The leak-proof bag experiment is a fun science experiment in which your kids get to poke pencils right through a plastic baggy filled with water.
Amazingly, the water doesn’t come pouring out!
This is a quick and easy experiment to set up too.
Grab a sealable bag, any size will work. We used a quart sized baggy. Fill it up with water and close up tightly.
Then stick sharpened pencils through it!
Yep, that’s right it doesn’t leak!
I thought I was going to need super sharp pencils, but that wasn’t the case. The pencils went through with ease.
One person needs to hold the bag of water while your child pokes the pencils through.
It’s pretty cool! And my kids were amazed! We did it over and over again.
One side note, the bag will leak if you start poking a pencil through and remove it. If that’s the case, stick the pencil into the hole and continue through to the other side.
You’ll see in the video below we had a slight leak because of that.
The science behind the Leak-Proof Bag Experiment
This idea came from a science teacher, Curt Nelson of MakeAKidnection.com, who shared the experiment with the details of why the bag doesn’t leak.
Leak-Proof Bag Experiment Supplies:
- A plastic baggy (I use quart-size, but sandwich size will also work)
- A few sharpened pencils to poke through the bag
- A permanent marker to draw faces on the bag
- Water to fill the bag about 2/3 full
Then prepare the bag as shown in the video below.
The Added Fun
To spice the experiment up, we’re going to pretend that germs have invaded our water supply. Your kids will come to the rescue and help us exterminate those pesky germs.
And to make sure your kids get into the spirit, Bob the Dragon and I shot a short video to set the stage.
Watch the middle portion of this video with your kids:
The Science Behind the Leak-Proof Bag
Why doesn’t the water leak out of the bag? It’s because plastic bags are made of polymers, or long chains of molecules. The pencil squeezes between two chains, increasing the gap between them at the point, but it doesn’t break the chains.
Watch this part of the video to see how many pencils I was able to poke through one bag — it’s really an amazing example of polymer science.
Latex balloons are also made of polymers, which means you can poke a skewer right through a balloon without popping it (if you know the secret). If you want to blow your kids’ minds, follow this link to get my super-simple explanation of this fun magic trick / science demo. Your kids will love it!
More experiments like the leak-proof bag experiment:
Curt Nelson is a former science teacher and school assembly presenter. Now he (and Bob the Dragon) use stories to make learning science fun at MakeAKidnection.com. Follow along with him on YouTube and Facebook.