funny bone

Are cats liquid? Answering this question won me an Ig Nobel

Ig Nobels rewards unconventional research that first makes you laugh and then makes you think, showing the world that science can be funny (and fun) too.

A liquid is traditionally defined as a material that adapts its shape to fit a container. Yet under certain conditions, cats seem to fit this definition.

Here a cat, whose body fits perfectly within a sink, behaves like a liquid. Photo credit: Sad and useless [Licensed under CC-BY]
Here a cat, whose body fits perfectly within a sink, behaves like a liquid. Photo credit: Sad and useless [Licensed under CC-BY]

This somewhat paradoxical observation emerged on the web a few years ago and joined the long list of internet memes involving our feline friends. When I first saw this question it made me laugh, and then think. I decided to reformulate it to illustrate some problems at the heart of rheology, the study of the deformations and flows of matter. My study on the rheology of cats won the 2017 Ig Nobel Prize in Physics.

The prizes are awarded every year by Improbable Research, an organisation devoted to science and humour. The goal is to highlight scientific studies that first make people laugh, then think. A ceremony is held every year at Harvard University.

What is a liquid?

At the centre of the definition of a liquid is an action: a material must be able to modify its form to fit within a container. The action must also have a characteristic duration. In rheology this is called the relaxation time. Determining if something is liquid depends on whether it’s observed over a time period that’s shorter or longer than the relaxation time.

Play

If we take cats as our example, the fact is that they can adapt their shape to their container if we give them enough time. Cats are thus liquid if we give them the time to become liquid. In rheology, the state of a material is not really a fixed property – what must be measured is the relaxation time. What is its value and on what does it depend? For example, does the relaxation time of a cat vary with its age? (In rheology we speak of thixotropy.)

Could the type of container be a factor? (In rheology this is studied in “wetting” problems.) Or does it vary with the cat’s degree of stress? (One speaks of “shear thickening” if the relaxation time increases with stress, or “shear thinning” if the opposite is true.) Of course, we mean stress in the mechanical sense rather than emotional, but the two meanings may overlap in some cases.

‘Deborah number’ and the flow of mountains

What cats show clearly is that determining the state of a material requires comparing two time periods: the relaxation time and the experimental time, which is the time elapsed since the onset of deformation initiated by the container. For instance, it may be the time elapsed since the cat stepped into a sink. Conventionally, one divides the relaxation time by the experimental time, and if the result is more than 1, the material is relatively solid; if the result is lower than 1, the material is relatively liquid.

This is referred to as the Deborah number, after the biblical priestess who remarked that on geological time scales (“before god”) even mountains flowed. On shorter time scales one can see glaciers progressively flowing down valleys.

Even if the relaxation time is very large (days, years), the behavior can be that of a liquid if the Deborah number is small (compared to 1). Conversely, even if the relaxation time is very small (milliseconds), the behavior can be that of a solid if the Deborah number is large (compared to 1). This is the case if one observes a water balloon at the instant when it’s popped.

The Deborah number is an example of dimensionless number: Since we divide one time period by another, the ratio does not have any unit. In rheology, and in science more generally, there are many dimensionless numbers that can be used to determine the state or regime of a material or system.

Measuring the flow of cake batter

For liquids there is another dimensionless number that can be used to estimate whether the flow will be turbulent, with vortices, or whether it will calmly follow the outline of the container (we say that the flow is laminar).

If the flow speed is V and the container has a typical size h perpendicular to the flow, then we can define the velocity gradient V/h. The inverse of this velocity gradient scales as a time.

Comparing this duration and the relaxation time produces the Reynolds number in the case of fluids dominated by inertia (like water), or the Weissenberg number for those dominated by elasticity (like cake batter). If these dimensionless numbers are large in comparison to 1, then the flow is likely to be turbulent. If they’re small in comparison to 1 the flow is likely to be laminar.

Asking the question of whether cats were a liquid allowed me to illustrate the use of these dimensionless numbers in rheology. I hope that it will make people laugh and then think.

Marc-Antoine Fardin, Chercheur en rhéologie, Université Paris Diderot – USPC.

This article first appeared on The Conversation.

We welcome your comments at letters@scroll.in.
Sponsored Content BY 

The perpetual millennial quest for self-expression just got another boost

Making adulting in the new millennium easier, one step at a time.

