- In I/GCSE Physics, LAMINAR – (streamline) occurs a lower speeds, and changes to
- TURBULENT – as the fluid velocity increases past a certain value
- This changeover velocity will vary depending on the fluid in question and the shape of the area through which it is flowing
If water is flowing through a pipe slowly, it is LAMINAR flow. Look at the laminar diagram, the arrows closest to the edge of the pipe are shorter than the rest due to friction, meaning this layer moves slower than the other ‘layers’. The next ‘layer’ will experience friction from the outermost one, and so on until we get to the middle layer. Each layer closest to the centre will experience less friction, thus allowing it to move faster. The inner-most layer moves the fastest, as
THE VELOCITY INCREASES THE NEARER YOU GET TO THE CENTRE
If a liquid follows Newton’s formulae for the frictional force between the layers in streamline flow, then is known as a NEWTONIAN LIQUID
- Laminar flow – in the same place within the fluid, the velocity of the flow is CONSTANT over time.
- The lines of laminar flow are called STREAMLINES, at any point on any of these streamlines; the velocity of the flow will be constant over time.
- In turbulent flow, the fluid velocity in any given place CHANGES over time. The flow becomes chaotic and eddies form, causing unpredictable higher and lower pressure areas. Turbulent flow increases the drag on a vehicle and so increases fuel consumption
- Streamline flow produces much less air resistance than turbulent. Thus by altering the aerodynamics of their suits, skiers can raise the velocity at which the air movement past their body will change from laminar flow to turbulent flow. This is the principle behind all ‘streamline’ designs, such as sports cars and boats
In I/GCSE Physics, VISCOUS DRAG (the friction against you) is greater in water than in air. The frictional force is due to the fluids viscosity.
Low viscosity = low frictional force (e.g. air)
High viscosity = high frictional force (e.g. treacle)
- Newton developed a formula for the friction in liquids which includes several factors, one of which is THE LIQUID.
- The fluid-dependent factor is called the coefficient of viscosity.
- The rate of flow of a fluid flowing through a pipe is inversely proportional to the viscosity
- of the fluid.
- In industry, the rate of flow of liquid chocolate through pipes in the manufacture of sweets will vary with the chocolates viscosity.
- In I/GCSE Physics, TEMPERATURE also affects viscosity. In general, liquids have a lower coefficient of viscosity at higher temperature. For gases, viscosity increases with temperature.
That's all~ Thanks for watching.