Take a Candle Carousel for a Spin

Introduction

A candle carousel spins around like an electricity-powered carousel, or merry-go-round, that you might have ridden at an amusement park. But a candle carousel is much smaller—some can fit in the palm of your hand—and it is powered by heat from candles. Figure 1 shows an example of a candle carousel. Note how the candle carousel has several tilted blades at the top, how the blades are all attached to a central shaft, and that there are candles placed below the blades. When the candles are lit, hot air rises above them, which makes the blades spin around.

Figure 1. In this science project, you will make a candle carousel similar to this one. When the candles are lit, they cause the blades at the top to spin.

Candle carousels are part of the German Christmas tradition. Known as Christmas pyramids, or candle pyramids, these German crafts traditionally depict winter or religious themes like in Figure 2. They were invented in the early 1800's; long before electrical power was in homes.

Figure 2. An example of a Christmas candle pyramid.

How does lighting the candles make the candle carousel spin? The candle's flame heats up the air above the candle. Heat is a form of energy, and it makes the air right above the candle rise above the colder air around it. This rising hot air pushes up against the blade above it. Because the blade is tilted, this push causes the blade to move sideways (to the right or left, depending on how the blade is tilted), and spin around the shaft. Each blade that moves above the flame also gets "pushed" by the hot air.

The rising hot air exerts a force on the blade, which makes it move. A force is something that pushes or pulls on something else. The force that moves the blade sideways is called lift. Normally, we think of lift as an upward force, such as with flying airplanes. However, for an airplane, air is coming toward the airplane from straight in front of it, whereas with a blade on the candle carousel, the air is going upwards, hitting the blade from below. Because lift is defined relative to which way the air is going, in a candle carousel the lift is a sideways force. Another force acting on each blade is the force of drag, which pushes upward against the blade, in the same direction as the moving air. Figure 3 shows a diagram of how the hot air and forces of lift and drag act on a candle carousel's blade to make it move. (This is very similar to a wind turbine, which you can find out more about in the project idea Unleash the Power of a Pinwheel!.)

Figure 3. This diagram shows how hot air, drag, and lift act on a blade of a candle carousel to make the blade move (rotating around the central shaft; the shaft would be directly behind the blade [the shaft is unseen in this diagram], and the blade would rotate to the left in this diagram). Note that this diagram is only showing the edge of the blade, as if the viewer is looking directly at the blade's edge.

In this science project, you will make your own candle carousel, like the one in Figure 1, and investigate how the amount of heat—generated by a varying number of lit candles—under the carousel's blades affects how fast the blades spin. You will measure the speed of the blades in rotations per minute, or rpm. Will adding more candles make the blades spin faster, or will there be no noticeable difference? What will the relationship be? Get ready to make your own candle carousel to find out!

Terms and Concepts

• Candle carousel
• Heat
• Force
• Lift
• Drag
• Wind turbine
• Rotations per minute (or rpm)

Questions

• How does lighting a candle on a candle carousel make its blades move?
• What direction is the force of lift on the blades of a candle carousel?
• Why are the blades in a candle carousel tilted?
• Why does hot air rise?

Bibliography

To find out more about the forces involved in making the candle carousel work, you can check out these resources:

• National Aeronautics and Space Administration. (NASA). (2014, June 12). Dynamics of Flight. Retrieved January 20, 2015, from http://www.grc.nasa.gov/WWW/K-12/UEET/StudentSite/dynamicsofflight.html
• Wikipedia contributors. (2015, January 5). Wind turbine. Wikipedia: The Free Encyclopedia. Retrieved January 20, 2015, from http://en.wikipedia.org/w/index.php?title=Wind_turbine&oldid=641137723
• How Stuff Works. (n.d.). How Wind Power Works. Retrieved January 23, 2015, from http://science.howstuffworks.com/environmental/green-science/wind-power.htm

