What Makes An Oil Runny

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We set up the apparatus as above. We then filled the capillary tube with oil. We then put a small ball bearing in to the tube and used a magnet to pull the ball bearing to the 22cm mark and checked the room temperature. We allowed the ball bearing to fall through the oil by removing the magnet. The person removing the magnet would count down in order for the person timing to be able to tine the experiment more accurately. We decided to take 7 readings and use only the five readings closest to each other and that were anomalies we repeated, so that on the whole we had a more accurate set of results. To make the experiment safe we all wore safety goggles and were careful not to expose the oil to a naked flame. We also ensured that we didn’t get


My hypothesis is that a body passes through a thick oil more slowly than a thin oil. Therefore the larger molecules are the less runny or more viscous. To support this theory I give the following examples C8H18 is a liquid and C32H68 is a solid. This helps to support my theory because the structure of the C32H68 is the same, just longer than C8H18 so the longer molecule of C32H68 is tangled like a piece of spaghetti and it is so tangled that it can’t move and this makes it a solid the same idea works for the viscosity of the alkane liquids we tested in our experiment (they are more viscous because the longer molecules are more tangled). Also inter molecular forces are attracting other polymers more than smaller polymers of even monomers would so this causes more energy to be required to push the oil out of the way of the ball bearing moves more slowly in C16H34 than it would inC6H14.


I found that the larger the molecule the longer it takes to roll down the capillary tube. This shows that the intermolecular forces are stronger in a long polymer than a shorter one. The graph I have drawn from my results has a curve to start with and then becomes a strait line. The graph shows that the larger molecules create more resistance towards the ball bearing and this shows that larger molecules are less runny therefore it is molecule size that dictates runniness.


The oils that are thin have smaller molecules than the thick molecules. This is about surface area and that molecules with a larger surface area can’t move amongst each other as molecules with a smaller surface area therefore molecules with a large surface area need to be given more energy to be moved aside by a ball bearing or any thing else passing through the oil this at affects runniness. Also polymers such as C120H242 are viscous because they are so long that they get so tangled up that it is difficult for a body to pass through it in fact C120H242 is so tangled up that it is a solid.


My results showed me that my method was good because my results were closely grouped and consistent with my hypothesis.

The anomalous data was caused by either operator error in recording the timings or the friction of the ball bearing travelling down the tube which cold have caused the oil to warm up and change its viscosity.

The method used isolated one variable, time, and so demonstrated a good scientific method in this experiment.

Suggested changes to improve the reliability of the evidence are:

1. To put the tube in a water bath to ensure that the temperature remains constant.

2. To design an automatic release mechanism using an electromagnetic release with an induction sensor at or near the base of the tube coupled to a timing device.

3. The viscosity of the oil could change as the experiment progresses because the ball bearing may case some of the molecules to break down into smaller molecules. This process is known as cracking and normally requires high temperature and a catalyst but could occur on a limited scale under the conditions of this experiment. This could be further investigated by repeating the experiment with a wider tube and a lighter ball bearing to reduce the effect of friction.

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