What causes a vacuum?
 Fred |
 Lilly |
„
Ok: so in the beginning the jar is hot and there is also hot air inside it. The the lid is put on. The jar and the air within it cool down and...
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a) the pressure in the jar decreases.
b) the pressure in the jar increases.
a) the pressure in the jar decreases.
b) the pressure in the jar increases.
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Right. The air pressure outside the jar however hasn´t changed. Now we should compare the pressures inside and outside the jar.
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„
So when the jar was still open the pressure inside and outside of it were equal. The moment the lid came on the same force acted on the top and bottom side of the lid.
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