Return Home

A Recipe for Perpetual Motion?

Wednesday, December 01, 2010 - 03:39 PM

A cat and a piece of jellied toast: could you break the laws of physics with these two simple tools? Check out this week’s podcast, Gravitational Anarchy, and be sure to listen for Neil deGrasse Tyson’s explanation of one of the more elegant and DIY paradoxes out there.


More in:

Comments [25]


One thing I will say, is that it's nothing to do with the cat having enough time to properly land feet-first... They can do that in a millisecond. seriously.

Dec. 18 2010 11:35 AM
Hamish from Melbourne, Australia

Cat jumps from 30ft power pole, no splat:

Dec. 13 2010 09:05 PM
Filipe from Brooklyn

This reminded me of an Oscar winning short film from 2003, by Kimberley Miner, called Perpetual Motion:

Dec. 13 2010 09:59 AM
Soppy Hen from Washington, DC

My memory is fuzzy but I think John Allen Paulos addresses the seeming paradox re falling cats in his book, A Mathematician Reads the Newspaper. Basically, yes, that--within limits--cats do better when falling from higher distances than lower distances because it gives them enough time to twist themselves and land feet first.

Dec. 12 2010 01:18 PM
Joanna from Baltimore, MD

Eric T., I remember the same documentary you're talking about. And what the video showed is what Barbara from New Salem, MA describes. Cats seem to instinctively rotate themselves while falling, and the longer falls gave them more time to successfully complete this maneuver. I'm surprised this particular angle wasn't touched on at all in the podcast.

Dec. 10 2010 05:15 PM
Eric T.

My memory may be fuzzy, but I'm pretty sure there was a documentary shown on PBS (maybe Nova?) back in the late 80's/early 90's that was at least partly about this cat falling from high stories phenomenon. I'm almost positive it at least mentioned the Manhattan vet research paper. But what I really remember is that it had high speed film (shown at normal/slow mo-speeds) of cats falling from various heights where you could see the cat react at various distances from being dropped.

My PBS search-fu was weak to find such film though.

Dec. 10 2010 03:56 PM
Ethan Bernard from New Haven, CT

Dr. Tyson-
Is the sensation of floating on water the same as that of weightlessness in orbit? It is certainly not. When you are weightless in orbit you experience only the force of gravity, which accelerates all of the particles in your body downward equally and is therefore imperceptible. When you float on water you are subject to the same imperceptible gravitational force acting downward plus an equal and opposite force from the water below you pushing upward. You can feel the force from the water because it only pushes on your skin.
Cats at low velocity have little wind resistance and should perceive no forces at all, just like astronauts in orbit, whereas cats at terminal velocity should experience an upward force equal to their weight on their skin from the wind resistance, just like someone floating in water. Of course there will be lots of buffeting from the wind that isn't present when floating on water--one of many reasons why it is hard to believe the cat will relax.

- a physicist

Dec. 09 2010 07:08 PM

Love Tyson, but he never went skydiving. The tingle you get in the pit of your stomach on a roll-y-coaster goes away when you hit terminal velocity. Tingle gone--cat relaxes--better outcome.

Dec. 09 2010 11:05 AM
Coby Smolens

I am a great N dG Tyson fan, love his work, his approach to the public understanding of Science - and he's got it wrong this time. While he is correct in saying that the sensation of weightlessness would be nearly instantaneous for the cat as it began its fall, the sensation of acceleration due to wind resistance would increase until terminal velocity was acheived, at which point (actually not a point but a bell curve) the sensation would taper off as wind speed maxed out.This might be empirically testable by monitoring physiological responses in humans (a little turning of the tables?) jumping out of airplanes. Probably need to do this with novices, to approximate the responses of cats - unless these cats are veteran building jumpers...

Dec. 09 2010 09:55 AM
Zeb from Seattle

Scott is completely right. I don't know exactly what in the world Tyson was thinking, but he was largely incorrect in this one.
When the cat was falling, it's sensation of its weight would be constantly changing as it was accelerating-- which likely would stop it from relaxing. As soon as it hits zero acceleration (terminal velocity) then it's perceived weight will stay the same (normal weight), which will probably cause it to relax. To say that it's sensation of its own weight doesn't change throughout the fall is utterly false. Your perceived weight is the amount of resistance you are getting as you try to go downwards. If you are accelerating, that is, your speed is rising, the resistance you receive will rise as well. Therefore, if you are ever accelerating, your perceived weight will be on the rise.
However, as soon as you stop accelerating (also known as terminal velocity) then the resistance will be the same. This will cause you to feel that you are the same weight. I would not be surprised if it was indeed true that this caused a cat's muscles to relax.
I know a lot about physics, but we need to bring in a studier of feline anatomy to verify if this relaxation would indeed decrease injuries.

By the way, does everyone think this post is pretty good? I'm kinda nervous I'm going to say something stupid because I am only in middle school.

Dec. 09 2010 01:39 AM
Happycamper from Boston

Why jellied toast falls facedown.

