H2-Oh My! A holey bottle that will not leak!

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If you want to play a little practical joke on someone, I may just have the thing for you.

This experiment involves piercing small holes in a bottle of water. If we open the cap and allow air to enter the bottle, water will flow freely out of the tiny holes thanks to pressure and gravity. If the cap stays on, air cannot enter the bottle and the water will stay put!

Caution: you (or they) might get wet!



How to make the H2-Oh My holey bottle experiment

Supplies you will need

For this experiment, you’ll need:

  • A full plastic water bottle
  • Thumbtacks or sewing needle
  • Optional: marker

Before you start

Watch little fingers around the thumbtacks.

Also, the person holding the water bottle may get wet!

Instructions

Here is how to do this experiment with your child:

Step 1: Be sure your water bottle is full with the cap ON

The first step is to fill up your plastic water bottle (if it isn’t already) and ensure that the bottle cap is on tight.

Step 2: Poke holes in the bottle

Use your thumbtack to poke a few small holes about an inch or two above the bottom of the bottle.

A little bit of water may drip out, but it won’t be much. Just use a towel to wipe up anything that has spilled.

Step 3 (optional): Label your bottle

If you want to get super playful with this experiment, use your marker to write “DO NOT OPEN” on the side of the bottle.

Step 4: Unscrew the cap and get soaked!

Unscrew the cap and the water will start bursting out of the tiny holes you created in step 2.

Be careful: you might get wet!

The STEM behind the H2-Oh My holey bottle experiment

This experiment teaches:

  • Pressure and flow
  • Observation skills
  • Surface tension

How it works

When you pour liquid out of a bottle, it’s replaced by air. Try emptying the bottle by turning it upside down. Do you see those large bubbles float from the bottle opening and up the liquid? That’s air rushing in!

If the hole from which the liquid drains is too small to let air rush into the bottle, then the water won’t leave the bottle.

When you open the cap to the bottle, air rushes in and the water can freely flow out of the tiny holes, thanks to gravity and some pressure from the air.

Pressure and flow

This experiment can help kids understand the concept of pressure.

Before the bottle cap is removed, there is a pressure balance between the inside and outside of the water bottle. As long as the cap is on, this balance in pressure prevents the water from flowing out of the holes.

We disrupt that pressure balance when we take the bottle cap off of the bottle.

By removing the bottle cap, we allow air pressure to enter the water bottle, which allows the water to flow freely out of the holes.

If you screw the cap back on the bottle, the flow stops again!

Observation skills

It’s important to really observe what is going on here, since this experiment can become a fun trick and nothing more to a kid.

Take the time to really observe what is going on with your child. When you poke the holes in the bottle, have your child watch closely to see if any water comes out (a tiny bit will).

Ask your child to hold the bottle and give it a gentle squeeze. Does that cause water to come out? Why does it? (This happens because there is a small pocket of air at the top of the bottle and you are helping it apply force to the water.)

What happens if we unscrew the cap only a little? How does that differ from completely unscrewing the cap?

Taking the time to observe what is happening in each step of this experiment helps kids build on their observation skills, which can be crucial for future learning!

Surface tension

Observing how water forms small droplets around the holes (if they’re tiny enough) can introduce the concept of surface tension, a property of water that allows it to resist breaking apart.

Imagine the water inside the bottle as a big blob wanting to minimize its surface area due to surface tension. This “minimization” pulls inwards on the water at the edges of the holes, creating a slight inward pressure.

While it’s small, this inward pressure from surface tension slightly opposes the outward pressure exerted by the water pushing downwards due to gravity. This resistance helps contain the water within the bottle temporarily.



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