July 4th Magic Straws

Materials you'll need

• Clear glasses
• Water
• Red and blue food coloring
• Bendy (flexible) straws
• A tray (optional — to catch drips!)

 

Step-by-step tutorial

Step 1: Set up your three glasses on a tray and pour water into one of them. Add a few drops of red food coloring to one glass and blue to another, leaving the middle glass clear.

Step 2: Hold a bendy straw in a glass of water so the whole straw is submerged. Then place one finger firmly over each end of the straw to plug it — keeping the water trapped inside.

Step 3: With your fingers still plugging both ends, lift the straw out of the water and position the bent part over the rim between two of your glasses, with one end dipping into each glass.

Step 4: Release your fingers at the same time and watch the water flow from one glass into the other.

Learn more

The secret to this trick is air pressure — the invisible force of the air around us pushing on everything. When you plug both ends of a full straw with your fingers, there's no air left inside to push down on the water, so the air pressure pushing up from below holds the water in place against gravity. The moment you release your fingers and dip the ends into your glasses, air rushes in and the water flows — moving from the fuller side to the emptier one until the levels even out.