Water pushes up on everything inside it — that upward push is buoyancy. Drop a raisin into soda water and it sinks at first. Then carbon dioxide bubbles begin collecting on its bumpy, wrinkled surface. As enough bubbles gather on the ridges, the combined upward push on the raisin and its bubbles becomes strong enough to lift them to the surface. When the bubbles pop and release their gas, the push can no longer hold the raisin up, and it sinks again to repeat the cycle.

Water constantly pushes up on objects placed in it. That upward push is buoyancy. Spaghetti sinks because the water's upward push alone is not strong enough to hold it up. When carbon dioxide bubbles from baking soda and vinegar stick to the spaghetti, the water now pushes up on the combined bundle of spaghetti and bubbles. That combined push is enough to move them to the surface. Once the bubbles pop, only the spaghetti remains, and the water's push is too weak again.

Water pushes up on anything placed in it, and that push is buoyancy. Drop raisins into a fizzy mix of vinegar and baking soda and they sink at first. Then tiny gas bubbles form on their wrinkled surface. The water's upward push now acts on the raisin and its bubbles together, and that combined push carries them up. At the top, the bubbles pop and the raisin sinks again. As long as the mixture keeps producing bubbles, the cycle repeats — raisins rising and falling on their own.