DC Physics logo

February 23, 1583: Birthday of Jean-Baptiste Morin more: Today in Physics  

HOME


space

 

 

Part 1: Walking with Coffee

May 2003

The Problem...

Same old story, it could any professor, in any Physics department, at any University... Dr. Jones is running late again. Whoever thought up Monday morning 8:00 lectures anyhow? He grabs the essential supplies: notes, marked assignments, coffee... and rushes down the hall. His desire to stay in the custodians' good books is slowing him down. Run two steps then WHOOPS - watch that coffee! Run another two steps, WHOOPS again. He is so busy trying not to spill while he hurries on that he doesn't even wonder whether the coffee oscillations are low enough amplitude to be Simple Harmonic Motion, or whether these vibrations might be Bessel functions, or whether his walking speed is in resonance with the frequency of the oscillation. Nope, he isn't thinking like a Physicist at all!!! Suddenly he realizes he is about to collide with Dr. Smith, so he comes to an abrupt stop... but of course the coffee doesn't. Seeing the forward momentum of the coffee is about to cause some to flow over the edge onto Dr. Smith he reflexively pulls back. Now the coffee has an even higher forward velocity relative to the cup and a generous amount sloshes onto Dr. Smith. Now Dr. Jones has another problem - the cup of coffee radidly traveling towards his own body. Again his reflexes kick in and he pushes the cup away, reversing the last process and sloshing coffee onto himself as well. He apologizes to Dr. Smith and they head back to the coffee room to find a towel.

Eventually Dr. Jones arrive to teach his class. He is late, somewhat disoriented, and embarrassed about the coffee stains on his shirt. So he apologizes to the class:
"I'm very sorry to appear so late and looking like this, but Dr. Smith and I got sloshed on the way to class this morning."

Next thing you know the local papers are running articles on drunken professors...

Ok, so that never happened, and probably nothing remotely like that ever happened. However, it does introduce something I'll be discussing in a couple of these monthly features - the great unsolved mystery of the best way to walk while holding a cup of coffee.

The Solution?

"Put a lid on it?" That's what people tell me when I pose the question, but somehow I don't think they're talking about the coffee cup. Sure there are times when the trivial solution can be applied, but what's the fun in that? Besides, a lot of the time lids aren't available or the person is using a mug which cannot take a lid.

As far as I can recall, my brother Rob is the only person I know who has seriously taken up this question. In fact, I think he is more serious about it than me (and you can see how serious I am). A little while ago he sent me a proposed solution by email, a method of moving the cup while you walk that should serve to damp the oscillations. Intriguing, but I haven't had time to study it yet. So, I'm leaving it at that for this month. I've posed the question and will be curious to see if anybody sends me their own thoughts. In Part 2 I'll be presenting my own thoughts on the matter, my brother's proposal, and anything else of interest that comes to me between now and then.

DC Physics Home Page | More DC Physics Notes