What is the viscosity of golden syrup?

30th January 2003

Viscosity is the speed of the flow of a liquid of gas. Viscosity is a factor which controls the liquid/gas’s resistance to flow. The lower the viscosity of a fluid, the runnier it is.

An Irish physicist George Gabriel Stokes (1819-1903) invented a method of measuring viscosity by timing a ball falling at a constant speed through a liquid. Stokes studied the forces exerted on a spherical object, namely a ball bearing as it moved through a fluid, or when a fluid moved past it. Stoke then came up with a relationship called Stoke’s law to describe the viscous drag:

=Radius of the sphere

=Velocity of the fluid

=Coefficient of the fluid (viscosity)

To obtain the viscosity the following equation can be used:

When a body moves with constant velocity through a fluid, it experiences a frictional drag force which opposes its motion. For a sphere of radius r when moving with velocity v in a fluid of viscosity h, this frictional force is equal to 6p hrv.

Diagram of forces on the Ball Bearing Upthrust Viscous drag

Weight

The SI units of viscosity are Nsm-2.

AIM- To investigate the viscosity of golden syrup, and how factors such as temperature of the golden syrup affect the viscosity.

Before I carry out the experiment I will need to know the following:

Temperature of the syrup- I will find this by using a thermometer and heating the syrup in a water bath until the desired temperature is reached.
Density of steel- I will find this out by using the formula Density=mass/volume.
Size and mass of ball bearing-I will find the size of the ball bearing by using a micrometer screw gauge. To find the diameter. I will find the mass of the BB by using scales.

I will use the same densities for BB and the syrup, as it will not vary a great deal.

APARATUS-

Two ball bearings of different sizes and masses.
Three water baths
0.2M cubed of golden syrup
Large test tube
Clamp and retort stand
Thermometer
Stop clock
Ruler
Magnets

The ball bearing size and mass, and the temperature will be my independent variables. The viscosity and velocity of the ball bearing will be the dependent variables.

I will be using 2 ball bearings with different sizes and masses. This was I will be able to rule out anomalous results, for example is the ball bearing is too light it may just sit on top of the syrup. If it is heavy, the terminal velocity may be so high it may travel through the syrup so fast I would not accurately be able to measure the time taken. I am using golden syrup as from my background knowledge I know it is very viscous at room temperature, and its viscosity will change dramatically with any temp change. I will be using water baths to heat up my syrup as their temperature will remain constant, and I will be able to choose the desired temperature. If I was too use a Bunsen burner the water would not remain at a constant temperature, which would make my results inaccurate, as all the tests would be done at different temperatures. I will be using a large test tube to hold my syrup as I will easily be able to measure how much syrup I put in there. I will use magnets to get the ball bearing out of the syrup, as this will involve minimal loss of syrup and mean I can use the same ball bearing for each experiment, this will help rule out anomalous results caused by using different balls.

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I will mark a line on the test tube 0.1M from the top. The second line will then be 0.05M under the first line. I will mark it 0.1M down as I want to give time to allow the BB to reach it’s terminal velocity. I want the BB to be travelling at its terminal velocity rather than accelerating, as it will be fairer. If all the velocities were different I would not be able to use Stoke’s formula correctly. If the terminal velocity is too high I will not be able to accurately measure the time, as the BB will travel so fast through the 0.05M distance I will not have enough time to accurately start the clock from when the BB moves past the 1st line to when it moves past the 2nd line. I will try to use relatively light balls, as their terminal velocity should be slower. I am not going to heat the golden syrup past 60oC as I predict the golden syrup will become so viscous I will not truthfully be able to measure the time taken to travel from the 1st line to the 2nd as it will be too fast.

I will use the same apparatus for each experiment as this will rule out inconsistent results due to variations in the equipment.

I will repeat all tests 3 times. This way I can rule out any anomalous results, which may occur. I will then find an average viscosity by calculating the mean. This will make any patterns clearer to see on a graph. I will still construct graphs to show all the results, as I will be able to easily pick out anomalous results.

Once my results are recorded in a table I will round them to 4decimal places. I think this is accurate enough. If I was any less accurate some of my results would end up as 0. However anymore accurate and I may be lying as I cannot possibly have recorded everything that accurate. I will only be able to calculate the time taken to travel a distance of 0.05M to 2 decimal places, as this is as accurate as my equipment will allow. I will have to assume each ball bearing travels a distance of 0.05M, but realistically it is likely this number will vary by a couple of mm, as measuring by eye is not that accurate.

