For every action, there's an equal and opposite reaction. The action is the chemical reaction between the vinegar and baking soda, which yields water and carbon dioxide (CO2) gas. The gas wants to escape, and giving it a little hole to escape, powers the bottle across the water (the reaction).
I did this experiment with the 3rd-5th graders in summer camp many moons ago. It wasn't exactly like this, as I don't remember the details. Luckily, there are plenty of sites out there to refresh my memory. I decided to approach it like I do cooking and looking up recipes online: a little from this recipe and a little from that recipe and add a few ingredients of my own.
- Take an old 20oz soda bottle (I used a Diet Pepsi bottle from the power vote days) - the type of drink doesn't matter, though I don't recommend water bottles now that they are more eco-friendly and very squishable (yes, that's an official scientific term).
- Dril a hole through the cap (about the size of a straw diameter).
- Place about 10 marbles in the bottle to give it weight (since the bottle is buoyant when placed in the water).
- Fill up the bottle ~1/4 with vinegar (just plain, cheap, generic name vinegar).
- Add ~1T of baking soda to the bottle (other people suggest rolling the baking soda in toilet paper. This was VERY messy and frustrating though just dumping 1T of baking soda in the bottle was relatively painless). -This is a great use for your old baking soda that A&H recommends switching out soon with the time switch. **
- Screw on the lid.
- Cover the hole in the lid and shake the bottle.
- Place the bottle in the water and watch it go!
- See if the shape of plastic bottle affects the motion (Mt Dew has a different shape than Diet Coke which has a different shape than Diet Pepsi).
- Alter the ratio of baking soda-to-vinegar and see what happens (more/less vinegar and/or baking soda).
- Race - you'd probably need a bigger tub than our small cooler.
- What made the boat move?
- What happened when I put this white powder (baking soda) into this bottle of vinegar (it's also good to ask beforehand too for a hypothesis)?
- What would happen if I try this again but differently (your choice on different, or let your child experiment)?
- What happens if we remove the marbles from the bottle?
- What did the vinegar turn into after the addition of baking soda? (water + CO2 - but the CO2 is what powered your boat)
- What else can make your boat move? (J liked using his hands)
**We've also used old baking soda down the drain and added vinegar. It magically unclogged our drain. Not as exciting to a little kid, but it saved us a trip to the store. Woohoo! Science!