Help me by explaining these to me? Thanks.?

Question

Which one of the following depends on the atmosphere exerting pressure?

(1) A ball falling to the ground
(2) Drinking through a straw
(3) The spray from a can cola
(4) Bath water emptying down a plug hole

The answer is (2) Drinking through a straw...I don't understand why that is the answer instead of the other 3 alternatives..Could anyone please explain the reason to me on why drinking through a straw depends on the atmosphere exerting pressure? Hopefully you could also explain to me what the other 3 options depends on (instead of them depending on the atmosphere exerting pressure). Thanks.

Answer 1

No. 2 as you 'suck' on a straw, the pressure in the straw and your mouth decreases (slight vacuum).
The atmospheric pressure acting on the surface of the liquid in the can, is higher than that in the straw and your mouth. This pressure difference, pushes the drink into your mouth.

No.1. is due to the pull of gravity.
N0.3. is due to the higher pressure of the CO2 gas in the cola can. As you open the can, the gas pressure is released suddenly ('explosively') and, the gas leaving the liquid carries liquid with it as a spray.
No.4. The bath water, being at a higher elevation than the sewer (drain) pipe, again causes a pressure difference due to the height of the water above the sewer.
This causes the water to flow into the sewer from the bath.

Answer 2

Cheryl

In order for the fluid to move up the straw there has to be two things, atmosphere pushing down on the fluid and pressure in the straw less than atmospheric pressure

A ball will fall to the ground on the mood (no pressure)
the spray comes from the pressure in the can, and would spray in vacuum, (or in increased pressure if it was made on earth and carried to jupiter) the relative pressure would still be higher
Bath water going down a hole is again just gravity.
Hope that helps :)

Answer 3

I have to agree with you this question is tricky a and b obviously depend on gravity

but 2 AND 3 should depend on preasure
3. if the atmospheric preasure was high than the preasure in the can would be at equilibrium and thus would not spray.

2. depends more on the preasure you excert on it with your mouth in this case a lower preasure than the preasur outside

i dont think this is a very good question