About the SA Blog Network

The Scicurious Brain

The Scicurious Brain

The Good, Bad, and Weird in Physiology and Neuroscience
The Scicurious Brain Home

IgNobel Prize Winner in Fluid Dynamics: ARGH! I spilled my coffee in the hall again!

The views expressed are those of the author and are not necessarily those of Scientific American.

Email   PrintPrint

We’ve all been there. You’re heading in to work or to that meeting or down the hall with you coffee, and it NEVER fails. Splish splash and you’re leaving a little trail of coffee dots in the hall so everyone will know where you’ve been. We put lids on our coffee cups and even those sometimes fail (I swear every fourth one at Starbucks does), causing the little drips to get all over your hand. Even when you shuffle along with your coffee, trying hard not to spill it, the sloshing is imminent, and you can feel it waiting, waiting to spill your precious coffee, the only hope you had of making it through that morning alive.

But what causes coffee to spill like that when you walk? Why can’t it just rock gently back and forth? To study this, we need a hero. A hero of FLUID DYNAMICS.

Presenting the Ignobel prize in fluid dynamics.


Mayer and Krechetnikov. “Walking with coffee: why does it spill?” Physical review, 2012.

When I met Krechetnikov at the Ignobels and asked about where the study came from, he said he got the idea at a conference. While many ideas have been hatched at conferences during deep discussions or casual chat between scientists, this one was during the coffee break. Specifically Krechetnikov and his graduate student were watching other people at the coffee break, and watching them shuffle around as they tried desperately not to spill their coffee. And they got to wondering why, exactly, coffee behaves that way in a cup when you walk.

Luckily for them, they were both researchers in fluid dynamics.

So they got high speed video, some brave volunteers, and a cup of coffee (well, probably more than one cup of coffee was harmed in the making of this paper). The cup of coffee was equipped with spill sensors and with sensors to detect the movement of the coffee. The participants walked at various paces, either focused on not spilling the coffee, or not focused and just walking.

What the analysis of the videos showed was three competing motions of the coffee in the cup. The side to side sloshing,the forward-back sloshing, and the up and down motion of the walking. This ends up producing the motion of coffee that ends up swirling around in the cup, as well as rising up and down, resulting in spills.

Here you can see the oscillations involved, with the red line at the point of spill.

So how do we build up those oscillations? It depends, not on how FAST we are walking, but how quickly we get to that speed. In other words, on the acceleration. If you start to move more quickly, you will spill quickly, and if you accelerate slowly, you will spill less. In addition, when you focus on NOT spilling, you walk slower. But once you stop accelerating and are walking at a constant pace, you get a natural frequency of excitation and are less likely to spill.

So first your acceleration sets the “initial sloshing amplitude”. This gets amplified by the rocking motion of your walk. Noise of moving side to side, moving your arm, etc, adds to the sloshing and generates a swirl in the cup. And of course, there is your pace, and there is the coffee level. A less full cup will still slosh, but will not reach heights high enough to spill.

When it comes to how to control the slosh, the authors suggest coffee cups that have more give in the walls, allowing them to act to absorb sloshes (though that might present shape problems that would make it hard to carry), and hypothesize that concentric rings inside the coffee cup might help break up the oscillations. But when I asked, Krechetnikov admitted that the best way was probably to use a lid, and maybe fill your coffee cup a little less.

*Sci would like to note that she had to stop in the middle of writing this, get up, and make some coffee. Because otherwise it was just WRONG.

Scicurious About the Author: Scicurious is a PhD in Physiology, and is currently a postdoc in biomedical research. She loves the brain. And so should you. Follow on Twitter @Scicurious.

The views expressed are those of the author and are not necessarily those of Scientific American.

Rights & Permissions

Comments 9 Comments

Add Comment
  1. 1. Derick in TO 10:47 am 09/28/2012

    Great study! Now all they need to do is figure out how to stop the coffee from dripping out from under the lid. At least a couple of times a week I’m washing my hands in coffee as it drips and dribbles down the side of a fully-covered cup while I walk to work from the coffee shop. Conference-style lid or standard, makes no difference I can tell.
    Forget space elevators, FTL or practical human immortality – help us figure out how to keep our coffee in the cup!

    Link to this
  2. 2. 54EchoKen 11:09 am 09/28/2012

    I have found that if I hold my cup piched at the rim with two fingers the cups inertia helps to stabilize it from excess movement.

    Link to this
  3. 3. jctyler 12:11 pm 09/28/2012

    a) anyone ever worked in a pub to finance his studies knows that your platter should not move in rythm with your steps else the liquid works itself into a splatter;

    b) what is it today that everybody gets a cup and starts walking? get a cup and SIT down.

    This study’s real worth is that it proves some people to get too many grants to waste too much time which they then recover by running with a cup to their desks. WTH?

    I have one good cup of coffee a day. I sit down, I drink it while I read the paper. The other two or three are espressos, real espressos, not the concentrated garbage with funny tattoos from some corporate mass brewer.

    THIS is a coffeehouse and THESE are coffees:,ctr:countryDE&prmd=imvnse&tbm=isch&tbo=u&source=univ&sa=X&ei=WcllUNO5NoWShgfFnoHoDw&ved=0CEoQsAQ&biw=1168&bih=588

    THESE are espresssos:,or.r_gc.r_pw.r_qf.&biw=1168&bih=588&wrapid=tljp134884863211902&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&ei=9stlUOKoL8_Lsgb3q4GAAg#um=1&hl=en&rlz=1R2GGHP_en-GBLU423&tbm=isch&sa=1&q=espresso&oq=espresso&gs_l=img.3..0l10.2114.5332.0.5672.…0.0…1c.1.kfGm13_OEgo&bav=on.2,or.r_gc.r_pw.r_qf.&fp=957d702253ac3cf&biw=1168&bih=588

    These are morons with hot black water:…3177.3177.0.4346.…0.0…1ac.1.FknDlPiW9HY

    Link to this
  4. 4. jctyler 12:14 pm 09/28/2012

    What I especially mind about morons walking with one-way coffeecups is the environmental waste. It’s HUGE.

    Make my day, bump into a moron and make him spill his garbage over himself.

    Link to this
  5. 5. scicurious 12:17 pm 09/28/2012

    Little bitter today jctyler?

    Link to this
  6. 6. jctyler 12:37 pm 09/28/2012

    nope, only my espresso

    but someone has to stand up for quality or else starplonk becomes a standard

    (your article is very fine BTW as usual; and the study on the physics involved is amusing; had it been done on tea I probably wouldn’t even have minded but I’m partial to the quality of my coffee which I see sullied by the fast food industry and c-movie actors trying to look cool)

    Link to this
  7. 7. jctyler 12:41 pm 09/28/2012

    also, I keep forgetting that only comments on editorial articles accept less-than/greater-than signs but blog articles don’t.

    take it with a drop of red wine (or a tiny piece of chocolate) in your espresso “g”

    Link to this
  8. 8. jctyler 12:49 pm 09/28/2012

    - What I especially mind about morons walking with one-way coffeecups is the environmental waste. It’s HUGE.

    - Make my day, bump into a moron and make him spill his garbage over himself “g”

    - nope, only my espresso “g”

    does to a comment what white china does to a coffee, makes it taste better, no?

    Link to this
  9. 9. StrongHoldInc 3:06 am 06/4/2014

    Love this! Nice work.

    Check out the Sip-Tube, aka Spillinator. It prevents all spill and splash from lids.

    Link to this

Add a Comment
You must sign in or register as a member to submit a comment.

More from Scientific American

Email this Article