Cool Pencil Trick with a Plastic Bag and Water
Are you looking for a fun easy to do science experiment? This fun science trick uses simple materials that you probably already have around your home or classroom. Everyone loves this cool pencil trick! I did this with over 400 students in one week….and every single student enjoyed making predictions and participating in this experiment. It is fun for all ages!
You will need:
- Several very sharp pencils~they do need to be sharp to separate the polymers in the bag. This is essential to the success of the pencil trick. I try to have at least 5-10 pencils ready.
- 1 plastic bag of any size. Quart size to gallon size work the best.
- Water
- An assistant to hold the bag. It has to be someone who will hold on to the bag and not drop it when you quickly force the pencils through the bag!
How can you make this experiment work?
Fill the plastic bag half full or no more than three quarters full. This is very important. The water holds the sides of the bag out and allows the pencil to push through the polymers that make up the bag.
This is a fun time to build anticipation with your audience as you get ready to puncture the plastic bag.
Get your assistant to hold the bag. I suggest a two-handed pinch at the top of the bag. For the first round you are the pencil pusher. Simply push the pencil through one side of the bag through the water and then through the other side of the bag. Push the pencil quickly with force! If you push the pencil slowly there is a chance the experiment will not work. Don’t be afraid just push the pencil through the plastic bag. Leave the pencil in place.
If you don’t leave the pencil in place you will have a water spout….and no one will be impressed… and you will also have a mess to clean up! Anyway you get the picture.
You can continue to push pencils through the bag. I have put a few in a quart size plastic bag. By that I mean 12! You can put pencils through both sides of the bag. If you have the students put pencils through the bag make sure they push the pencil through both sides of the bag. The pencil should be sticking out both sides of the plastic bag.
How it works:
The plastic baggie is made of polymers that stretch and separate just enough to allow the pencils to pass through. It reminds me of putting a pencil through a sweater. The strands of yarn are pushed aside but the weave of the sweater hugs the pencil. You can also think of the polymers as cooked spaghetti. If you put a pencil in a bowl of cooked spaghetti the spaghetti noodles would slide to the side. These polymers behave in the same way.
The polymers are permanently separated and leave a hole in the plastic baggie. That is why the water will pour out if the pencils are pushed completely through either side. If you want to see what happens please stand over a sink when you remove the pencils!
I like to walk around the classroom or conference presentations with the plastic baggie full of pencils…it is fun to demonstrate a science experiment. It always encourages questions about science. This trick will also make you very cool at picnics and Bar-B-Ques etc.
If you would like to read about more fun activities please check out these posts:
Paper Shape Builders Cut, Paste and Build STEM Activity
Who Invented the Super Soaker?
Thanks for reading. I’ll be back to share more ideas with you!
Sarah Winchell
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