Diving Rainbows in 5 Steps

Materials you'll need

• Flexible (bendy) straws
• Colorful paper clips
• Scissors
• A glass of water (for testing)
• A large clear plastic bottle with a cap (2-liter works great)
• More water

 

Step-by-step tutorial

Step 1: Cut the flexible bendy section off of a straw. Fold it into a U-shape so the two ends meet, then clip a paper clip around the two ends to hold them together.

Step 2: Drop your diver into a glass of water. It should just barely float near the surface. If it sinks, remove a paper clip; if it floats too high, add one. Make as many divers as you like — one for each color of your rainbow!

Step 3: Fill your large plastic bottle all the way to the top with water.

Step 4: Drop all your divers into the bottle, then screw the cap on tightly so no air can escape.

Step 5: Squeeze the sides of the bottle hard and watch the divers dive to the bottom. Let go, and they float back up. Try controlling which ones dive and which ones stay up.

Learn more

This experiment is a classic called a Cartesian diver. When you squeeze the bottle, you increase the pressure of the water inside. That pressure pushes into the tiny air bubble trapped in your straw diver, compressing it — making the diver denser than the surrounding water, so it sinks. When you let go, the pressure drops, the air bubble expands back to its original size, and up the diver floats again. It's the same science that helps submarines dive deep and rise back to the surface.