ACTIVITY #11: How Does Heat Energy Move?

Have you ever thought about being a firefighter or an astronaut? Maybe you know of someone who is a volunteer firefighter and

must spring into action when the fire whistle sounds. So what do a firefighter and an astronaut have in common? Both of them must have a good knowledge about how heat energy moves to do their job effectively and safely. The firefighter wants to keep the hot fire under control and wears protective clothing made from synthetic materials to protect him/her from the high temperatures of the fire. Fires can reach temperatures of over 1,000 degrees Fahrenheit! The astronaut on the other hand has to protect himself/herself from the extreme cold of outer space. The spacesuit is made of many layers, each serving a specific purpose, in order to protect the astronaut while in space. Space is a region of extreme temperatures.

        How does heat energy move?         Do some materials allow heat energy to move better than others?         What kinds of materials are used to construct spacesuits and firefighter gear? Where are they made?

GOALS: GOALS: In this lab activity, you will …          Learn how heat energy moves through solids.        Determine if heat energy moves equally well through different types of solids         Determine how heat energy moves through gases differently than it moves through solids.

Activity Overview:Activity Overview: A synopsis of this lesson is as follows…In this activity, we will look at how effectively heat energy moves through solids and gases. Drops of wax will be placed on solid rods made of different materials. One end of the solid rods will be ‘heated’ using candles, and the melting of the wax drops will be used to determine the rate at which the heat energy moves from one end of the rod to the other. Data for different materials will be compared to determine if heat energy moves equally well through the different materials. Hollow metal rods will then be tested using the same methods, and the results of the solid and hollow rods will be compared.

CONNECTIONSCONNECTIONS Heat energy is the total random kinetic energy of the particles in substances

If one part of a solid is at a higher temperature than another part, heat energy will travel through the solid, in a process called conduction. The heat energy always moves from parts of the solid that are at higher temperature to those parts that are at lower temperature. Heat energy moves through the solid, but mass does not move.

Heat energy moves through a liquid or a gas through a process called convection. The particles in a liquid are more loosely bound than they are in a solid, and can easily slide by each other. Because of this loose bonding, liquids can flow. The particles in a gas are not bound to each other, and are free to move throughout the space containing the gas. Gas particles move independently, but they constantly collide with each other

When a solid, a liquid or a gas receives heat energy and its temperature increases, the substance will expand. The particles that make up the substance stay the same size, but they are more energetic and take up more space. The mass of the substance stays the same, so when it expands, the density of the substance decreases.

Important Concept:

How do particles move in a solid? The strong connections between particles (called bonding) keep the particles in a solid object from roaming around within the solid. Each particle is held in place by the particles that surround it. Even so, the particles never remain at rest. The particles always have some kinetic energy. Each particle is confined to a point in the solid by the bonding, and because of its kinetic energy, it ‘wiggles’ or vibrates around this point. Particles in a solid can ‘wiggle’, but they cannot travel through the solid.

Besides holding the particles in place, the bonding serves acts like a link between the particles. If one particle is wiggling more energetically than nearby particles, it will transfer some of its kinetic energy to the nearby particles through the connecting bonds. When candles deliver heat energy to an object, the particles in the part of the object that receive the heat energy wiggle more violently. Their energy is passed from particle to particle and as a result, the heat energy moves throughout the object. It is important to understand that the heat energy moves from one end of the object to the other, but the particles do not. This process, where heat energy is passed from particle to particle without the particles moving from their place in the solid is called thermal conduction.

Part A - Conduction - The Movement of Heat Energy Through Solids

We will look at the ways that heat energy moves from one point to another point through a solid.  

Gather the following materials: 2 clothespins, 1 rod, 1 tea candle, 1 medium length candle, 2 wooden blocks, & something to light candles.

You will be working near open flames.  Do not reach over any lit candle.  Be very careful to tuck in loose clothing. Keep your hair away from the flames.

