The effect of the temperature on the viscosity of the syrup
Aim: In this investigation I will be investigating the effect of temperature on the viscosity of golden syrup by measuring the rate of descent of a sphere through the syrup at different temperatures.
Viscosity is an internal property of a fluid that offers it resistance to flow. The flow of fluid involves different components of the fluid sliding against each other, as if they were in layers at different velocities. The ease at which the fluid flows is dependant on how easily the layers slide against each other. The lower the viscosity is the less the occurrence of friction between the layers as they slide against each other. Hence the easier the fluid flow. In contrast when there is a greater occurrence of friction between the layers, the flow of the fluid becomes more difficult to maintain and as a result they slide each other with less velocity, which gives it a higher viscosity.
Flow is harder to control in syrup whereas in water the flow is much simpler. Hence the syrup is more viscous than water.
In fluid the molecules move randomly. This includes the molecules which are at rest as well as those which are moving with a velocity. In addition to the random motion of the molecules a drift motion also occurs and it carries the molecules along with the flow. During the drift motion, molecules tend to move from layer to layer due to their random movement. Consequently for each molecule that shifts into another layer in one direction, another molecule will shift layer in the opposite direction. For instance, a molecule which is moving at high velocity layer shifts to an adjacent layer which flows with a lower velocity. In turn, a molecule that moves in a low velocity layer will shift to the adjacent layer which is at high velocity.
The variation in temperature affects the viscosity of a fluid. Increasing the temperature lowers the viscosity of the fluid. The fluid becomes thinner, less viscous and flows more freely. This is because molecules gain energy when the temperature is increased, so that they are moving at a high velocity and collide more successfully. However, when the fluid becomes cooler the viscosity increases and as the fluid becomes thicker, the rate of velocity becomes lower and doesn’t flow as easily. This is due to the reduction in energy from the molecules, which in turn reduces the movement of molecules. Less collisions occur, so that the molecules are more closely packed together.
Stoke’s law can be used in situations of steady motion. Therefore it relates to the motion of sphere through viscous liquid. It can be used to find the viscosity of the same liquid at different temperature.
delta p = difference in density between the sphere and the liquid
g = acceleration of gravity
r2 = radius of sphere
v = velocity = (distance sphere falls) / (time taken for it to be fall)
When a sphere falling vertically under gravity in a viscous fluid, there are three forces act on it known as:
- it’s weight W, acting downwards
- the upthrust U due to the weight of fluid displaced, acting upwards
- the viscous drag F, acting upwards
The resultant downward force is (W – U – F) and causes the sphere to accelerate until its velocity is zero, and so the viscous drag reaches a value of, W – U – F = 0. at this point the sphere reaches it’s terminal velocity and so it continues to move with a constant velocity.
Mass of the sphere – Changing the mass of the sphere will change the weight of the sphere. An inconstant weight will have an impact on the velocity at which the sphere travels since the sphere travel with a different force each time.
Size / surface area of object – Varying the surface area of the sphere will affect the velocity at which the sphere travels. This is because when the surface area is increased it means the friction force opposing the motion of the sphere will be increased too. In effect, the time it takes for the terminal velocity to be reached alters.
The volume of Syrup – Volume should be kept the same, because changing the volume will change the density of the syrup, which is involved in Stoke’s law equation.
Position of descend – According to the ‘laminar flow’ theory, which I have stated previously, the position of descent should also be the same in each case. Since the layers travel in different velocities, from zero at the wall to maximum at the centre, positioning the descent of the sphere in different places each time will affect the rate of increase in velocity due to the increase in temperature.
Initial speed at which the sphere descends – Releasing the sphere at same velocity every time is important. Otherwise the increase in rate of velocity will vary since the temperature will also vary. This is because the time taken for terminal velocity to reach varies. Hence it will also affect the viscosity of the syrup.
Temperature of the syrup – When the temperature is altered, the speed at which the molecule travels also changes. In effect the viscosity of the syrup also changes.
To have an idea of the effect of different temperatures on syrup I will carry out preliminary work. This would enable me to determine appropriate ranges such as choosing suitable sized equipment and correct volume of syrup for the final experiment. It would also enable me to make my experiment as efficient as possible in order to obtain the best possible results.
