What Will Affect the Rate at Which Shapes Move Through Water?

Nim Joe Man Biology AT1

8 Green Mrs Booth

A general shape of fish, seals, sea lions etc. is roughly a teardrop or aerofoil shape (see diagram 1). My aim is to find out what will affect the rate at which different shapes move through water. I will do this by doing an experiment to see whether different shapes affect the speed that they move through water, based on the fact that a theory of evolution states that animals have evolved to suit their habitats/environments.

I think that my experiment should show that shapes with less surface area and shape tat are more aerodynamic would be quickest to travel through liquid. I think this because it has been proven that if a shape has more surface area then there will be more drag/resistance acting on it and its resultant speed would be slower than a shape with a smaller surface area (see diagram 2). I also think this because of evolution; during evolution I think that prey, like fish, have changed so that they can escape from predators and prevent themselves from being eaten while prey, like sharks, also change to be quicker so they can hunt and kill their prey more easily. So I think that the cube shape will be the slowest because it has the most surface area and that the tear shape and worm will be the quickest.

I will attain my aim by constructing an experiment that will involve different shapes in motion through a liquid. There are very little safety hazards but the usual laboratory rules apply. I will need to use the following:

Retort stand
Boss Head and clamp
Beaker with at least 200ml capacity
Long Glass Tube
Bung
Stopwatch
30g of plasticine
Weighing Scales
Funnel
160-180ml of wallpaper paste.

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Retort stand
Boss Head and clamp
Beaker with at least 200ml capacity
Long Glass Tube
Bung
Stopwatch
30g of plasticine
Weighing Scales
Funnel
160-180ml of wallpaper paste.

They will be set up as shown in diagram 3, with the clamp securely in the Boss Head and the Boss Head securely on the retort stand. Using the scales split the plasticine into six, 5g each, accurate to 0.01g. Then mould them into the following shapes: 1) A cone, 2) A tear drop, 3) A sphere, 4) A cube, 5) A spiral and 6) A long worm shape, making sure they stay the same mass (5g). The glass tube will be blocked at one end with a bung. Then I would pour the 180ml, accurate to the nearest ml, of wallpaper paste into a beaker than into the tube, using the funnel, and clamp to the retort stand. Wallpaper paste is used instead of water because water has hardly any resistance so you would need a tube as high as the ceiling, but I do not have these available resources so rather than lengthen the tube we will use wallpaper paste. The shapes will then be dropped, one at a time into the paste and timed for how long it takes to reach the bottom in seconds to the accuracy to 0.01seconds. The tube will then be unclamped and its contents poured into the beaker. Then it will be poured back into the tube using a funnel to save time and to separate the shape from the paste, and the drops repeated using the different shapes. There will be four times recorded for each shape and an average made.

The tube, the amount and properties of the paste, the mass of the shapes, the method of each drop, the dropping place and the timing; these will all be kept the same. The tube will be the same one throughout the experiment because if it was shorter it would take less time and if it were longer it would take longer anyway no matter what the shape is like. The amount of paste would be kept the same because if there were more paste there would be more resistance and further to travel therefore taking a longer time. The paste will be kept the same so that the thickness will be the same because if the paste is thicker then there will be more resistance and the shape will take longer to travel down the tube. The mass of the shapes will have to be the same because the point of the experiment is to find whether different shapes affect the speed of the shape in the paste. So if the mass is more then no matter what the shape is, it will sink faster because there is more mass so therefore more weight (bigger gravitational pull). The method of each drop would be kept the same because the only variable is the shape so if the method were different for each shape it wouldn’t be a fair test. I.e. the way the positioned for the drop. If the shape were put it one way for one drop but a different way for another drop then the times would be very different because there may be more surface area so that the shape will be slower. The shapes would have to be dropped at the same place, i.e. from the top of the tube rather than the top of the paste or 10cm on top of the tube. The timing will be kept the same meaning it will be timed from the time of letting go to the time it touches the bung on the bottom, rather than when it enters the paste and hits the bottom.

The independent variable will be the shape of the plasticine. This will be varied because it is the aim of the experiment, to find out whether different shapes affect the speed of motion in liquid so that has to be the independent variable.

I will try to make my results reliable by repeating the experiment a number of times and then averaging it and repeating results that do not fit in.

Please see graph that shows the average and the range of time taken for each shape to travel through the wall paper paste. Shaded area shows ranges and lined area shows height of average.

After looking at the results I conclude that the worm and tear shaped shapes moved the quickest through the paste, then the cone, then the sphere, then the spiral and the slowest was the cube shape. I find this from my results because the average results of the drops showed that on average the worm took 0.96, the tear shape took 1.68, the cone took 4.11, the spiral took 5.65, the sphere took 5.94 and that the cube took 10.46. This is explained by the fact that the worm and tear shape had less surface area and that the cube had the most (see diagram 4), as in my hypothesis and prediction above. My results match my prediction quite well in my view because I predicted that the cube would be slowest and it was, it was almost twice as slow as the next slowest shape. I also predicted that the worm and teardrop would be the fastest and they were more than twice as fast as the next fastest shape.

I think that the experiment was reasonably good way of testing the aim so I have some confidence that my results are able to be used compared with real nature but there could have been changes to make the results more reliable. The problems were the artificial conditions, which limited my confidence in the results. The problems were that the shapes were going vertically in the liquid but in nature most creatures go horizontally propelled by their own energy and by the moving current of the water and not by the force of gravity. The paste did not act as water would and was only used because of the property of water that meant there was very little resistance. The shapes were also simplified and shapes that aren’t usually seen in nature have been used in this experiment. I still think however that this is still linked to life. In life more streamlined shapes do actually travel faster than ones with a very big surface area but the artificial conditions made this point quite limited although being true. I think I would do an extension to this experiment. I would do this using water that flows of its own current horizontally as a first. Then the shapes would have to be shaped like proper animals and creatures. I think this would be done maybe in a stream to make it even more reliable and would be a very good extension to my experiment.