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.