Physics Coursework: Investigating the effect of Temperature on the Viscosity of Syrup Preliminary experiments: The first thing I thought about when beginning the investigation was how I could measure viscosity accurately using the equipment that was available to me. I decided on timing a cylindrical jar rolling down a one-meter slope. I started by adjusting the slope until I was happy that the gradient was not to steep and not to shallow so I could obtain accurate timings without waiting too long for the syrup to roll down the slope.
I eventually settled on a height change of 6. 4cm, which meant a gradient of 0. 064(6. 4/100). I also investigated the effect of the amount of syrup in the cylinder. First of all I used an empty jar, which rolled down the hill at a constant speed no matter what the temperature. I started by using very little syrup, but found that the jar rolled down the slope too quickly. I then tried the jar half full, where the jar rolled down the slope, accelerating and decelerating at different stages down the slope, and even stopping completely in a few places.
I then decided to use a full jar of syrup. This jar rolled down the hill at a constant speed. So that I could start to make some predictions about what was happening in the jar I cooled the syrup down and repeated the experiment. When the jar was almost empty and half full the jar did roll slower than at room temperature. However when the jar was full it rolled at the same speed. I then heated the jar up and repeated the experiment. When the jar was nearly empty and half full it rolled quicker than at room temperature.
Again when the jar was full it rolled at the same speed. I therefore decided to use a jar half full of syrup. I decided to investigate why the temperature did not affect the syrup when the jar was full but did when it was empty. I discovered that when the jar was full the centre of gravity in the jar was constant, creating a constant turning force. However when the jar was half empty the syrup had room to flow, therefore changing the turning force on the jar throughout the experiment. The diagram below shows the effect of the centre of gravity on the turning force.
Now that I was satisfied with my preliminary results I decide to start taking some more accurate measurements using the results from my preliminary experiment. The apparatus is drawn below. When heating the experiment I discovered my next problem. Whilst heating the experiment in a water bath, the Pyrex beaker cracked at 74i?? C. As Pyrex beakers are made to withstand high temperatures I decided that the crack must have been due to (mechanical). I then discovered that as the experiment was being heated there was a bubble of energy forming under the dome shaped bottom of the jar.
When the bubble became big enough it lifted the jar in the water bath and dropped it in the bath, causing the crack. I therefore decided to heat the water bath to boiling first, turn of the flame, then slowly hold the jar in the bath until it was warmed, and then slowly lowered the jar into the bath. I left the jar until the temperature of the syrup was about the same as the temperature of the water, which took around 5-10 minutes. I repeated this until the syrup was 75i?? C. I then rolled the jar down the slope and recorded the times taken at 2i??