Pressure and depth
2 marks · NormalExplain, using ideas about forces, why the pressure at the bottom of a swimming pool is greater than the pressure at the surface.
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There is more water above the bottom, so the weight of water increases with depth, increasing the force per unit area (pressure).
Also accept: Pressure at the bottom comes from the weight of all water above
Common mistakes: Describing pressure as just depth without mention of force or weight
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Marking points
B1 · 1 mark · Mentions weight/force of water above increases with depth
B2 · 1 mark · Correctly links force per unit area to increased pressure at greater depth
Worked solution
At the bottom there is a greater weight of water above, causing a larger force on the area. Pressure is force per unit area, so this results in higher pressure at the bottom.