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Energy and Temperature
Indiana Science Indicators Addressed:
2.1.2 Use tools, such as thermometers, magnifiers, rulers, or balances, to gain more information about objects.
Investigate, observe, and describe that when warmer things are put with cooler ones, the warm ones loose heat and the cool ones gain it until they are all at the same temperature.
Demonstrate, using drawings and models, the movement of atoms in a solid, liquid, and gaseous state. Explain that atoms and molecules are perpetually in motion.
8.3.10 Explain that increased temperature means that atoms have a greater average energy of motion and that most gases expand when heated.
The Student Will Be Able to:
Explain why our sense of touch is not a good indicator of the temperature of an object.
Describe the effect of temperature on the internal movement and size of liquids and gases and understand that added energy is needed to change the temperature or state of matter.
Explain the movement of particles in solids, liquids, and gases.
Describe that when two objects of a different temperature are put together the cooler one will rise in temperature and the warm one will lower in temperature until they are at the same temperature, and the change in temperature of each depends on the physical size of each object.
Describe how a thermometer works.
Three large beakers or small pales big enough for hands to go into, water, mechanism for warming and cooling the water (hot plate, ice, etc.), food coloring, Mylar balloon, hairdryer, ping-pong balls, clear plastic containers, clear plastic straws, tape
All materials, including solids, have motion even when they are “standing still”. This motion is located in very tiny vibrations between the atoms and the movement of the electrons around the nucleus of the atoms. As energy is absorbed by the material, the vibrations between the atoms become great enough to disrupt the structure of the solid and it will melt. As more and more energy is absorbed by a sample, the vibrations and now collisions between two molecules become great enough that some molecules can leave that sample as gaseous vapor.
The previous paragraph not only quickly describes how solids, liquids and gases vary from each other, but shows the intricate relationship between energy and temperature. Temperature is a measurement of the average kinetic energy that a sample has. That is, as the sample has more kinetic motion in it, the higher the temperature that can be observed. Likewise, as the kinetic energy decrease, the observed temperature is lower. Scientist have postulated that the coldest temperature that could be theoretically possible is approximately -460 degrees Fahrenheit which is -273 degrees on the Celsius scale. This low temperature is referred to as absolute zero, the point where there would be zero kinetic motion. To date, laboratory experiments have produced conditions very close to this temperature, but the constraints of physics prevent this condition from being observed.
Some of the kinetic energy of one material can be transferred to another material. Heat is this transfer of kinetic energy. It has been observed that the transfer of heat is from a source with more kinetic energy to a specimen of lower kinetic energy. When our hand is placed in a sample that has more kinetic energy, heat is transferred from the sample to our hand and it feels warm to the touch. However, when the sample has less kinetic energy then our hand, heat is transferred from our hand to the sample and therefore it feels cool to the touch.
When a specific number of molecules are contained within a specific area, other properties of the kinetic theory can be observed. These further concepts of the kinetic theory are most easily seen in gases, so we will limit our discussion here. As molecules gain energy and become more energetic, they vibrate more and more eventually pushing themselves away from each other. Since the molecules are contained, they bounce off the inside of the container. Now, when more heat is transferred to these molecules, they move more energetically, colliding with other molecules and the inside of the container with more force. If the container is solid, the pressure inside the container goes up. If the container is flexible, such as a helium balloon, the pressure of the gas inside will expand the balloon (increases its volume) until the pressure inside and outside the balloon are equal. Eventually, since density is a relationship of mass to volume (D=m/V), as the volume increase and the mass (contained in the balloon) doesn’t change, the density becomes smaller and floats on the more dense air outside the balloon.
The expansion of a gas as energy is transferred into it is very similar to how a thermometer works. When a liquid thermometer is placed into a substance, heat is transferred from the warmer to the cooler. If the warmer substance is the one being measured, energy is transferred into the liquid in the thermometer, which pushes off of each other more and begins to rise up the thermometer. When the thermometer and the substance reach a constant temperature, the column stops rising and the temperature can be read. If the thermometer is warmer then the sample, heat is transferred from the thermometer and the liquid in the thermometer condenses down. Early thermometers were large and open to the air. By closing the thermometer and trapping a gas above the liquid, the thermometers were more easily calibrated and therefore more accurate in repeated measurements. Also, the liquid used in today’s thermometers, primarily ethyl alcohol (ethanol), will vaporize if exposed to air.
An interesting phenomenon occurs during the measurement of temperatures using a thermometer. You may have noticed that when a thermometer is inserted into a sample, the thermometer will either gain or loose heat in the process. This heat has to either come from or go to the sample being measured. Therefore, by measuring the temperature, we actually change the samples temperature. Because of this, the measured temperature is slightly different from the true value. However, to minimize this effect, scientists use small thermometers in comparison to large samples. That way, the energy needed to change the thermometer is an extremely small proportion of the energy in the sample. This also explains why absolute zero has not been observed in the laboratory. If a sample could be cooled to such a low temperature, the thermometer that would be used to observe that temperature would transfer heat to the sample and therefore warming it above absolute zero. It’s a catch-22.
Engagement Activity:
Prior to class, warm up a beaker of water to a temperature that is warm but comfortable to put your hand in. Also cool another beaker of water to the same specification. Lastly, have a room temperature beaker of water that is large enough for both hands to go into. Arrange the beakers so the room temperature water is in the middle.
