Magic Candle Seesaw - Sick Science!

Recently, the scientists at Spangler Labs had a day where they recollected their fond memories of elementary school. Some thought back to their favorite science or math class, but Steve was excited about the playground equipment. He loved the monkey bars, the swings, and even loved to play tetherball.

But, he recalled, his favorite thing to do on the playground was seesaw. Steve's memories even included a daredevil stunt where he seesawed while the seesaw was on fire.  He was a regular elementary Evil Knievel. Looking back on his seesaw expertise, it hit him...what if he could use some amazing science principles to make a magic seesaw?

Materials

• Pointed-tip scissors
• 2 small birthday candles
• 3 paper clips
• Ruler
• 2 oz plastic cup
• Thumbtack
• 2 straws
• Matches or lighter
• Newspaper or surface you don't mind getting wax on

1. Using the pointed end of the scissors, poke a hole into the bottom of the 2 ounce plastic cup. The hole should be just big enough to slide in the end of one of the straws.
2. When you have the hole in the cup, slide the end of a straw in so that it is sturdy and able to stand.
3. Using the ruler, find the middle of the remaining straw. Once you have found the middle of the straw, poke a hole through it using the thumbtack. Try to keep the thumbtack level as you poke through the straw.
4. Take one of the paper clips and straighten out the smaller loop so that it is almost straight. Take the end of the straightened side and bend it upwards. The shape you end up with should look like an "L" connected with a "J."
5. Slide the "L" end of the paperclip you just bent through the straw where you punched the holes. Slide the paperclip so that the straw is at the bottom of the "L."
6. Now take the "J" side of the bent paper clip and put it into the top of the straw opposite the cup. Your apparatus should look like a seesaw now.
7. Insert the flat "wickless" end of the candles into the two ends of the seesaw straw. To keep the candles in place, paperclip the outside of the straw.
8. Balance the seesaw by sliding the two candles in or out of the straw.
9. Now that you're balanced, set your apparatus on a surface that you don't mind getting candle wax on, light both of the candles, and watch the magic happen.

How does it work?

The Magic Candle Seesaw is actually based on the physics of Sir Isaac Newton's Third Law. The law states that for every action, there is an equal and opposite reaction. For example, this law of physics makes jet flight possible. The propulsion from the back of a jet makes the jet itself move forward. The initial action is the jet propulsion, the equal and opposite reaction is the movement of the jet.

So what makes this law apply to the Magic Candle Seesaw? It's actually much simpler and on a much smaller scale than the jet example above. If you carefully watch the end of the seesaw that is closer to the ground, you'll notice a drop of wax fall. Believe it or not, this one drop of wax falling is the action that creates an equal and opposite reaction of the seesaw's upward motion. Amazing, right?

Click the thumbnail below to see the video.

• Candle Seesaw
February 9th, 2011

 it 's cool Jane Taylor for Sam and Phoebe    -  February 12, 2011 This user gave 4/5 stars It was cool because the candles went up and down,up and down. They smoked down and I think the smoke pushed the candle up. The wax dripped and the smoke came out. Sam, age 7 and Phoebe, 5. Nice one mammy    -  February 11, 2011 This user gave 4/5 stars I think as one candle burns, the air above it get hot and rise up reducing the air pressure above it. The pressure difference above and below the candle forces a colder air (contains more oxygen) from underneath the candle to push it up causing the candle to burn faster. At the same time, the other candle is in its lower position where the flam is directly touching the wax causing it to melt fast and losses weight, his loss of weight making the candle to rise up. What you think Spangler? Mammy Seasaw jacqueline earls    -  February 10, 2011 This user gave 5/5 stars I think the weight of the melted wax pulls the candle down, and then the causes it to rise again. Chnage of weight? cdmiller    -  February 10, 2011 This user gave 3/5 stars Isn't the system essentially a balance? So when one candle drips wax it weighs less causing the balance arm to fall on the heavier side? Jet propelled seesaw? Terry Harvey-Chadwick    -  February 10, 2011 This user gave 3/5 stars When I watched the video for this experiment, it seemed to me that it was all about the changing mass of the candles. As one candle burns more than the other the wax melts quicker, so it becomes lighter, so the other candle moves down. When the other candle is down, the flame is able to melt the wax more quickly, so it loses mass more rapidly. The other candle, at the top of the seesaw, melts more slowly, as the flame is now pointing away from the candle, so it doesn't lose as much mass. As the masses change, the forces become unbalanced, and the seesaw moves, reversing the positions. I'm sure there is some reaction force from the melting wax as it drops, but this would be minimal, surely? Love it! Cris Sheffel    -  February 9, 2011 This user gave 5/5 stars This video put the biggest smile on my face, after which I went scrambling for straws, birthday candles, and a paper clip. Alas, no birthday candles in the house! I'll have to wait until tomorrow. :( My high school physics students are gonna love this demo when we talk about center of mass! BTW, the music is a perfect compliment to the demo. Thanks!

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