This is a preview of the whole essay
- 1 liter Beaker
- Electric heater
- Weighing machine
- Vernier calliper
- Measure the mass of the beaker without syrup
- 5 cm above from the surface of the beaker mark a line
- Measure the mass of the beaker with syrup
- Measure the mass of the sphere
- Place the thermometer inside the beaker containing syrup
- Turn the electric heater on and place the beaker on top of the electric heater.
- Stir the syrup and heat it until it reaches to a temperature of 800
- Remove the beaker from the electric heater and place it on top of the stand
- Measure the vertical part (length) of the beaker that is only filled with the syrup
- Drop the sphere inside the syrup as well as starting the stop watch
- Stop the stop watch as soon as the sphere crosses the line that is marked on the beaker
- Record the time
- Wait until the temperature falls down to 700
- Repeat the same procedure as for the 800
- Now repeat the whole procedure for each temperature as follows, 800, 700, 600, 500, 400, 300 and 200
Use thick cloth when removing the beaker from the heater to prevent getting burnt. Situate the beaker and stand it carefully at the centre of the stand, so that it does not slip away. Extra care should be taken when dealing with the beaker such preventing it from breaking.
Table of results for Preliminary work
Conclusion from the preliminary work and improvements suggested for the final experiment
During my preliminary work I have found out that there are certain aspects of my work which need to be improved for the final experiment, so that I can produce the best possible results. It was inappropriate for me to use 1 litre beaker since it only allowed the sphere to travel for 10cm. The syrup was very lowly viscous at temperatures of 600, 700 and 800 and so the sphere traveled with a very high velocity. As a result the time taken for the sphere to travel was less than a second for 600, 700 and 800. The viscosities at temperatures 600 and 700 had the same value of 2.82 Nsm-2. Even the difference between viscosity at 700 and 800 was only 0.44. This doesn’t provide sufficient results because the change in viscosity between each temperature is small. In order to improve this in the final experiment I will use a 30 cm measuring cylinder. This would enable the sphere to travel further, so that the viscosity for different temperature will vary enabling me to see a trend between them.
To improve my final experiment so that a sufficient set of results can be achieved, I will change the range of the temperatures that I am going to investigate. Whilst 30cm measuring cylinder will provide a longer distance, it only takes a short time for the sphere to decent through the syrup. Therefore in the final experiment I will investigate the temperature from 500 to 50, since at 500 the viscosity will be higher than at 800 and hence the sphere will move more slowly. This would allow me to record the time taken for the sphere to descent more accurately. The temperature interval will be 5 every time, so 500, 450, 400, 350… to 50.
It was noticed that when the sphere was removed by descending the magnet (attached to a string) into the syrup, an amount of syrup was also removed. Although it was only a small amount of syrup, the density will be reduced and changes the viscosity of the syrup. In particular this would affect the viscosity of the syrup dramatically at 200. As the sphere is removed from 800 to 300 the amount of syrup removed accumulates consecutively. In order to eliminate this error in the final experiment, I will use a magnet so that the sphere will remain attracted to the it throughout the process of removing it. In order to do this I will be holding the magnet on the outside of the measuring cylinder. Although this prevents the loss of syrup from the measuring cylinder, a small amount of syrup is still lost as the syrup becomes attached to the sphere whilst being removed. To improve this experiment further, the scale should be constantly monitored and further syrup should be added to maintain a constant level of syrup.
Different parts of the syrup travels at different speeds. So it was important to consider the position which the sphere had been dropped at. Varying the position of the descent of sphere altered the increase in rate of velocity due to an increase in temperature. Dropping the sphere by the edge of the beaker took even longer. This was due to the extreme build up of friction between the side of the beaker and the syrup. To alter this error in the final experiment the sphere should be dropped at the centre for each experiment. This would ensure that there will be no effect in the increasing rate of velocity at which the sphere travels at.
I have tried three different spheres with different masses 4.08g (sphere 1), 8.9g (sphere 2) and 16.7g (sphere 3) at 500. From the results I chose to use the sphere of 4.08g for the final experiment. Since 4.08g sphere traveled at a very slow motion to be timed accurately. Whereas the other masses of sphere traveled at a higher speed.
The measuring cylinder will be filled with syrup up to 5cm beneath the top of the tube. This will ensure that no syrup will be spilled from the top and the surface of the syrup is high enough to allow the sphere to be released from rest.
