PHysics!!!!!!?

Question

Explain:
a)why it is difficult to remove the lid from a preserving jar which was close then the space above the food was full of steam.
b)why evaporated milk flows out of the can more easily if two holes are made at opposite sides of the can top.
c)why diving bells (diving apparatus for underwater work which has an open bottomand is supplied with compressed air) for exploring deep sea water are built in a spherical shape.
d)why the water storage tank is in the roof of your house

Answer 1

a) when steam was present the temperature of the air beneath the lid was 100 degrees celsius and the pressure was high. When the steam cooled down the pressure was reduced causing the formation of a vacuum inside the container. The air outside the container pushes on the lid inward making it hard to open. Also, after the steam cooled down the lid also cooled down and contracted (becuase it is made of metal it contracted quite a bit), this causes the lid to be more firmly closed.

b) air pressure acting on the milk through one of the holes pushes the milk outside through the other. If there is only one hole a sort of disturbed vortex flow is created becuase at first milk is evacuated, but air must rush into the container to take its place (pressure must be equalised outside and inside of the container)

c) The pressure of the water in the depths of the ocean is tremendous. For each 10 meters of water you decend the pressure raises by 1 atmosphere (or 100,000 pascals). A spherical shape has the smallest amount of surface to volume ratio and so the force acting on a spherical diving bell at large depths is the smallest force possible from all shapes that contain the same amount of volume, this allows the bell to withstand deeper depths or conversly larger pressures.

d) Water will always move from a higher potential to a lower potential with out an external force acting on it (except from gravity), i.e. from a high point to a low point. If you place a water tank on the roof you do not need a pump to move the water from the tank to your faucet.

Answer 2

a. When steam cools to water vaper, the pressure drops, creating a vacuum. This makes opening the lid harder.

b. If you only put one hole in the can, as the milk is poured, the volume once occupied by the poured milk, mostly air, is reduced in pressure since the volume increased, creating a vacuum. The flow of milk is hindered by the vacuum. Putting a second hole in allows air to flow into the volume once occupied with the poured milk.

c. A sphere evenly distributes water pressure over the surface of the sphere. Any other shape will have uneven forces on it resulting in the need to overbuild the bell or bell collapse.

d. Water tanks are elevated to use the force of gravity to get higher water pressure.

Hope this helps!

Answer 3

a) Steam filled the space. Steam condensed. Space not full. Therefore, partial vacumn. b) Second hole allows air to enter and replace the exiting milk... thereby preventing a partial vacumn. c) If the bottom is open, it's not for strength. I don't know. d) Gravity provides water pressure at the faucets, etc., below - approx. 1/2 pound of pressure for each foot of vertical separation.