Physics
Fluid Dynamics
3,560 words, 10 sections. The first two are free.
The opening sections
Definitions first, then the reasoning. Each section is short enough to read in one sitting.
This chapter is Physics unit 5, Fluid Dynamics, of the PMDC MDCAT-2025 uniform curriculum, inside Physics, which carries 36 of the 180 marks in the paper. It has been asked 97 times across 43 official papers between 2003 and 2026. The weight splits almost evenly in two, with the equation of continuity and Bernoulli's principle carrying 45 distinct questions between 2006 and 2026 and fluid flow and viscosity another 45 between 2003 and 2026, buoyancy a distant third at 7. A student who has mastered the chapter can follow one stream through a pipe that narrows and widens, reach for the right conservation law when a pressure question is put, and derive a terminal velocity from Stokes' law without losing the thread.
An ideal fluid satisfies three conditions at once: incompressible, so its density does not change; non-viscous, so its layers slide past one another without internal friction; and in steady flow. Every equation in this chapter is a promise made under those conditions, and the conditions are the examinable part.
Steady flow, also called streamline or laminar flow, means the pattern does not change with time: every particle passing a point follows the same path as those before it, and that path is a streamline. Streamlines cannot cross, since a particle arriving at a crossing would have to choose two directions at once. Friction with a wall slows the boundary layer, so the fluid touching a vessel is slowest, though still moving, while the centre is fastest. Incompressible means constant density, not the inability to move; non-viscous means no internal friction, not no pressure.
8 more sections in this chapter
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