Raisins are heavier than water, so they sink when you drop them into a glass of soda water. Then something changes. Carbon dioxide — the gas that makes soda fizzy — collects on the bumpy surface of each raisin. Tiny bubbles cling to the wrinkles and ridges, and once enough gather, that upward push becomes strong enough to carry the raisin to the surface. At the top, the bubbles pop and release their gas. Without them, the raisin sinks again and the cycle repeats.

Spaghetti is denser than water, so it normally sinks. Adding baking soda and vinegar to the water changes things. The two ingredients react to produce carbon dioxide gas, and those bubbles stick to the spaghetti. Once enough collect, the upward push from the water — helped along by the bubbles — lifts the spaghetti to the surface. When the bubbles pop at the top, the spaghetti sinks again and the cycle starts over.

When you drop raisins into a fizzy mix of vinegar and baking soda, they sink at first. Then tiny gas bubbles form on their wrinkled surface. As those bubbles collect, they carry each raisin upward. At the top, the bubbles pop and the raisin sinks again. The cycle repeats as long as the mixture keeps producing bubbles. All you need is a glass jar, vinegar, baking soda, tap water, and a handful of raisins.

Water is normally denser than oil and sinks to the bottom — but gas bubbles can change that. In this project, you pour oil over colored water in a clear bottle, then drop in an Alka-Seltzer tablet. The tablet reacts with water and releases carbon dioxide gas. That gas attaches to drops of colored water, making each drop lighter. The drop floats up through the oil. At the surface, the gas escapes and the blob sinks back down. The rising and sinking cycle repeats until the tablet dissolves completely.