Two metal hemispheres of radius 12 cm are put together, and the air inside is pumped out until…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Two metal hemispheres of radius are put together, and the air inside is pumped out until almost none is left. What force is needed to pull them apart? (Air .)
Need a reminder? The key ideaShow
The air presses with , the pressure of of mercury, at sea level. Gauge pressure is the pressure above the air's; absolute pressure includes it. An open manometer reads from the difference of its levels.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Area. .
Step 2. Force. .
Answer: About , the weight of nearly half a tonne.
Check. In 1654, two teams of horses could hardly pull such hemispheres apart.
Watch out. The force that matters is over the flat circle, not over the curved surface.
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