Materials and Equipment

• Aluminum pie pans, 8 3/4 inch in diameter (2)
• Printer with printer paper
• Scissors
• Tape
• Ruler, metric
• Protractor
• Black permanent marker
• Plastic drinking straw
• Metal hex nut
  • It should snugly fit around the straw, and be high enough to stably stand upright with the straw in it.
  • The nut size used in this project had 1/4 inch inner diameter, 1/2 inch outer diameter, and a height of 1/4 inch.
  • We recommend that you take your straw to a hardware store and try different-sized hex nuts to make sure you find the one that fits your size straw best, since straws can vary in diameter.
• An epoxy that works well with metals and plastic, such as Elmer's® Superfast Epoxy Cement, which can be purchased from Amazon.com.
• Gloves, disposable (1 pair for each person handling the epoxy). This is for safely handling the epoxy.
• Newspaper or sheets of scratch paper. This is to protect your work space as you work with the epoxy.
• Play-Doh® (a piece approximately the size of your fist)
• A wooden skewer, at least 20 cm long, with a sharp point
• Small candles (4). They should be about 5 cm tall. A set of 12 candles that work well for this project can be purchased from Amazon.com.
• Lighter or matches
• Timer or stopwatch
• Adult helper for using epoxy and lighting candles
• Lab notebook
• Optional: Colored permanent markers for decorating the candle carousel

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Experimental Procedure

Constructing Your Candle Carousel

In this part of the science project, you will make your own candle carousel from two aluminum pie pans, a straw, a metal nut, candles, Play-Doh, a wooden skewer, and some epoxy. You will also need a pair of scissors, tape, and a printer with paper. So gather your materials and get ready to build it!

1. Take one of the aluminum pie pans and carefully cut off its tilted rim so that it now looks like a flat, aluminum circle, as shown in Figure 4.

Figure 4. Take one of the aluminum pie pans.

Figure 5. Cut the rim off of the aluminum pie pan (so you are left with a flat circle of aluminum).

2. Print out the windmill template (PDF).
3. Cut the circle out from the template and tape it to the aluminum circle with a couple pieces of tape, as shown in Figure 6. Do not use too much tape as you will be removing the paper template later.

Figure 6. Tape the cut-out windmill template to the aluminum circle.

4. Cut along the solid lines of the template and the aluminum circle below it, as shown in Figure 7.
   1. Be sure not to cut all the way to the center of the circle.

Figure 7. Cut the aluminum circle along the solid lines of the template.

5. Carefully fold the aluminum circle down along the dotted lines of the template, so that you have triangular edges pointing down, as shown in Figure 8.
   1. You can use a ruler to help make sure the lines are straight.
   2. Use a protractor to make sure the edges are bent down by about 30–40 degrees (°) compared to the top, flat strips.

Figure 8. Fold the aluminum circle down along the dotted lines.

6. Gently remove the paper template from the aluminum circle, which should now look like an aluminum windmill, as shown in Figure 9. You will need to remove the paper template for your candle carousel to work.

Figure 9. Gently remove the paper template from the aluminum windmill.

7. Optional: At this point (or at a later point), you can decorate the blades of the windmill (using colored permanent markers) if you would like to. Figure 10 shows one example of some decorated blades.

Figure 10. Decorated windmill blades.

8. Flip the windmill over so that the triangular edges are pointing up. In the center of the windmill, make a small dot using a permanent marker, as shown in Figure 11.
   1. You should use a ruler to find the center by measuring along the length of each flat strip and calculating where the center of each of the strips is; where they all intersect is the center.

Figure 11. Use a permanent marker to make a dot in the center of the windmill, on its underside.

