Coffee Straw Physics

1,395

Solution 1

Just to extend my comment about Capillary action which is the reason for the liquid rising through the capillary (straw in your case), I show this animation of how the diameter of the capillary (d) effects the height of the liquid (h) that rises above the contact surface.

The relation of $h$ and $d$ used to simulate this is taken from wiki page which is $$ h=\frac{4\gamma cos\theta}{\rho g d}$$

It is for water and with the value of all constants substituted we get $$h\approx \frac{2.96\times10^{-5}}{d}m$$

enter image description here

The diameter varies from $0.3mm$ to $2mm$

Also the answer to this question would make this true for your coffee as well.

Solution 2

You have 3 different materials in your experiment: a liquid (coffee, could be water), a solid (plastic straw) and a gas (air). You have interfaces between all three: liquid-air, liquid-solid and solid-air. In the case of the plastic of your straw, adhesion forces are stronger between plastic and water than plastic and air: so a force will tend to make the water spread on the plastic. This force balances with gravity to set the height of the capillary rise.

Solution 3

The liquid rises due to surface tension. In this case the adhesion between liquid and cup material Is higher than cohesion between liquid molecules. So it is higher than liquid in cup. I think the liquid in the straw that remains after removing will be lesser than the liquid that you saw rising while in the cup. Try for transparent liquids. The liquid in the case you mentioned is purely due to adhesion and not surface tension forces.

Share:
1,395
Taylor Lopez
Author by

Taylor Lopez

I am a Software Developer in beautiful Colorado with a wife (praise Jesus, how did that happen?!) and a cat. I love the problem-solving aspects of programming and the satisfaction that comes from developing a clean, clever, and efficient solution to a challenge. I have a bachelor's degree in Computer Science and a Mathematics minor from UCCS, and several years of professional programming experience. I find software development in a professional environment to be extremely fulfilling, especially when you can see the positive effects of something you have created. I desire to constantly be sharpening and honing my craft while expanding my knowledge with new technologies and languages; and I'm never opposed to constructive criticism if it means I grow from the experience (unless that constructive criticism involves where I put my curly braces). Languages I use (In order of strength) Javascript, JQuery, AngularJS Python 2&3 C# and the .NET framework C++ Java ActionScript 2 & 3 (Went through a HUGE Flash game dev phase) MySQL PHP VBA (ew) PowerShell Other things with which I'm pretty familiar HTML 4/5 CSS 3 XML JSON Hobbies Programming Developing utilities and games for fun. Maintaining my personal website. Video Games Any Japanese RPGs (my current fav is Square Enix's Bravely Default (I'm a huge sucker for a job system)) ALL THE POKEMON (recently completed my national Pokedex. Take that Markus Smithson from 2nd grade. Who's the master now!!!??!... Did I mention the miracle of me being married?) Music Guitar Singing Art Digital painting/sketching Web design Art Stuffs I used to do quite a bit of Digital Illustration and even some 2D animation for a while there, but not so much any more. When I was doing that stuff though, I was using: Adobe Flash CS5 Photoshop CS5 Adobe Illustrator CS5 Procreate (iOS application that runs MIND-BLOWINGLY well on a first gen iPad)

Updated on September 15, 2020

Comments

  • Taylor Lopez
    Taylor Lopez about 3 years

    When I put my little, cylindrical coffee straw into my coffee, the liquid immediately rises about half a centimeter up the straw without provocation. This is also the amount of coffee that the surface tension of the coffee will allow to stay in the straw when removed from the liquid in the cup.

    Keep in mind that all the while, the top end of the straw is open.

    Why does the level of the liquid in the straw insist on being higher than the level of all the liquid in the cup?

  • Taylor Lopez
    Taylor Lopez about 8 years
    Your answer confuses me. At first it sounds like you're saying "surface tension," but then you say "adhesion, not surface tension."
  • Taylor Lopez
    Taylor Lopez about 8 years
    I really like the simplicity of your answer. Thank you! +1