Make a Tiny Diver Sink with One Squeeze

Try this with a clear plastic bottle, water, and a small eyedropper. Fill the bottle to the top, place the partly filled eyedropper inside, cap it tightly, and squeeze the sides. The tiny diver sinks. Release the bottle, and the diver rises again. 12

The squeeze raises the water pressure. Water moves into the eyedropper and compresses the trapped air, so the diver becomes denser and sinks. Releasing the bottle lets the air expand, bringing the diver back up. 12