9. Cut a straw to make a straight piece that is 5 centimeters (cm) long. Make sure the straw piece fits snugly in the metal hex nut you have.
10. Have an adult help you use epoxy to attach the nut and straw piece onto the dot you made on the aluminum windmill. Be sure to follow all proper safety precautions (should as wearing disposable gloves) when using the epoxy. The nut should help hold the straw piece straight up (vertically). When it is attached, your windmill should look like the one in Figures 12 and 13.
    1. Read all safety warnings on the packaging before using the epoxy. Be sure to wear gloves when handling the epoxy.
    2. To do this step, make a spot of epoxy on a disposable surface, such as sheets of newspaper, dip the nut (with the tip of the straw snugly inside) onto the spot of epoxy, and then quickly place the nut onto the dot you made on the windmill.
       1. Make sure you can see the dot when looking down through the straw; it should be centered on the dot.
       2. Get as little epoxy on the dot that you drew as possible, as this could later interfere with the ability of the windmill to smoothly spin on the skewer.
    3. Note: It is important to make sure that the straw is as vertical as possible. If the straw is not pointing straight up, the candle carousel blades will not work well. Look straight down at the straw (from the top), and from all sides, to make sure it is pointing up straight. While the epoxy is still fluid, you can gently adjust the direction in which the straw is pointing.
    4. Let the epoxy completely cure (which may take 24 hours) before testing the windmill; in the meantime, you can continue on to step 10.

Figure 12. Side view of the straw (inside the nut) and nut being attached to the windmill.

Figure 13. Top view of the straw (inside the nut) and nut being attached to the windmill.

11. While the epoxy is curing, you can make the candle carousel's stand. This will be made using the other aluminum pie pan. Take the other aluminum pie pan and use a permanent marker to make a dot in the center. Then make four dots around the edge of the pan that are all equally spaced apart, and an "X" next to each dot, as shown in Figure 14. (You will later be placing a candle on each "X.") Note: Be sure you use a ruler to measure and make all of the dots.

Figure 14. On the second aluminum pie pan, make a dot in the center, and four dots (with an "X" next to each) equally spaced along the edges.

12. Next, cut (or break) a wooden skewer so that it is 20 cm long (and still has one pointed end). Then take a small fist-sized piece of Play-Doh and stick the flat end of the skewer into it. Place the Play-Doh and skewer onto the center dot of the aluminum pie pan. Be sure the skewer is right on the dot. Press down on the edges of the Play-Doh ball to flatten it onto the pie pan a little so that it looks like Figure 15.

Figure 15. Place the wooden skewer into a piece of Play-Doh, and stick that onto the center of the aluminum pie pan.

13. Make sure that the skewer is as vertical as possible in the Play-Doh on the pan. (For the candle carousel to work well, the skewer needs to be as straight as possible.) Let the Play-Doh harden a bit by letting the candle carousel's stand sit out for at least a few hours.
14. When the windmill's epoxy has cured, and the Play-Doh has hardened, you can try out your candle carousel! Place the windmill's straw onto the top of the skewer. Also place one candle on each "X" on the carousel's stand. Your setup should now look like Figure 16.

Figure 16. Place the straw's windmill onto the pointed tip of the wooden skewer, and a candle on each of the four dots around the stand's edge, and your candle carousel is ready to try out!

15. Try out your carousel to make sure it works! To do this, set it up on a flat, stable surface (such as a table or desk) that is not near any source of air movement. For example, set it up in a room with closed doors and windows, and away from any active air vents. Even a gentle breeze can completely disrupt the candle carousel's movement.
16. Now have an adult help you light all four candles. Watch to see if the candle carousel's blades (the windmill part, on top) start to spin. You may need to wait for a minute before you see any movement. Once it is working, you can move on to the next section, "Testing Your Candle Carousel." If the blades do not spin after waiting for 2–3 minutes (min), try to troubleshoot by checking the following:
    1. Make sure the candle flames are completely upright and are not flickering or moving sideways. If they are flickering or moving sideways, there may be air movement that is disrupting them. The flames need to be completely upright for the candle carousel to work well; if the flames are not upright, the hot air will not be moving directly upward to the blades.
    2. Make sure the windmill part is sitting horizontally on the skewer (and parallel to the carousel's stand). If the windmill is tilted on the skewer, the straw may be rubbing the skewer (creating friction) and preventing the blades from spinning.
    3. See if there are any other possible sources of friction that could be slowing down the blades' spinning. To do this, look at where the skewer and straw meet. The skewer should ideally only touch the aluminum on the windmill where you drew the dot (within the nut).
    4. Make sure the blades are all at a 30° angle, and that the straight strips on the windmill are still straight and horizontal (and parallel to the carousel's stand).
    5. You could try making the skewer shorter, as this will decrease the distance that the hot air has to travel from the flames. If you do this, blow out the candles, remove the windmill part from the skewer, and try to carefully pull the skewer straight out of the Play-Doh. When you make the skewer shorter, make sure the windmill's blades will still be at least about 5 cm above the flames of the lit candles. Stick the shortened skewer straight back into the Play-Doh hole and try the candle carousel again.

