Science of Technology

From DMontalvo:

• If you invert a beaker over a candle flame, it will eventually go out as the O2 is used up and CO2 fills up the space.
• Since beakers have their volume marked on them, you can measure the time for each volume of air to be “used up.”
• We used tea lights and four different beakers: 50 mL, 150 mL, 250 mL and 400 mL. The 50 mL takes around 2 sec and the 400 mL takes around 16 seconds. The only issue was re-lighting the candles between tries. I let my kids re-light them with a wood splint lit from a second candle, but I have a small honors class. Probably the teacher should be re-lighting the candle.
• Before doing the experiment, they should make general observations about how a candle goes out (turn off the room lights) - they should notice that the last thing they'll see is a faint blue glow. This makes a good companion activity to Pete's observation of a candle flame activity.
• Once they have the data, they can graph it - ours came out roughly linear. This is a good opportunity to teach the idea of line of best fit.
• Then they can use their line of best fit to predict the time for a 100 mL beaker (interpolation) and a 600 mL beaker (extrapolation). Then you can gather all the predictions on your smart board and you can do both of them with the class watching to see how close everyone is. Prizes for those within a certain number of seconds from the actual might be a cool thing here.
• Then you can have them try to predict the time for a 1000 mL beaker. Since I stopped the graph at 600 mL, another method is needed. They can divide each trial to get a mL/sec rate of using up the air. Then they can use the average rate to make their prediction. Those teachers who are more ambitious could even have them use the slope of the graph. My numbers came out to be between 20 mL/sec and 25 mL/sec.
• Important note - when they put the beaker over the candle, they should not approach from the top. If they do that, the beaker will fill with CO2 on the way down. They should start with the beaker beside the flame and invert the beaker over it in one smooth motion.