I have also tried to find out whether the sphere accelerates whilst traveling through the syrup. In order to do this I have videoed the sphere was traveling through the syrup at 150, and then I have investigated how long it will take for the sphere to travel every ten centimeters. By doing this I was able to produce the following table:
At high temperature the viscosity of the syrup will be low. This is because the molecules gain energy at high temperature, which reduces the syrup’s resistance to flow, since the friction between the layers is also reduced. This is due to a gain in energy. As a result the molecules move at a higher velocity and drift motion occurs highly. This change increases the rate of flow, decreasing the viscosity of the syrup.
Lowering the temperature of the fluid increases the viscosity of the syrup. The molecules lose energy at lower temperature which in effect increases the syrup’s resistance to flow. This is due to the increased friction between the layers caused by the gain in energy. Consequently the molecules move with a low velocity, as the chances of a drift motion occurring also decreases. This change lowers the rate of flow of the syrup.
The preliminary work that I undertook and my understanding of the viscosity of fluid has enabled me to predict that as the temperature decreases the viscosity of the syrup will increase. So the value of viscosity be smallest at 500 and highest at 100, since the temperature I choose to investigate for this investigation lies between the ranges of 500 and 100.
- Measuring cylinder
- Weighing machine
- Graduated thermometer
- Micro meter
- Vernier calliper
- Stop watch
Improved method using for Final experiment
- Measure the mass of the measuring cylinder using a weighing machine
- 5 cm above from the surface of the measuring cylinder mark a line using a marker. Also, mark a line 5cm below from the top of measuring cylinder. Fill the syrup into the measuring cylinder until it reaches the marked line on the top
- Measure the mass of the measuring cylinder containing the syrup using a weighing machine
- Place the thermometer inside the measuring cylinder containing syrup
- Fill up the kettle with water and heat it
- Transfer the water from the kettle into the jug
- Place the measuring cylinder inside the jug
- Stir the syrup and heat it until it reaches a temperature of 500
- Remove the measuring cylinder carefully from the hot water and place it on top of the stand so that the lined marked on bottom of the measuring cylinder is at eye level.
- Measure the length of the syrup when it touches the bottom of the cylinder and also at the top of the measuring cylinder, using a ruler.
- Release the sphere inside the syrup as well as starting the stop watch
- Stop the stop watch as soon as the sphere crosses the line that is marked at the bottom of the measuring cylinder and record the time
- Once the sphere has reached the end, separate it from the syrup. To do this, hold the magnet by the side of the measuring cylinder so that the sphere becomes attracted to it. Once it becomes attracted, drag the magnet upwards so that the sphere will come up with it as well. When the sphere reaches the top of the measuring cylinder, remove it using tweezers.
- Measure the length of the syrup and add if necessary more syrup to maintain the original density of the syrup. Stir the syrup with a thermometer to maintain an equal temperature throughout the syrup mixture.
- Wait until the temperature falls down to 450 and repeat the procedure as for the 500
- Repeat the whole procedure for the following temperatures three times: 500, 450, 400, 350 , 300, 250 and 200
- Now place the measuring cylinder into the freezer and remove it when the temperature reaches 50. Then repeat the same procedure as for 500 for 150, 100and 50.
- Repeat the whole procedure for the following temperatures three times: 500, 450, 400, 350 , 300, 250, 200, 150, 100and 50
The independent variable in this investigation will be the temperature of the syrup. The dependant variables that I will be controlling throughout the experiment will be the mass of sphere, surface area of the sphere, the volume of the syrup, position of descend and the initial velocity at which the sphere descends. Controlling the dependant variables enable me to carry a fair test, so that only the change in temperature of the syrup will contribute to the viscous effect on the syrup.
Repeating the experiment for each temperature three times will allow me to form an average, with a set of reliable and accurate results.
- Care should be taken when pouring hot water from the kettle. To avoid burning yourself wear gloves.
- Be careful when using the thermometer, as it is loosely situated inside the measuring cylinder and could tip over the whole content inside, including the hot syrup.
- When removing the sphere with the magnet, extra care should be taken as it could also lead to the tip over of measuring cylinder.
- Situate the measuring cylinder and stand it carefully at the centre of the stand, so that it does not slip away. Extra care should be taken when dealing with the measuring cylinder such preventing it from breaking.
