Science experiment: “Sewer Bugs”
It’s raining. It’s pouring. It’s time to find an activity to do to entertain the kids indoors.
A classic demonstration that many science teachers do to grab students’ attention is to put raisins into a glass of carbonated soda. Usually Mountain Dew is used because of the fluorescent yellow color. The raisins float up and down, and from a distance, they appear to be water bugs. The teacher may start the lesson, holding up the glass, telling an embellished and fabricated story about the bugs origins, where they were collected, etc. Then the teacher takes a big swig of the drink, and of course, the shrieks of horror from the students ensue. (My apologies to all my fellow teachers for having given away this magic trick.)
I have modified this demonstration to teach science observation, critical thinking, and deductive logic. This activity also meets the following areas of Texas TEKS preschool guidelines: encourages language skills (listening comprehension, sentence structure, vocabulary), mathematics (counting, measurement)
- 2 clear drinking glass
- 20 raisins
- carbonated drink (preferably a clear soda, sparkling or seltzer water)
- measuring cups
- paper & pencil
- Have the child count out 20 raisins.
- Divide the raisins into two equal groups of 10. Have the child count 10 raisins as he/she piles the raisins.
- Have the child measure 2 cups of carbonated drink, and pour that into one clear glass.
- Have the child measure 2 cups of water, and pour that into the other clear glass.
- Have the child make observations about the two glasses. (Ask questions such as what do you notice about the carbonated glass that you don’t see in the clear water glass. What do you think will happen when we put the raisins into the glass with the bubbles? What will happen when we put the raising into the glass without the bubbles.)
- Drop 1 raisin at a time into the WATER glass. Again, ask the child questions about what he/she observes. Ask again what the child thinks will happen when the raisins are dropped into the carbonated drink glass.
- Drop 1 raisin at a time into the CARBONATED drink glass. Again, ask the child questions about what he/she observes. Ask again what the child thinks will happen when more raisins are dropped into the carbonated drink glass.
- If the child is capable of illustrating, have the child draw what he/she observed.
- Followup: Ask the child if he/she thinks that a similar effect will take place if you drop a smaller, raisin sized object like peas into the liquids. Repeat experiment.
Explanation: The raisins in the carbonated drink will sink all the way to the bottom of the soda because raisins are more dense than the soda. The gas bubbles from the carbonation pushes the raisins up to the surface, but once the CO2 gas bubbles release into the air, the raisins sink back down to the bottom of the glass.
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