When food is stored in a container (a can or a jar), the food and the container

Question

When food is stored in a container (a can or a jar), the food and the container are heated to a very high temperature in order to kill the germs. Then the lid is attached. When the food and the container cools, the air pressure under the lid drops below Atmospheric Pressure, and the lid is pushed down by the weight of the air above it. This is why lids "pop up" when you open a sealed container. Suppose that a container of spaghetti sauce has a circular lid with a radius of 3.5 cm and that the air pressure underneath the lid is 38 kPa. How much force (in N) is required to lift the lid at sea level where the Earth's Atmospheric Pressure is 101.325 kPa.

Explanation / Answer

given,

air pressure underneath the lid = 38 kPa

Atmospheric Pressure = 101.325 kPa

pressure difference = 101.325 - 38

pressure difference = 63.325 kPa

radius = 3.5 cm

pressure = force / area

63.325 * 10^3 = force / (pi * (3.5 * 10^-2)^2)

force = 243.703 N

force required to open the lid = 243.703 N

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