Pressure in Liquids and Gases
2 marks · NormalExplain, using the example of the Magdeburg hemispheres, how air pressure acts in all directions and what happens when the air is removed from inside the hemispheres.
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Air pressure acts in all directions, so when the air is inside and outside, the forces are balanced. When the air is removed from inside, only the outside atmospheric pressure acts on the hemispheres, making them very hard to pull apart.
Common mistakes: Ignores balancing internal pressure; Only mentions suction, not pressure
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Marking points
M1 · 1 mark · Mentions air pressure acts in all directions, balancing when present inside and out.
A1 · 1 mark · Explains that after removing air inside, only the outside pressure acts, causing hemispheres to stick.
Worked solution
Air pressure acts equally in all directions. When air is inside and outside the hemispheres, the pressures balance. Removing air from inside means only the outside atmospheric pressure pushes the two hemispheres together, so they cannot be pulled apart.