of ice to cool it off. One metal spoon for each student was left out at room temperature. A third spoon for each child was heated in steam coming from a kettle. The students tried the room temperature spoon first and noticed little difference (unfortunately our ice cream was already a little melty but they didn't see it melting any more from this spoon). They then tried the ice-cold spoon and discussed what they saw. Last came the hot spoon which, as they had predicted, caused quite a bit of extra melting!
I explained what happened while the students enjoyed their ice cream. The hot spoon caused the ice cream to melt due to a transfer of energy from the spoon to the ice cream. When I placed the spoon in the steam, this caused the particles of the spoon to start moving faster which increased the temperature of the spoon. This energy was then transferred from the hot spoon to the cold ice cream. Two spoons would cause more melting since they have twice as much mass. The more mass an object has at the same temperature, the more thermal energy it has.
We finished up by trying out another lab to demonstrate the transfer of thermal energy. We didn't have much success with this one so feel free to try it out at home!
"Magic Coin" - For this lab each student needed a glass soda bottle and a coin that was larger than the bottle's opening (we used quarters). They also used a bowl of cold water.
The students held the coins and bottle mouths in the cold water for a little while. After removing the objects from the water, they placed the coin on top of the bottle opening. The students then grabbed the bottle neck with both hands and held their hands in place for several seconds. The coin will "jump" (one student actually got it to work).
Next week: Look forward to continuing our discussion of heat. We'll talk more about the flow of heat (build on what we saw in the ice cream experiment) and we'll also talk about exothermic and endothermic chemical reactions.
The "Magic Coin" lab came from this website:
http://www.kids-science-experiments.com/magiccoin.html
The lab "Hot Band" is from Physics for Every Kid.
VanCleave, J. (1991). Physics for Every Kid: 101 Easy Experiments in Motion, Heat, Light, Machines, and Sound. San Francisco: Jossey-Bass.
The labs "Smoke Rings" and "Puff Signals" are from Chemistry for Every Kid.
VanCleave, J. (1989). Chemistry for Every Kid: 101 Easy Experiments That Really Work. San Francisco: Jossey-Bass.
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