We’ve done a lot of quick STEM activities. We’ve even done the leak proof bag science experiment before, although we gave it a twist as a brain surgery leak-proof bag!
But this time, we were doing a collection of pencil science experiments, so I knew we needed to add the classic quick science experiment to the list.
So, we gathered some number 2 pencils and got ready to do our leakproof bag experiment!
If you want to do this experiment at home or in the classroom, it is best suited to the outdoors, as the bag does eventually leak when you take out the pencils.
So, to avoid a huge gush of water on your floor, do it outside!
If you can’t do it outside, you can do the experiment over a large bin to catch any drips.
You may also want to check out our extensive lists of other STEM activities and science experiments for kids!
Leakproof Bag Science Experiment Lesson Plan
Want to turn the leak proof bag science experiment into a complete lesson? Just add these elements to your science time:
Experiment Variations
Any science experiment should include variations on the “right” answer. For this leak proof bag science experiment, you might try sticking other objects through the bag (like crayons or bamboo skewers) to see which one produces the least amount of leaks.
You can also test the activity with other types of materials. Does the same thing happen when you use a cloth bag? What about a different kind of plastic? Paper?
Science Explanation
Before or after doing the experiment with the kids, have a period where you discuss the science behind the lesson. This is a good resource for exploring the chemistry of polymer chains. Depending on the age of the children doing the experiment, you can explore the chemistry completely or simplify it.
I did this experiment with my kindergartner, and she was interested to learn the details of the experiment in the section below, but she was not ready for a full high-school level chemistry lesson!
Data Recording and Analysis
All good scientists know that data recording and analysis is crucial to any scientific discovery. What this looks like will depend on the grade level of the child. A young child might draw a picture of the results and write a word or two.
Older kids can write the chemical formula for polymer chains and analyze what kind of bond each type of material tested has.
No Leak Magic Bag Science Explanation
Do you know why the no leak magic bag works? It’s because of science! Plastic baggies are flexible because they contain long chains of molecules that can bend and flex. If plastic bags did not have polymer chains, the plastic would be hard and inflexible.
But, because these chains are so flexible, when you pierce the bag, the molecular chains in the plastic flex around the pencil inside the hole, creating a tight seal around the pencil and preventing the water from escaping (although you may have a few minor leaks).
When you remove the pencils, the polymer chains can’t move enough to fill the holes, so the water escapes in a fun fountain.
Supplies to Make a Leakproof Bag
You need just a few supplies for the leak proof bag science experiment, which makes it even easier to do! You’ll want to have one bag for every student and about 4 pencils per student.
You can also have your students do the activity in groups of 3-4.
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You will need:
- Quart sized plastic baggies
- Number 2 pencils (I like to use pre-sharpened pencils)
- A large plastic bin (if you’re doing the experiment indoors)
Ziploc Storage Bags, Quart, 48 Count
Pencils Pre-sharpened No. 2 144/box 12 Boxes of 12 New Improved EraserIRIS 53 Quart Stack & Pull Box, ClearThe Mason Jar Scientist: 30 Jarring STEAM-Based Projects
How to Do the Leakproof Bag Experiment
This experiment is so easy to do!
First, fill the plastic bags with water and seal them tightly.
Next, take the bags outdoors or hold them over the bin.
Ask the kids what they think will happen when you put the pencil through the bag. Many of them will think that the bag will leak right away.
Quickly pierce both sides of the bag with the pencil. If you take too long, the bag will leak.
Show the kids how the pencil has gone through the bag, but the bag isn’t leaking!
This is a good time to talk about the science behind the lesson.
Ask the kids what they think will happen after you remove the pencil.
Let the kids remove the pencils.
The water will escape right away.
Have the kids repeat the experiment with your other materials, and record their results on a science worksheet.
More Quick STEM Activities to Try
Milk Surface Tension Science Experiment