Fate of the Milkshake

Classical Mechanics Level 1

Suppose you are drinking some milkshake from a straw.You start sucking it but bite the straw before it's fully filled and lift it out the glass.

What happens next ?

The level of milkshake in the straw Rises The straw gets Emptied The level of milkshake in the straw remains Same

3 solutions

Parth Sankhe
Jan 7, 2019

There is a column of air between the milk and the bite point of the straw. If the milk runs down, this will create a vacuum in that region, which thus exerts a force on the milk to keep it in equilibrium.

The milk will also not run up the straw, as this will require some external force to compress that air column. There is no such external force.

I can't understand how running of milk down creates a vaccum there

V i S i o N . - 2 years, 5 months ago

If milk runs down, Space will be created between bite point and milk, but the same amount air will have to fill that space up. As we know, at same temperature and amount, as volume increases pressure decreases. Hence this pressure would be lesser than the atmospheric pressure (which the bottom of the milk column is exposed to). This would put a net upward force on the milk.

Parth Sankhe - 2 years, 5 months ago

Shubham Singhal
Feb 10, 2019

Maybe I can help you

Pressure difference between upper and lower side of the milk column is rho g h

. I.E. Weight of the milk column divided by its area

then net force will be acting upwards i.e. pressure*area I.e. Weight of the milk column

Thus force of gravity is cancelled and milk column remains intact. 😬😬😬😬😬😬😬😬😬😬😬

Stepan Nazarov
Jan 7, 2019

You can check it by doing so in real life :)

I did and then asked but i am not satisfied by the explanations on the internet

V i S i o N . - 2 years, 5 months ago

good idea and question

Stone Y - 2 years, 2 months ago

Fate of the Milkshake

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