Testing Your Candle Carousel

In this part of the science project, you will investigate how the amount of heat (the number of lit candles) under the carousel's blades affect how fast the blades spin. You will measure the speed of the blades in rotations per minute (or rpm).

1. In your lab notebook, make a data table like Table 1. You will be recording your results in this data table.

	Rotations per Minute (rpm)
Number of Lit Candles	Trial 1	Trial 2	Trial 3	Trial 4	Trial 5	Average
1
2
3
4

Table 1. Make a data table like this one in your lab notebook in which to record your results.

2. Make a mark (like a small line) on the edge of one of the carousel's blades. It should be visible enough so that you can easily see it while the blades are spinning around.
3. Have an adult help you light one of the candles.
4. Wait for 3 min.
   1. Waiting will let the heat from the flame build up and ensures that the blades are moving at a constant speed when you start taking your measurements.
5. Now count how many rotations the blades make in 30 seconds (sec).
   1. To do this, watch the mark you made (in step 2) and orient yourself so that you can see when it goes directly above one of the candles. Then count how many times the marked blade spins above that candle in 30 sec.
   2. If the blades are not spinning at all, record "0" for the rpm in the data table for this number of lit candles.
6. Multiply the number of blade rotations in 30 sec by 2 to give you your results in rpm (the number of rotations in one minute, or 60 sec). Record your answer in your data table.
7. Repeat steps 5–6 four more times so that you have done a total of five trials for this number of lit candles.
   1. Make sure that none of the testing conditions change while you perform your different trials. For example, do not move the candle carousel, and make sure the candle flame(s) remain straight and upright the entire time.
8. Repeat steps 3–7 three more times so that you have tested the candle carousel with one, two, three, or four candles lit.
   1. When you light the second candle, light the one that is at the opposite side from the first candle (so that the lighting is symmetrical). For the third candle, it does not matter which candle you light.
9. Calculate the average number of rpm's for each number of lit candles. Record your results in your data table.
   1. To calculate the average, add up the numbers for each trial and then divide by the number of trials. For example, if when you had two candles lit, the blades spun at 32 rpm, 30 rpm, 31 rpm, 30 rpm, and 31 rpm for the five trials, the average rpm for two lit candles would be 31 rpm (since 32 + 30 + 31 + 30 + 31 = 154, and 154 ÷ 5 = 31).
10. Make a line graph of your data, plotting the average rpm versus the number of candles.
    1. Place the number of candles on the x-axis (the horizontal axis) and the rpm of the blades on the y-axis (the vertical axis).
11. Analyze your results. Look at your data and graph and try to draw some conclusions.
    1. How does lighting more candles appear to affect how fast the candle carousel's blades spin?
    2. Can you explain your results in terms of how the heat from the candles' flames makes the blades spin?
    3. For a more-advanced challenge, see if you can figure out whether the relationship between the number of lit candles and the speed at which the blades are spinning is a linear relationship or if it is non-linear.
       1. If it is a linear relationship, the data points should make a straight line (or a nearly straight line).
       2. Why do you think you see the relationship that you do? What does this tell you about how increasing the amount of heat under the blades affects the blades' rotational speed?