Start the leak proof bag experiment by asking kids a simple question: What happens when you poke a water-filled plastic bag with a sharp stick or pencil? They’ll probably say there’s going to be a hole in the bag, and the water’s going to leak out of the bag. Do the experiment and prove them wrong.
Safety reminder: Supervise the kids as they handle the sharp pencils or sticks they need for this experiment.
STEM concept: Molecules, polymers
Materials for Leak proof bag experiment
• ziplock bags
• objects with sharp ends (pencils, bamboo skewers, etc.)
Steps to follow
1. Fill the ziplock bag with water and close it up tightly.
2. Stick the sharp ends of the pencils or bamboo skewers through the bag.
3. Make sure the pencils or skewers go through to the other side.
4. Watch what happens.
5. Pull out the pencils or skewers from the bag and see what happens.
The science behind the experiment
Plastic bags are made of polymers. Polymers are long strands or chains of molecules that are highly flexible. When the sharp objects go through the plastic bag, they push through the polymer chains, but don’t break them. Instead, the chains or strands of molecules stretch to make room for the pencil or skewer and re-seal themselves around the sharp object. This prevents water from leaking out of the bag.
When you pull out the pencil or skewers from the bag, the molecules cannot cover the big hole left behind. This causes water to leak out of the bag.