Table of results
Set 1, Experiment
Set 2, Experiment
Set 3, Experiment
Results from set 1, 2 and 3 have been averaged in the table below
Analysis and Conclusion
By observing the graph of results I can see that I have reached my desired trend, which is that as the temperature increases the viscosity decreases. To achieve this trend, I have ensured that the level of uncertainty in the measurements made were as small as possible. The radius of the sphere was measured as 5.25 × 10-3 cm. To measure this I used a micrometer which subdivided the main scale into 0.01mm and thus ensured full accuracy in the measurement. I have used a vernier calliper which is scaled into 0.1mm, to measure the radius of the measuring cylinder which measured as 1.8cm. When measuring the time it took for the sphere to descend, I reduced parallax by ensuring that all the readings were taken with my eyes level.
I have ensured my variables were controlled correctly by using the same sphere for each experiment that I have carried out. This ensured that the mass and the surface area of the sphere didn’t change throughout the experiment. I have carefully descended the sphere from the top surface of the syrup, making sure that it’s initial velocity is zero. In addition this process has ensured that the sphere travels at the same velocity, as it will be descended from the same position each time.
In order to maintain the volume of the syrup and to thus prevent any loss of it, I removed the sphere by holding the magnet on the outside of the measuring cylinder, instead of using my hands or anything else.
I have repeated the experiment thrice to make certain that I am obtaining similar values for viscosity at each temperature. I have achieved this simply by following the same procedure as I have done for the original experiment to make sure that nothing has been altered throughout the repeats. This would ensure that a reliable set of results are achieved at the end. For instance for experiments 1 and 2, at 450 the value of viscosity were the same, which was 3.71Nsm-2. This suggests the reliability of my repeated experiments. This is again proven at 400 where the values of viscosity are same at this temperature being 6.14Nsm-2, for experiment1 and experiment 3. Even for experiment 2 the value of viscosity only increased by 0.36 being 6.5 Nsm-2.
I have found an anomalous result on set 3, experiment. At 100, the value of viscosity is 658Nsm-2 whereas at 50 the value of the viscosity is only 535Nsm-2. This doesn’t fit into the general trend, which is that as the temperature decreases the value of viscosity increases. When looking back at the values, which I have used to calculate the viscosity, I can identify that the time taken for the sphere to descend at 50 was 418 seconds whilst at 100 was 514 seconds. Moreover at 100 for Experiment 1 the time it took was 298 seconds and for Experiment 2 the time took was only 290 seconds. This error could have been due to the difference in the way that I stopped the clock-watch. But the difference in the time that it took for the sphere to descend at 100 for experiment1 and experiment 3 is 216 seconds. This value is too big to be due to my carelessness. Therefore I think this was due to the variation of the sphere’s initial position of descend or due to the variation of the initial velocity at which the sphere travelled. To eliminate this fault in future, the sphere should be kept on a clamp and released from it. This would ensure that the sphere has a constant initial velocity throughout the experiment. Moreover it will ensure that the sphere is descending from the same position each time.
It was noticed that the temperature didn’t stay constant throughout each experiment. At 500, the time taken for the sphere to descend was only 1.5seconds and so the temperature wouldn’t vary by a big value in this small period. However at 50, the time taken for the sphere descend was 550 seconds, which is a long period. When I dropped the sphere it was 50 but when the sphere reached the bottom of the measuring cylinder the temperature was 80. This suggests the real value of viscosity at 50 will be higher than the result that I have obtained. As the temperature was increasing from 50 to 80 the velocity at which the sphere must have also increased which provides a smaller value of viscosity than the actual. I say this because when the temperature increases the syrup flows with ease, which causes the sphere to travel with a higher velocity. To eliminate this error a water bath can be used.
A water bath would maintain a constant temperature as the sphere travels from the beginning till the end, equilibrating the total temperature of the syrup. The measuring cylinder must be contained in a transparent beaker, to allow me to observe the descent of the sphere.
Sources and Reference
PHYSICS For Advanced Level
By, Jim Breithaupt
This book enabled me to understand the definition of viscosity and had widened my knowledge of viscosity by explaining how the properties of fluid link to the viscous of a fluid and how they function.
By, Keith Gibbs
I have found this book extremely useful since it has provided me the difference between laminar flow, turbulent flow and stream line.
A/LEVEL PHYSICS BOOK
This book has instructed me the forces that occurs when a sphere descend through the syrup.
From this web site I have found why the viscosity changes due to the change in the temperature, which helped me to provide the scientific evidence in my background knowledge as well as it has been very useful in my hypothesis.
This web page has introduced the Stokes law which was the relevant formula to calculate the viscosity of the fluid. Therefore I have found this web page very useful and helpful.
This web site has also helped me to understand the laminar flow theory in depth.