Pressure in liquids and the atmosphere
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 2 worked examples, 5 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Why your ears hurt in the deep end
- Pressure in a liquid
- Pressure grows with depth
- The equation
Read the transcript of the teaching part
Last time
Before we start: last time, in Pressure, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Why your ears hurt in the deep end
Dive to the bottom of a swimming pool and your ears begin to hurt. The deeper you go, the bigger the pressure of the water on you. And above us there is another sea, the air, which also presses on everything. Today we measure both.
Pressure in a liquid
A liquid presses on the bottom and on the sides of its container, and on anything inside it. At any one point, the pressure acts equally in all directions. The deeper you go, the greater the pressure, because there is more liquid above. A denser liquid gives a greater pressure at the same depth.
Pressure grows with depth
This tank shows the pressure arrows getting longer with depth. At a depth of one point two metres in water, the pressure from the liquid is twelve thousand pascals. The arrows point in all directions, not only downwards.
The equation
The pressure caused by a liquid is its density times g times the depth. Here ρ is the density in kilograms per cubic metre, and g is ten newtons per kilogram. And h is the depth below the surface in metres. It is the vertical depth, not the length of a pipe. The answer is in pascals. The shape of the container does not matter.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Atmospheric pressure · Pressure in liquids · Pressure in liquids.
Chapter 1.8: Pressure
- Pressure = force ÷ area 6 min
- Pressure in liquids and the atmosphere 6 min
Also for O Level Physics 5054
Which topics come up most in O Level Physics 5054 past papers, counted from every paper since 2004.