SAFETY:

Exercise caution when working with hot liquids. Wear protective gloves when handling anything hot.
Do not walk around the laboratory with hot liquids
Wear goggles when needed in case the liquids spit when hot.
Make sure all equipment is stable and secure before carrying out the experiment.

I have worked out the information I will need to be able to calculate viscosity:

The temperatures of all the syrups. I worked these out by using a thermometer and then recorded them in a table.
I worked out the diameters of the ball bearings using a micrometer screw gauge. They were 0.010M and 0.0060m. Their masses where 0.0030kg and 0.0011kg respectively.
Density of steel-I worked this out by using the formula density=mass/volume. For the ball bearing with a diameter of 0.010M the mass was 0.0030kg .The volume of the ball bearing was 5.23667x10-07 M cubed. This means the density is 5671.5468 kg/m3. For the ball bearing with a diameter of 0.006M the mass was 0.0011Kg.The volume was 1.13112x10-07 M cubed. This means the density was 9282.8347 kg/m3.

I will be calculating the viscosity using the non-graphical method as in my opinion it is more accurate than the graphical method. The graphical method will not be as accurate as it will rely on my eye reading from the graph, so I may read it imprecisely.

METHOD-

Fig 1

Set up apparatus (see fig 1)
Using golden syrup at room temperature pour in 0.2m of golden syrup
Drop the chosen sized ball bearing in to the syrup.
Start the stop watch when the ball bearing reaches the first line
Stop the clock when the BB reaches the second line (0.05m below the first line)
Record the time in a table
By using magnets drag the ball bearing up to the top of the test tube. Take it out and wipe clean, rinsing it under a little water if needed.
Repeat the experiment 3 times, recording the results each time.
Repeat from step 3 but using a different temperature of syrup. Use 4 different temperatures.
Repeat from step 3 using a different sized ball bearing.
Once all results are recorded work the viscosity using the formula

RESULTS:

TABLE TO SHOW RESULTS USING A BALL BEARING WITH DIAMETER 0.0100M

TABLE TO SHOW RESULTS USING A BALL BEARING WITH DIAMETER 0.0060M

Graph 1- Graph to show all results for viscosity VS temperature for a ball bearing with diameter 0.0060M

Graph 2- Graph to show all results for viscosity VS temperature for a ball bearing with diameter 0.0100M

Graph 3- Graph to show mean average of viscosity against time for a ball bearing with diameter 0.0060M

Graph 4- Graph to show mean average of viscosity against time for a ball bearing with diameter 0.010M

Conclusion-

Graph 1- From this graph I can see viscosity decreases as the temperature. From my graph I can clearly see a negative correlation. There are no anomalous results to be noted. I can see the test using room temperature syrup was a lot more viscous, around 90 NSM-2 more when the temperature was 47oC higher.

Graph 2- From this graph I can see I clearly I have an anomalous result (circled). It does not fit my line of best fit, as it is over 100 NSM-2 less viscous than my other 2 results. However with my line of best fit in place I can see this produces a negative correlation. The syrup gets less viscous the warmer it gets.

Graph 3- This graph shows my mean averages using a ball bearing with diameter 0.006M. It shows a negative curve. I can see the viscosity decreases severely from 94NSM-2 to 6NSM-2.

Graph 4-This graph shows a negative curve. It shows my mean average for a ball bearing with size 0.01M). The viscosity drops from 203 NSM-2 to 9 NSM-2.

From my results I can see that the smaller BB (diameter 0.006M ) traveled faster than the larger BB (diameter 0.01M). For example at room temperature (20oC) the average speed of the larger ball to travel 0.005m was 33.98s. The average speed for the smaller BB was 26.00s. I think the smaller BB traveled faster as it has less syrup to displace. It could also travel through smaller spaces between particles. Both my ball bearings showed the same pattern though, that they could travel faster through syrup, the lower its viscosity.