Having come of age in the Age of the Internet, millennials had a rocky start to self-expression. Indeed, the internet allowed us to personalise things in unprecedented fashion and we really rose to the occasion. The learning curve to a straightforward firstname.surname@___mail.com email address was a long one, routed through cringeworthy e-mail ids like coolgal1234@hotmail.com. You know you had one - making a personalised e-mail id was a rite of passage for millennials after all.

Declaring yourself to be cool, a star, a princess or a hunk boy was a given (for how else would the world know?!). Those with eclectic tastes (read: juvenile groupies) would flaunt their artistic preferences with an elitist flair. You could take for granted that bitbybeatlemania@hotmail.com and hpfan@yahoo.com would listen to Bollywood music or read Archie comics only in private. The emo kids, meanwhile, had to learn the hard way that employers probably don’t trust candidates with e-mail ids such as depressingdystopian@gmail.com.

Created using Imgflip
Created using Imgflip

And with chat rooms, early millennials had found a way to communicate, with...interesting results. The oldest crop of millennials (30+ year olds) learnt to deal with the realities of adolescent life hunched behind anonymous accounts, spewing their teenage hormone-laden angst, passion and idealism to other anonymous accounts. Skater_chick could hide her ineptitude for skating behind a convincing username and a skateboard-peddling red-haired avatar, and you could declare your fantasies of world domination, armed with the assurance that no one would take you seriously.

With the rise of blogging, millennial individualism found a way to express itself to millions of people across the world. The verbosity of ‘intellectual’ millennials even shone through in their blog URLs and names. GirlWhoTravels could now opine on her adventures on the road to those who actually cared about such things. The blogger behind scentofpetunia.blogspot.com could choose to totally ignore petunias and no one would question why. It’s a tradition still being staunchly upheld on Tumblr. You’re not really a Tumblr(er?) if you haven’t been inspired to test your creative limits while crafting your blog URL. Fantasy literature and anime fandoms to pop-culture fanatics and pizza lovers- it’s where people of all leanings go to let their alter ego thrive.

Created using Imgflip
Created using Imgflip

Then of course social media became the new front of self-expression on the Internet. Back when social media was too much of a millennial thing for anyone to meddle with, avatars and usernames were a window into your personality and fantasies. Suddenly, it was cool to post emo quotes of Meredith Grey on Facebook and update the world on the picturesque breakfast you had (or not). Twitter upped the pressure by limiting expression to 140 characters (now 280-have you heard?) and the brevity translated to the Twitter handles as well. The trend of sarcasm-and-wit-laden handles is still alive well and has only gotten more sophisticated with time. The blogging platform Medium makes the best of Twitter intellect in longform. It’s here that even businesses have cool account names!

Self-expression on the Internet and the millennials’ love for the personalised and customised has indeed seen an interesting trajectory. Most millennial adolescents of yore though are now grownups, navigating an adulting crisis of mammoth proportions. How to wake up in time for classes, how to keep the boss happy, how to keep from going broke every month, how to deal with the new F-word – Finances! Don’t judge, finances can be stressful at the beginning of a career. Forget investments, loans and debts, even matters of simple money transactions are riddled with scary terms like beneficiaries, NEFT, IMPS, RTGS and more. Then there’s the quadruple checking to make sure you input the correct card, IFSC or account number. If this wasn’t stressful enough, there’s the long wait while the cheque is cleared or the fund transfer is credited. Doesn’t it make you wish there was a simpler way to deal with it all? If life could just be like…

Created using Imgflip
Created using Imgflip

Lo and behold, millennial prayers have been heard! Airtel Payments Bank, India’s first, has now integrated UPI on its digital platform, making banking over the phone easier than ever. Airtel Payments Bank UPI, or Unified Payment Interface, allows you to transfer funds and shop and pay bills instantly to anyone any time without the hassles of inputting any bank details – all through a unique Virtual Payment Address. In true millennial fashion, you can even create your own personalised UPI ID or Virtual Payment Address (VPA) with your name or number- like rhea@airtel or 9990011122@airtel. It’s the smartest, easiest and coolest way to pay, frankly, because you’re going to be the first person to actually make instant, costless payments, rather than claiming to do that and making people wait for hours.

To make life even simpler, with the My Airtel app, you can make digital payments both online and offline (using the Scan and Pay feature that uses a UPI QR code). Imagine, no more running to the ATM at the last minute when you accidentally opt for COD or don’t have exact change to pay for a cab or coffee! Opening an account takes less than three minutes and remembering your VPA requires you to literally remember your own name. Get started with a more customised banking experience here.

This article was produced by the Scroll marketing team on behalf of Airtel Payments Bank and not by the Scroll editorial team.