Why Does It Take More Suction to Drink a Can With 1 Straw?

[PhysicsN00b]

Hi, I was wondering if anyone can tell me the reason why do we need to suck harder to drink a can drink when 1 straw is out of the drink and 1 straw is in the drink than when we suck the 2 straws while the 2 strws is in the drink?

Sorry For the bad english... I'm from asia you see...

 

[arunbg]

What do you mean harder ? I have never had such an experience

 

[turbo]

If one straw is out of the drink, you are losing the negative pressure (relative vacuum) in your mouth because of leakage through that straw and you will have to work harder to get a given amount of fluid up through the straw that is submeged. If both straws are in the liquid, a modest amount of effort will get your drink to your mouth in sufficient quantities, because without the air leakage, you will be more easily able to generate the vacuum necessary to draw the fluid up the straws.

 

[andrevdh]

Drinking through a straw is accomplished by reducing the pressure on top of the liquid in the straw by sucking on it (removing some of the gas). The higher atmospheric pressure on top of the liquid in the can then pushes the liquid upwards in the straw. This is somewhat similar to pressurized spray cans, except that the pressure in the can is higher than atmospheric pressure forcing the contents out when the valve is opened.