1.2 Pressure

• define pressure and state its SI unit
• calculate pressure from force and area
• explain pressure in liquids and how it varies with depth
• relate atmospheric pressure to everyday observations

“Why does a sharp knife cut better than a blunt one?”

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1. What is pressure?
   40 min · 2 practice tasks · quiz
   Why the same push can feel gentle or painful depending on the area it acts over.
2. Pressure in liquids and gases
   40 min · 2 practice tasks · quiz
   Why pressure grows with depth, and why the atmosphere presses on everything.
3. Units of pressure and converting area
   40 min · 1 practice tasks · quiz
   Pascals need newtons and square metres, so centimetres must be converted before you divide.
4. Finding force or area from P = F / A
   40 min · 1 practice tasks · quiz
   Cover the quantity you want on the formula triangle: F = P x A and A = F / P.
5. Pressure in solids: sharp, blunt and pointed
   40 min · 1 practice tasks · quiz
   A small contact area turns an ordinary push into a cutting or piercing pressure.
6. Tyres, tracks and foundations
   40 min · 1 practice tasks · quiz
   Kenyan vehicles and buildings spread weight over a large area so they do not sink.
7. Deriving P = h rho g
   40 min · 1 practice tasks · quiz
   The pressure at the base of a liquid column is the weight of that column divided by its area.
8. What liquid pressure depends on
   40 min · 1 practice tasks · quiz
   Depth, density and g control liquid pressure; shape, volume and surface area do not.
9. Investigating how pressure changes with depth
   40 min · 1 practice tasks · quiz
   A tin with holes at three heights turns P = h rho g into a jet you can see.
10. Pressure at a point acts in all directions
    40 min · 1 practice tasks · quiz
    At one depth a liquid pushes equally up, down and sideways on a small surface.
11. Total pressure: atmosphere plus the liquid
    40 min · 1 practice tasks · quiz
    The absolute pressure at depth is atmospheric pressure plus h rho g.
12. Dams and water tanks in Kenya
    40 min · 1 practice tasks · quiz
    Dam walls are thickest at the base because pressure, and so force, grows with depth.
13. Pascal's principle
    40 min · 1 practice tasks · quiz
    A pressure change in an enclosed liquid is transmitted equally to every part of the liquid.
14. Hydraulic press and jack
    40 min · 1 practice tasks · quiz
    A small effort piston and a large load piston turn Pascal into a garage jack or a press.
15. Hydraulic brakes
    40 min · 1 practice tasks · quiz
    A foot on a small master cylinder sends equal pressure to larger slave cylinders at the wheels.
16. Atmospheric pressure around us
    40 min · 1 practice tasks · quiz
    Air has weight, so it presses with about 100 000 Pa at sea level on every surface.
17. The simple mercury barometer
    40 min · 1 practice tasks · quiz
    A 76 cm mercury column is the atmosphere weighed in a glass tube.
18. Fortin and aneroid barometers
    40 min · 1 practice tasks · quiz
    A Fortin barometer refines the mercury column; an aneroid uses a box, not a liquid.
19. Atmospheric pressure and altitude
    40 min · 1 practice tasks · quiz
    From Mombasa to Nairobi to Mount Kenya, the air column shortens and pressure falls.
20. The U-tube manometer
    40 min · 1 practice tasks · quiz
    A U-tube of liquid turns a pressure difference into a height you can measure with a ruler.
21. Measuring gas pressure with a manometer
    40 min · 1 practice tasks · quiz
    Worked examples of open and closed manometers, including the sign of h rho g.
22. Upthrust and Archimedes' principle
    40 min · 1 practice tasks · quiz
    A liquid pushes up on a submerged object with a force equal to the weight of fluid displaced.
23. Floating and sinking
    40 min · 1 practice tasks · quiz
    An object floats when upthrust can grow to equal its weight; that depends on density.
24. Siphons, pumps and the weather
    40 min · 1 practice tasks · quiz
    Atmospheric pressure drives siphons and lift pumps, and its changes are the weather map.
25. Pressure around Kenya: review
    40 min · 1 practice tasks · quiz
    Mix solids, liquids, the atmosphere and hydraulics in Kenyan settings, then check the whole sub-strand.