Ask the students what they feel when they put there hands on something cold? Hot?
Ask for a student volunteer. Have the student put one hand in the warm water and one in the cold water. Have the student describe to the other what he or she is feeling.
Now have the student put both hands in the room temperature water. Have the student explain what he or she is feeling to the rest of the class.
Explain to the students that our hands feel temperatures that are relative to its own. So if our hands are cold and then touch something that is any bit warmer but still pretty cold, they tell our brain that it is a warm object. This also works for hot and warm objects.
Allow other students to perform the exercise as time allows.
Engagement Activity:
Prior to doing this activity, have three beakers one each of hot water, room temperature water and cold water prepared.
Tell the students that you will be adding a couple drops of food coloring to each beaker. If each beaker is at a different temperature, what will happen to each of the food colorings? Will they all mix evenly at the same time?
Have one or two students come up to closely observe the beakers.
Quickly add one or two drops to each beaker. Adding to the hot water first will produce more desired results but could make some students suspicious.
Have the students announce when each beaker is evenly mixed.
What order did the beakers mix in? How does the temperature of the water affect the mixing?
Introduce to the students that the temperature of a substance tells us about how much energy of motion the substance has. Describe that even a solid material has small parts that are moving around such as electrons that move through a solid wire to produce electricity.
Engagement Activity:
Have a Mylar balloon (containing helium gas) that is optimally just deflated enough that it slowly sinks through the air at room temperature. (You can get these balloons at any card shop, flower store, etc. The first time you go and ask for a balloon this way they will look at you funny, but just explain that you’re a teacher and they will understand. It is recommended that you make friends with the owner/manager so that by keeping your balloon for next year, you only need a refill before repeating the exercise.)
Have a student describe to the class the state of the balloon. Some descriptions might be that it is flat, out of gas, empty (which it isn’t), sinks, doesn’t float, etc.
Now give the student a hair dryer set on hot. Have the student blow hot air on the balloon.
While this occurs have other students start to describe what they see and hear. Often they will see the balloon become tighter and begin to hear the folds pop out as the air inside expands.
Ask the students if more air is being added to the inside of the balloon. Make sure they understand that the gas that was inside the balloon before is still the gas inside it now.
Introduce to the students that as gases warm up, the gas move faster and faster, and that as they move faster they want to move away from each other. Therefore, when gases warm up they expand outward.
Explore:
Have the students do the Modeling Matter lesson which has been written as part of the PIE project.
Explore:
Perform the Heat Loss and Cool Gains lesson accessed from the Indiana State Standards Website. http://www.indianastandards.org/files/sci/sci_5_3_9.pdf
Explain:
Use this section to explain the core concepts to the students.
Elaboration:
To bring the concepts together, students will be building their own thermometers, calibrate them and then use them to find the unknown temperature of a beaker of water. The students will build a thermometer as described on the website, http://hop.concord.org/htu/htu.mess.act4.html, and as described on the student worksheet.
Prepare by having three beakers of water at different temperatures prepared before class starts. Once the students construct their thermometers, they will calibrate their thermometers by putting their thermometer in the coldest beaker and marking level of the water and will write down the actual temperature from an actual thermometer. Next, they will use the warmest water to make another mark on their thermometer and they write down what that temperature is. Lastly, they test the last water with their thermometers. Therefore the water to test should be between the temperatures they calibrated with. After they have their temperature, they can then take the actual temperature with the real thermometer.
Provide students with the activity worksheet included.
Monitor the students as they construct and test their thermometers.
Written by:
Dustan Smith, Aaron Debbink, and Jim Dyer; PIE Fellows, Ball State University
Partners ________________
________________________
Instructions: In this activity your group will make a thermometer and then use it to measure the temperature of a liquid.
Making the thermometer:
The materials you will need to make your thermometer are provided by your teacher. Follow all instructions that your teacher adds to the instructions below.
Put your straw into about two inches of water.
Fold down the top of the straw and tape it closed as shown in the picture below.
Have one student carefully put his or her finger on the bottom of the straw under the water.
Quickly turn the straw over keeping the finger on the side of the straw that is not sealed. It is okay if your straw thermometer does not have an air space above the water.
Now put the straw in the ‘warm’ water provided by your teacher. Also put a real thermometer in the water. Allow them to sit for at least two minutes. With a pen or pencil mark on the thermometer where the bottom of the water is. What temperature does the actual thermometer say? _____________
Now put your straw thermometer and the actual thermometer in the ‘cold’ water provided by your teacher. Let them sit for at least two minutes. Now mark the bottom of the water plug in your straw thermometer. What is the actual temperature from the real thermometer? _______________
Now you will estimate the temperature of another beaker of water without using the real thermometer.
Put your straw thermometer into the beaker of water provided by your teacher. Do NOT put the actual thermometer in. Allow the straw thermometer to sit for at least two minutes. Mark on the straw thermometer the bottom of the water.
Look at the other temperature marks and estimate what the temperature of this water is. It should be between the two other temperatures. The temperature is about ___________
Now use the real thermometer and find the actual temperature. What is the actual temperature? ___________ How close was your group from the real temperature? _____________
When you put the straw thermometer in the hottest water, the water plug in the straw was pushed up. What pushed the water up? _______________________________________
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