I had several problems with my apparatus; I had to modify the set up. For example after I carried out the 1st experiment, the syrup had cooled by a degree at least. To counteract this I placed the test tube back in the water bath after each experiment and allowed it to return to the desired temperature. I did this as it would not have been a fair experiment if all the experiments were at different temperatures but I grouped them all under the same temperature heading. Another problem was every time I took the ball bearing out of the syrup; it was still coated in syrup, which I then rubbed off. This meant by the last experiment I would have lost a considerable amount of syrup. Every time I changed the temperature I measured the amount of syrup, and added more if I needed to. I then heated it to the correct temperature, as the added syrup would have been colder. If I had not added the extra syrup the tests would have been unfair because if too much was lost the BB may have not reached its terminal velocity. I heated the original syrup and the new because no only would the temperature of the original syrup have cooled while I was adding more, the new syrup would be of a different temperature. This means the BB would be traveling through to different viscosities, and the velocity would change, so it may not reach its terminal velocity.

I have one anomalous result. It can clearly be seen on Graph 2. The viscosity is a lot lower. There are several reasons for this. I think when I took the ball bearing out of the syrup after an experiment and rubbed it. This rubbing will have created friction, which will have heated the ball bearing. The hotter the ball bearing the faster it will travel through the syrup, like a hot knife travels faster through butter than a cold one. If I were to repeat the experiment I would place the ball bearing in a beaker of room temperature water after each experiment, for one minute. This would allow it to change to a known temperature and make the experiment fairer as I would be getting rid of another unnecessary variable. When I dropped the ball bearing in the test tube the ball bearing sometimes fell to one side and traveled down the side of the tube, rather than down the center of the tube. As it was rubbing against the side it would have created friction, which would have slowed it down. This would have made the velocities different due to the differences in friction rather than just the viscosity of the syrup. This would have been unfair. In a future experiment I would use a straw and hold it over the center of the tube. I would then put the ball bearing down the straw. The only drawback with this would be it had a velocity already. If I knew this velocity however and it remained constant for each experiment I would be able to use this. Another draw back of my method was the syrup might have been heater unevenly. This would mean the ball bearing would be traveling through areas of high viscosity to low viscosity and the velocity would have varied depending on where I measured it along the tube. I tried to stir the syrup in the test tube to disperse the heat evenly, but I cannot be sure how well I did this, and I may have introduced air bubbles, which is a ball bearing fell through would speed it up.

From my graphs I can see that viscosity decreases when the temperature of the golden syrup increases. This is because the syrup becomes less dense. As the liquid heats up the particles gain more energy so can move further apart. This allows a ball bearing to move more easily through it, as the particles are not so tightly packed. The viscosity of a fluid is caused by electrical attraction among molecules. This makes it harder for the molecules to move apart. When the temperature increases, molecules vibrate and move about more vigorously, which tends to break the temporary bonds that form among molecules. My graphs give me evidence for this, as I can clearly see on all my graphs the viscosity decreases as the temperature increases. For example my ball bearing (diameter 0.01M) took 39.65s to travel through syrup at room temperature and just 0.5s when the temperature was 57oC. It could travel faster as the bonds between the golden syrup particles are weaker so the particles are further apart, allowing space for the BB to travel through.

I would like to have measured both ball bearings at the same temperature, and in clear denominations e.g. every 10 degrees. However the apparatus limited me. The water baths were found to be inaccurate, usually 3 or 4 degrees out from the desired temperature. Also I had to use different water baths as I did my experiment in 2 phases. This meant I could not measure the same temperatures for both sized ball bearings, so I could not compare them accurately. By using a clock that only went up to 2 decimal places I limited the accuracy of my results. Also I was only reading the results by eye, so the results are likely inaccurate. If I were to repeat the experiment I would use a data logger to measure the time taken for the ball bearing to travel the 0.005M distance, as this would be more accurate and reliable. I would also like to have used a longer test tube, so the ball bearing could have traveled further before I timed it. This would have me be sure it had reached its terminal velocity.

I think I carried out this experiment well, but was limited by my apparatus. I think if I were to repeat the whole experiment it would be more accurate. However my results are similar to those obtained by my classmates so I am fairly confident my results show the correct trend.

An alternative to this experiment would be to use a bowl rather than a narrow test tube. As the ball bearing travels through the syrup it must displace the syrup in its path. This requires force. I think if I used a bowl there would be more space for the syrup to be displaced to the ball bearing may travel faster. I would like to investigate this theory and see if it is correct.

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