The "Broken" Straw

A Science in the Park experiment from Hayward Education Foundation. Put a straw in water and it looks snapped in two! Find out how water plays tricks on your eyes.

Welcome to the "Broken" Straw Experiment!

Can water break a straw?

Try this quick experiment and see for yourself!

Watch the video, then follow the steps below. Put a straw in a glass of water and look from the side. The straw looks bent or even snapped in two! It's all thanks to refraction, the bending of light.

What You’ll Need:

A clear drinking glass
Water
A straw or a pencil
For the bonus: a small piece of paper and a pen

How to "Break" the Straw:

Fill the glass:
Pour water into the glass until it is about half full.
Add the straw:
Put the straw in the glass and let it lean against the side at a slant.
Look from the side:
Get down so your eyes are level with the water. Where the straw goes into the water, it looks bent, shifted, or even snapped in two!
Now look from the top:
Look straight down into the glass. Does the straw still look broken? Pull it out to check. It was never broken at all!

How It Works: The Science Behind the Trick!

Light travels in straight lines, but it slows down when it moves from air into water. When light changes speed like this, it bends. Scientists call this refraction.

The part of the straw above the water sends light straight to your eyes. But light from the part underwater bends as it leaves the water. Your brain doesn't know the light bent. It assumes light always travels in a straight line, so it sees the underwater part of the straw in the wrong place. The two parts don't line up, and the straw looks broken!

Why does it look fine from the top?
When you look straight down, the light comes up out of the water head-on, so it hardly bends at all. Light bends the most when it hits the water's surface at a slant.

Key Takeaway: Don't Always Trust Your Eyes!

Your brain expects light to travel in straight lines, so bent light can fool it. That matters in real life:

Fishing: A fish is not exactly where it looks like it is! Birds like herons learn to aim a little lower to catch their dinner.
Swimming: Pools look shallower than they really are, so always check the depth sign before you jump in.
Lenses: Eyeglasses, cameras, and microscopes all bend light on purpose to help us see.

Scientists use careful tests, not just their eyes, to find out what's really true!

Bonus Experiment: Secret Message Magnifier!

Water can do more than bend a straw. It can also make things look bigger! Try this:

Write it tiny: Write a secret message on a small piece of paper in the tiniest letters you can.
Hide it behind the glass: Hold the paper right behind a round glass of water.
Look through the water: The curved water works like a magnifying glass and makes your message look bigger and easier to read.
Move it around: Slowly slide the paper farther back. Watch what happens to the letters. They may even flip backwards!

Bonus Learning: Bending Light in Everyday Life

Rainbows: Light bends and bounces inside raindrops, splitting into all its colors.
Swimming pools: Look up from underwater and the surface can look like a shiny mirror. That's total internal reflection too!
Aquariums: Look at a fish tank from the corner and you may see the fish reflected, or not see them at all!

Tips for the Best Results:

Use a clear glass: A plain glass with smooth sides gives the clearest view.
Tilt the straw: A straw standing straight up won't look as broken. Let it lean at a slant.
Get down to eye level: Look right at the water line from the side for the biggest break.
Use a bright straw: A colorful straw or pencil is much easier to see through the water.

Wrapping It Up: Magic or Science?

It may look like the straw snapped, but now you know the secret: light bends as it leaves the water, and your brain gets fooled. The straw was in one piece the whole time!
Ready for more? Head back to Science in the Park and try the Reversing Arrow and the Disappearing Coin experiments next!