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Find the viscosity of water using a rigid glass tube (capillary). By further calculations, to find whether the flow of liquid is laminar or turbulent.

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Part 1 - Fluid Dynamics and Pressure Measurement Aim The aim of the investigation is to find the viscosity of water using a rigid glass tube (capillary). By further calculations, to find whether the flow of liquid is laminar or turbulent. Diagram Apparatus Uncertainty Water Beaker Funnel Rubber tubing Rigid glass tube (capillary) Basin Travelling Microscope +/- 0.0005cm Measuring Cylinder +/- 0.5cm3 Stop watch +/- 0.005s Ruler +/- 0.05cm 2 x Clamp stand Procedure The apparatus was set up as shown above. The length of the glass tube was taken and recorded, this was to stay constant. The height of the glass tube from the desk was measured as was the marker of water level on the funnel from the desk. The water was then poured into the funnel up to the marker point using the beaker and allowed to pass through into the basin. This was kept constant by a member of group who poured water into the funnel. The rate at which the water passed through at this particular height was measured. This was carried out by a member collecting water in the measuring cylinder, while another started the stop clock instantly. The clock was stopped as soon as the water reached 25 cm3 in the measuring cylinder. The volume here was kept constant, so that there were fewer errors in calculations. ...read more.


The volume was kept constant at 25cm3. % uncertainty = +/- 0.5 x 100 25 = +/- 2 % Stop watch This measured the time taken for the water to fill the measuring cylinder. The time was taken to a hundredth of a second. % uncertainty = +/- 0.005 x 100 25.93 = +/- 0.019 % Graph 1, drawn using Microsoft Excel, is shown on the next page. Graph 2, drawn by hand, on the page following graph 1. Gradient of the slope from Graph 1 Knowing Poiseuille's law as: Q = ? r4 x ?P 8?l A gradient of a linear slope is the division of the change in y by the change in x. Gradient, m = change in 'y' coordinate change in 'x' coordinate According to graph 1, the y- axis is the change in pressure and the x- axis is the change in flow rate. Gradient = ?P Q Therefore looking at Poiseuille's formula, and transposing it so that it equals the gradient, we have: ?P = 8?l = gradient Q ? r4 Therefore the gradient of the graph is 8?l also known as the resistance to flow. ? r4 Resistance to flow of a liquid can be characterised by the viscosity of the fluid if the flow of this fluid is smooth. ...read more.


Under normal conditions the flow of blood in the aorta is laminar, where v = 0.3ms-1. However, during heavy exercise the velocity can increase five times more and the flow becomes turbulent. Conclusion Carrying out this investigation, confirms Poiseuille's law for the viscosity of a fluid. It also proves how there are certain factors to be taken into account when using this formula. These factors include the pressure difference, the diameter/ radius of the tube and thus the flow rate of the fluid. There being this number of factors affecting Poiseuille's Law leaves room for error, as there has been in this investigation. Human error is quite significant and accounts for most of the anomalies that occurred. If there were more time, further precautions could have been taken to improve the investigation, and cut out certain sources of error. Studying Poiseuille's law, it is clear that there is this relation between the height, flow rate, pressure, radius and length. The radius and the length of the capillary were kept constant, though as the pressure increases; it would cause an increase in the viscosity. Also as the flow rate increased, it would cause a decrease in the viscosity. The flow was found to be laminar, though if there were more time to further the investigation there is a possibility the flow may have developed into turbulence. ...read more.

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