THE experiment!

Zip lock bag A filled with 1l of water










Skewer pierced through spot A1.










Side view of skewer pierced through spot A1.










2nd skewer pierced through spot A2.














3rd skewer pierced through spot A3.












All 3 skewers in zip lock bag A.













Skewer in spot C1












2nd skewer in spot C2.












3rd skewer in spot C3












All 3 skewers in zip lock bag C.











Skewer in spot D1











2nd skewer in spot D2.










All 3 skewers in zip lock bag D

Designing for the final experiment

I did a template for the type of zip lock bag I am using as it saves more time and is also more accurate.






Close up shot of the quarter section of the zip lock bag which I am working on.










Zip lock bag A















Zip lock bag B














Zip lock bag C















Zip lock bag D

Approaching from a different angle

If I am testing on the durability of the bag, then I should test on how many skewers can be poked through it and the amount of water that spills out.



What I did was that I drew squares measuring 2cm by 2cm on the zip lock bag.










I pierced the first skewer in at the bottom row left most square.













The second skewer went in through the next alternate square













And the 3rd one the next alternate square.







In the end it turned out to be this messy and undesirable zip lock bag.














However, poking at spots gave me another idea. Does the distance between the spot where the skewer is poked and the center of the zip lock bag affect the amount of water that spills out?

Consultation with Ms Tan

Getting nowhere with my experiment. So I booked a session with Ms Tan and together we discussed my experiment. A few of the more important things Ms Tan pointed out:

1. I said 'normal plastic bag' when actually referring to the sandwich plastic bag. Ms Tan corrected me as normal to her was the NTUC shopping bag. Everyone has different interpretation of things, so terms used have to be very specific.

2. There are different plastic grades. Maybe I can expand on this.

3. What am I testing for by poking a pencil through a bag? Is it the durability of the bag?

4. I need to set constant variables for my experiment. E.g., size of plastic bag, amount of water initially, amount of time the pencil is poked into the bag

5. May want to consider using skewers instead of pencils because they are smaller in size

Elevator pitch

We have to make a speech in front of the the whole class to try to sell our experiments to our classmates. So I wrote out a speech that is under the time limit which is 3 minutes.




My project is studying materials/ properties that are present inside different types of bags. Bags, as in grocery bags, not handbags. Ziploc bag, sandwich bag, coffee bag, ntuc bag.

My inspiration came from a Steve Spanglers’ experiment, where he held a ziploc bag filled with water over a volunteer’s head, and poked a pencil straight through the bag. No water spilled out.

I have confirmed that this experiment truly works, but what I did was just sticking a pencil through a bag filled with water, with not quantifiable results. This was just a preliminary experiment. I will need to do it again, this time taking note of the independent variables and such. They include, size of bag, amount of water in bag, and having a way to measure the amount of water that spills out. Also, I need to know the materials of the bags, in order to compare them with their properties, because different brands have different compositions of materials.

Thus, right now I don’t have a new hypothesis since my project has taken on a different angle.

Further research on the material of Ziploc bags show that it is mostly made of a material called polymer. To make complicated things simple, polymer has a continuously-linked backbone that allows the pencil to slip in between the molecules strands without tearing the other parts of the bag.
Furthermore, the long chains of molecules even seal back around the pencil to prevent the water from leaking out. This was evident as when I poked a pencil though a dry piece of plastic bag, the edges of the hole created could be seen following the pencil through, leaving the hole snug and fitted.

Plastic bags are often made from polyethylene, which consists of long chains of ethylene monomers. Ethylene is derived from natural gas and petroleum.

I did the same experiment with a paper bag. Water had started dripping out even before the pencil was poked in. When the pencil was poked in, water just started spilling out. This was because the hole created by the pencil just tore and the hole was bigger than the diameter of the pencil.

Paper is mainly made up of cellulose which has weak hydrogen bonds. This may causes a whole paper bag to tear when a sharp pencil is poked through it. Also, wet paper has weak fibres that will cause it to be torn more easily than dry paper.