Array Leak-Proof Bag STEM Experiment | Montessori From The Heart
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Leak-Proof Bag STEM Experiment


Leak-Proof Bag Pencil Arrows is a fun kids science experiment for preschoolers and kindergarteners to explore STEM education and properties of a polymer.

Can you poke a hole in a bag of water and prevent the water from coming out? Well, after learning the science behind this pencil arrows experiment, you will be ready to poke holes in a bag full of water while holding it over someone’s head! Besides, this Leak-Proof Bag STEM Experiment will take you less than five minutes to set using items around the house. Most importantly, your child will witness how a polymer reacts to holes being pressed through it without having to go to a science lab!


WHAT you will need for this Leak-Proof Bag STEM Experiment:

  • a zip-lock bag
  • sharpened pencils
  • water

HOW to conduct this Pencil Arrows STEM Experiment:

First, fill the zip-lock bag about 2/3 full of water. Next, squeeze out the air, and zip it closed. Thereafter, hold the bag up and, using the sharp end of one pencil, carefully poke the pencil through the bag until it pierces both sides, but not all the way. Make sure though that the pencil goes in on one side and comes out the other side. Ask your child, how much water would leak out?


Observe: The pencil went in one side and out the other without spilling a drop!

Science mystery behind this Leak-Proof Bag STEM Experiment:

Most plastic bags are made from low-density polyethylene. Polyethylene is a plastic polymer which is durable, long, flexible chains of molecules. So, when you poke a pencil through the bag into the polymer, the pencil slides between the molecules. Those molecules stretch and spread apart, thereafter sealing themselves around the pencil as they return to their original unstretched position. Thus, the polyethylene molecules separate but do not break! As such, the tip of the pencil squeezes between the chains and chains’ flexible property helps to form a temporary seal against the edge of the pencil. This seal prevents the water from leaking through the holes! 


Do this activity outside or over a sink or a waterproof tray as the water will pour out when the pencil is removed or pushed all the way! Also, if the pencil is pierced into the bag before the water is put in, the water will leak! Because polymers cannot seal themselves back together, due to the large opening, the water will pour out and the bag will leak! Find more cool experiment in a book The 101 Coolest Simple Science Experiments.

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Try this STEM experiment with a faceted pencil, a larger pencil, or a thicker pencil. What happens?

Want more?

For more STEM experiments, see HERE Magic Milk Experiment. Also, see HERE Magic Balloon Experiment your kids would love!

Please, always supervise your children.

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1 Comment

  • Reply Upside-Down Water Glass Trick | Montessori From The Heart September 9, 2019 at 1:02 pm

    […] you liked this STEM Kids Science Experiment, see HERE Leak-Proof Bag experiment. Also, see HERE Dancing Corn-Raisin trick. Lastly, see HERE Fizzing […]


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