Atmospheric pressure

• How is the suction cup is able to support weight?

  Air is pushed out from inside of the suction cup, hence holding it against the surface.
• how are the eggs in the carton are able to withstand the weight without cracking

  large area in contact between the eggs and the feet . less pressure exerted on the eggs, hence it does not crack.
• Why does the suction cup does not work on a dirty surface

  Dirt may cause gaps which allows air to enter the suction cup. There may be no difference in air pressure, causing the cup to drop.
• The difference in air pressure within & outside the suction cup in order for it to work:

  Air pressure outside the suction cup is higher than the air pressure inside the suction cup.
• changes in air pressure when drinking

  The air pressure in the cup is lower and becomes lower than the surrounding atmospheric pressure so all air particles are removed from the drink
• if there is a hole in the straw, liquid cannot be sucked out, why?

  Air pressure inside the straw is the same as the atmospheric pressure , therefore there is no difference of pressure to force the liquid up the straw.