What makes an oil runny?

I am going to investigate what properties make oil runny and also the viscosity of oils.

There are a number of variables that could influence my test some of which include,

* The temperature

* Length of slope

* Gradient of slope

* Amount of hydrocarbons present

* Amount of oil on the slide

I am going to test the amount of hydrocarbons in the oil. I am testing this because the other four variables would be to hard to control, such as the temperature and if I were to test the gradient I would have to measure the exact degree and have a reliable stand or propping device to hold it. Therefore the amount of hydrocarbons is the simplest because I just use a different oil each time.

I predict that the lower number of hydrocarbons present, the faster the oil will reach the bottom of the slide. I think this because if you think of a tray at an angle, and then it had a layer of sand over the whole of the tray (but the sand doesn’t move) then a bag of single marbles were tipped onto the top of the tray and let to roll down. Some would get stuck in the sand but most

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would just roll freely to the bottom. Then picture another bag of marbles the same size but this time each marble was super glued to another marble so that they were in pairs. Then this bag was tipped at the top of the tray, (with fresh sand and free of single marbles) the marbles wouldn’t roll as freely as they have a double bond and there is more friction present on the two marbles. This time, more would get stuck but most would still reach the bottom. Then if I carried on doing this for a lot more of the marbles up to about ten then in the end no marbles would roll and they would all get stuck due to the amount of friction.

To make my test a fair one I will keep all the variables that are above the same such as keeping the slide at a constant height and doing the test in the same part of the room to keep the temperature the same. Also I will use the same dropper, keeping the same aperture and therefore having the same size drop each time.

For my apparatus I will need:

* Several slides

* A time keeping device

* Different types of hydrocarbon oils

* A dropper/pipette

* Something to hold the slide secure

* Paper towels (for mopping up)

For the measurements I will use seconds and milliseconds and minutes if necessary. All answers will be to 2d.p and I will do each run three times.

The method is a straight forward one. I will find a solid structure that is of satisfactory height and then carefully position my slide against it making sure not to break the slide:(. Then I will drop an amount of oil onto the slide and when it reaches the start line I will begin to time. Then when it reaches the bottom I will stop timing and proceed to record the results in a table. Then I will repeat this test two more times and after that move onto another of the oils.

I have performed a pre-test with only one oil to get a wide range of results and they are as follows: On paper

I have performed the pre-test so that I can get all the necessities for the experiment such as what sort of an angle to place the slide at, how many drops of oil and other things that relate to the experiment.

To keep my test a safe one I will firstly be sure to handle the slides carefully as they are fragile and could snap but other than that the experiment is relatively safe.

Obtaining Evidence

Time in seconds from start to finish. cm/s

Oil Name

Test 1



Avg. Time

Avg. Speed































All the results are close enough to take a good average and none need to be repeated.

If I obtained a separate set of results I could plot them against each other and get a contrast of the two sets.

Analysing Results

Graph on separate sheet

My graph shows that as the time of the oil is slower then the average speed decreases so it is slower. My graph slows a negative correlation when the speed is on the vertical axis and the time is on the horizontal axis.

My results support my prediction as I predicted that the longer the chain of hydro carbons was then the longer time it would take to reach the bottom of the slope.

Evaluating Results

I think that my results are quite accurate as we have compared with other groups and our results are similar.

There are no anomalous results on the graph.

My results are reliable because if another word for reliability is repeatability and we repeated them three times and they were always about the same value.

The procedure was simple but effective, the slide was a good length and we found our own angle at which to set it.

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