Supplies needed for a simple science project include safety goggles, a plastic film canister with snap-on lid, water and a few Alka-Seltzer tablets broken into different size pieces. A stopwatch, pen and notepad are useful for writing down results.Use a clear canister if possible; the lid should be secure, but not impossibly tight. This will be messy, so you may want to conduct this experiment outdoors.
Fill the canister about 1/4 full of water. Break the Alka-Seltzer tablet into four equal pieces. Put one piece of the Alka-Seltzer tablet into the canister, quickly give it a good shake and then set it down on a flat surface to see what happens. As long as the lid isn't too tight, it will quickly pop off the canister. Try using different amounts of liquid and varying size pieces of Alka-Seltzer tablets. Write down the results to see which combination results in the biggest pop. Try putting the canister upside down on the flat surface and watch what happens.
Take the previous project a step further by adding a few more supplies. Take a cardboard tube, such as an empty paper-towel tube, and seal one end off using duct tape. Break an Alka-Seltzer tablet into four pieces. Fill the canister half full of water and drop one piece of tablet into the canister. Put the lid back on and drop the canister lid-first into the sealed cardboard tube. Point the tube away from yourself and watch what happens. The canister will fly out of the tube.
Invite a few more children to have fun with science. Be sure to provide safety goggles for each child participating. Draw a chalk line outside on the pavement or similar and let the kids see whose bottle rocket can go the furthest. Discuss the results and ask the kids if they know why the Alka-Seltzer tablets make the canisters fly out of the tubes. The answer is that carbon dioxide created from the Alka-Seltzer tablet causes pressure inside the canister to increase, eventually forcing it to fly open.