First prepare the rods for dropping wax on them. We will place a single wax drop on top of the rod in four spots. Use a permanent marker to place a mark, starting from one end of the rod, 2cm, 4cm, and 6 cm, (The 12cm mark should be about the middle of the rod) Light the long candle and drop a single drop of wax on the end of the rod, at the 2cm mark, at the 4cm mark, and at the 6cm mark.

One of the controlled variables in this investigation is the placement of the wax drops on the bars. Be sure to mark the rods accurately and carefully position the wax drops onto your marked points.

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Use two clothes pins to support the bars. The outside face of one clothes pin should be placed on the 12 cm mark, and the second clothes pin placed at the end of the bar opposite the wax drops.  Put small ‘tea’ candles up on two wooden blocks against the clothespin . After the candle has been lit for a few minutes carefully slide the candle and blocks under the bar and up to the clothes pin, so that the outer edge of the candle rests against the outer surface of the clothes pin. Place the flame of the candle directly under the bar so that the heat energy from the flame heats the spot on the bar that was marked at the 8cm point.

Materials Investigated Listing of Materials by Conductivity

(highest to lowest)steel 1. ____________________brass 2. ____________________aluminum 3. ____________________glass 4. ____________________hollow brass 5. ____________________

  hollow aluminum 6._____________________

Question #1: Which substance tested is the best conductor of heat energy, and which is the poorest conductor? How do you know? Question #2: Is there a small difference or large difference in the conductivity of metals and glass? Explain your answer Question #3: How can good insulators help keep the inside of a container cold when it is hot outside, but also keep the inside of the container hot when it is cold outside?

Question #4:Using the Particle Model, describe the difference between hot tea and cold tea. Question #5: For Jamie’s hot tea to ‘cool down’, what must happening to the particles that make up the hot tea? Question #6: If the tea is in the closed container, how can the particles that make up the tea transfer energy away? Question #7: If you wanted to slow down this transfer of energy, what kind of materials would you make the walls out of? Question #8: Now, for Katie’s cold tea to ‘warm up’ what must happen to the particles that make up the cold tea? Question #9: If the cold tea is in the closed container, where does this added heat energy come from, and how does it reach the tea? Question #10:If you wanted to slow down this transfer of energy into the container, what kind of materials would you use to make the walls?

Three different covered cups are placed on a tabletop. The lids are taken off of the cups, and each is filled with 250mL of hot tea (initially at 60°C). Cup 1 is made of aluminum, Cup 2 is made of glass, and Cup 3 is a white foam cup. The lids are placed back on the cups, and a thermometer probe is passed through the lid and into the tea. For 15 minutes, the temperature of the tea is measured and recorded at every 3-minute interval. The data for each cup is plotted on the graph.

 

Question #11: Look at the graph and determine what is the temperature of the room. Explain your reasoning.   

After 15 minutes, the cups are emptied, rinsed out with cold water, and refilled, this time with 250mL of iced tea (0°C). Care is taken so that no ice is placed in the cups. Only cold liquid tea is placed in the cups. The temperature of the tea in each cup is measured as it was in the first part of the experiment; every 3 minutes for 15 minutes. If the room temperature has not changed, sketch what the Temperature versus Time plots would look like for each of the 3 cups on the previous graph.  Sketch a plot for each cup, clearly labeling which graph represents which cup.

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 Question #12: Did the wax drops take the same time to melt on the hollow bar as they did on the solid bar that was made from the same material? If the answer is NO, does energy pass through the hollow bar faster or slower than it does through the solid bar (of the same material)?  Question #13: Can you explain why heat energy moves differently through the hollow bars than it did through the solid bars? 

 CONCLUSION 1. What is conduction, and why is the thermal conductivity of a substance an important property that must be considered when working with the substance? 2. What is convection, and how is it different from conduction? 3. What causes convective currents to begin in liquids and gases? 4. What was the purpose of the lab?