There are a number of things that were wrong with my experiment even though I achieved a good set of results. Firstly it was very difficult to take accurate readings with the equipment provided. In an ideal world I would have used light gates to acquire a more accurate reading of the time taken for that ball bearing to travel the 10cm as there will have been a degree of error in my readings due to reaction time between the line on the straw being submerged and my stopping of the stopwatch.
Light gates work using a laser, one side of the light gate transmits the laser and the other side is a receiver. This could be easily incorporated into my experiment, two light gates would be set up connected to a computer, one 5cm from the surface of the honey and the other 15cm from the surface of the honey. The transmitters would be on one side of the measuring cylinder and the receivers on the other, the honey is translucent and so the laser would pass through and could still be detected by the receiver.
When the Ball bearing is released it still has the 5cm time in which to reach terminal velocity, when it reaches the first light gate it will break the laser beam, the receiver ill no longer detect anything and send a message to the computer to start timing. When the ball bearing reaches the 2nd light gate 10cm later it will again break the beam, the receiver will not detect anything and will send a message to the computer so the timer will stop. All this would be far more accurate as the thinking time for a computer is far less than that of a human.
It would also mean that the exact moment that the ball bearing crossed the lasers would be recorded not 1 or 2 millimetres earlier or later like my results will have been. Another problem will have been inconsistency in temperature of the honey throughout the measuring cylinder, due to the glass of the measuring cylinder and the outside temperature being cooler that the honey, the honey on the outside of the measuring cylinder will have cooled far quicker than that in the centre causing viscous drag in the honey.
The speed of the honey at the wall will be zero and will be at its maximum in the centre, in the centre the honey will be much less viscose that that on the outside and so the cooler honey in the outer regions of the measuring cylinder will have less energy and not allow the ball bearing to pass through so easily slowing it down. This could be reduced significantly by keeping the measuring cylinder in a water bath of the desired temperature throughout the experiment so all the honey in the measuring cylinder is flowing at the same speed.
Vortices may also form as the ball bearing moves through the honey. As the vortices flow past the ball bearing energy transfers occur and heat is transferred from the honey to the ball bearing and the honey temperature drops. This in turn will increase the viscosity slowing the ball bearing down. In my experiment I did not take into account the effect of the bubbles in the honey if they have any effect at all. Even though in liquids, such as honey, the higher the temperature the lower the viscosity meaning the ball bearing falls faster in the warmer honey, gases are the opposite.
I have found out that in gases, the higher the temperature the more viscous they are and so any object moving through them will move slower in the warmer temperatures. This should not slow the ball bearing down however as gases are far less dense that the honey no matter what temperature and so when the ball bearing passed through the bubbles it would speed up slightly. This would give me inaccurate results for the viscosity of honey as the ball bearing will not have only passed through one medium but both the honey and the bubbles of air.
The amount of bubbles in the honey can be reduced but is a lengthy process. The honey must be left at least overnight to allow the bubbles to rise out. In the production of honey this process is called ‘ripening’ and works best when the honey is warm as the hotter the honey the less viscous it is and so the bubbles will be able to escape more easily and the ‘ripening’ will happen much more quickly than with cooler honey. When the straw was attached to the ball bearing the shape of the ball bearing was altered significantly, this is both due to the araldite and the straw itself.
The glue made small changes to the shape of the ball bearing meaning it was no longer spherical, this could also cause vortices (Eddys) to form lowering the temperature and slowing the ball bearing down. The straw itself will have also caused extra drag and will not have been perfectly cylindrical due to the soft flexible plastic it is made from again slowing the ball bearing down. This could be avoided by getting rid of the straw and the araldite. With the use of the light gates the straw would no longer be needed to aid the timing of the falling ball bearing.
If I were to use a strong magnet I would be able to ease the magnet up the inside of the measuring cylinder in order to remove it from the honey, this would be more time consuming and fiddly however would mean I could obtain a more accurate set of results. I did not take into account the density of the straw or araldite when calculating my coefficient of viscosity and so this would again make my results more accurate if the straw and araldite were removed from the experiment. The Use of Viscometers in the Food Industry [Chris Durling, General Manager, Research & Development, Aimia Foods]
The determination of material flow characteristics is vital in many areas of the food industry. Viscometers are common place, both in Quality Assurance/Control laboratories as well as R & D laboratories. Viscosity of food materials is crucial both for consumer acceptance e. g Tomato Ketchup and for process efficiency/consistency. Many food laboratories make use of simple relatively low cost viscometers or flow meters to provide a quick determination of viscosity or flow. Examples of these would be Elcometer’s Daniel Flow Gauge or Brookfield’s DV-E Digital Viscometer.
For thick liquids and paste e. g tomato ketchup, honey etc; a very simple Quality Control test can be performed. A known volume of material is poured into a reservoir and then allowed to flow for a known time over a graduated plate or trough. The reading is then expressed as the distance flowed. This relates to a products viscosity. Elcometer’s Daniel Flow Gauge – Material is poured into the channel and then the devise turned vertically, the product flowing onto the graduated plate.