Falling toast is often introduced into discussion with the idea that foolish people somehow believe that falling toast more often falls jelly downward because of bad luck or bad karma, whereas a more sophisticated person understands that, like flipping a coin, the toast has a 50-50 chance of falling face first and that foolish people only imagine that it usually falls jelly downward because jelly downward is the more memorable event. If the toast lands jelly first, you yell and stomp around and have a big memory, but if it lands jelly up, then you look around to see if you are alone and then pick it up and quietly carry on.

However, toast DOES fall jelly down more often! In fact, under typical conditions it falls jelly down every single time.

It is in the physics of the situation and easy to demonstrate. Objects have a certain rotational inertia such that for a given torque they get a certain rotational speed. Simultaneously, object take a certain amount of time to fall from a specific height. So now if you take an object, jellied toast, and a certain height, table height or waist height, you can completely model it's fall assuming that it starts its fall by being placed more than 50% off the edge of the table or hand (hence the fall). For typical toasts and tables, there is plenty of time in the fall for a first 180 degree rotation toward jelly side down, but not nearly enough time for a second 180 degree rotation back to safety.

It doesn't apply if you launch the toast into the air, or if you are dining on the edge of a skyscraper, but for most toast and most tables, it falls jellyside down.

Try it by placing a toast-sized paperback on the breakfast table, edge it sideways until it tips off and see the result.

The key lesson is to know that we hold incorrect beliefs about things all the time (in this case, a fun one, that falling toast is like flipping a coin), so we need to keep an open mind.

Dec. 05 2010 08:13 PM
Scott Murray from Fremont, CA

With all due respect to Dr. Tyson, a falling cat does not remain weightless as it falls. As it speeds up, the weight sensed by the cat of itself equals the drag force from air. Thus the weight experienced rises approximately with the square of falling speed, and acceleration decreases accordingly. As the cat approaches terminal velocity (where it is no longer accelerating) the cat experiences a sensation of normal weight. This is because drag approaches the cat's mass multiplied by the gravitational constant. The experience of a cat would therefore not be based on zero (or nearly zero) weight unless it has fallen a short distance. At long distances, it experiences (or approaches) a windy form or normal weight. [This response to weight sensation may play a roll in this factually complicated observation of a reported trend of more minor non-fatal injuries from higher falls, where dead cats and uninjured cats are not taken to a vet, and people might be more freaked out from cats that fell long distances, causing those with more minor injuries to be taken to the vet as well.] Perhaps a cat is disoriented by zero weight and is more easily oriented (and relaxed) as weight approaches normal during a long fall.

Dec. 05 2010 07:56 PM

quick info from Rochester Institute of Tech

doesn't list the paper, and the vid links are not working, but someone above posted the correct link

Dec. 04 2010 11:06 AM
Barbara from New Salem, MA

Could it just be that the cat needs time to position itself for a safer fall, and can't manage it in 5-9 stories? I don't know what a cat's terminal velocity is but I roughly calculate it would take 3 seconds to fall 4 stories and around 4 seconds to fall 8 stories (assuming ~10m each story). Not much time to get your cat act together after falling out window.

Dec. 03 2010 10:36 PM
Christopher C. Mills from Boulder, CO

Falling cats: What a mess (no humor intended)

Some tough love from a devoted listener: Radio Lab starts to loose me with shows like these.

Stochasticity was a mess, and now this.

The complete discombobulation of presented insight in this show makes you guys look like junior high school students with a tape recorder. Do your homework. The analysis of the falling cats was done correctly or it wasn't. This is an answerable question and answering it is within the realm of the resources of the show. Get an answer and present it. Don't leave it hanging. Don't leave it as though it is a matter of opinion-- it isn't. One of these guests was wrong about the cat data being skewed.

I am not sure where to start with my critique of this show at times. Are you just a couple of mystery junkies that don't actually care about understanding science any more than is necessary to catch a good mystery buzz that goes well with spacey inter-segment music? You might try magic mushrooms, a pair of headphones, and Pink Floyd instead of doing this show. (good humor intended)

It isn't bad that you find an error and then correct it with a future segment. Its bad that you compound the error in the followup segment, and then drop the entire issue with no meaningful resolution. You do this on a show whose whole point is ostensibly to leave its listeners with a sense of insight.

Here is a suggestion: Had you got somebody on staff with powerful influence over show content that actually understood the issues and subtleties of the subject matter that the Stochasticity show was attempting to present, and who had then worked to resolve them properly for the listener on that show, you might have gained the proper insight to properly clear up this current mistake with clarity. You may even have simply avoided making it in the first place.

Here is a possible insight for you: statistics, probability, randomness, extracting meaning from data, natural human misperceptions and superstitions, etc. are topics full of deep subtleties. You should either get your arms around these topics before you present them, or don't bother trying. There are plenty of mysteries to present. You shouldn't be turning things that aren't mysterious into mysteries simply because you don't get them yourselves.

This is a fun show-- I love the inter-segment astrotunes that go along with the presented insights. But a show like this without discipline might as well be about UFOs. The more it feels undisciplined, the less interested in the show I become.

Dec. 03 2010 08:45 PM

I also would love to hear a podcast covering some of the alternative theories on gravity!
Please look into the work of Tom Van Flandern for an alternate model of gravity. Very fun and interesting topic.

Dec. 03 2010 08:10 PM

I hate this show, I hate the production, the topics the silly humor, the false irony and most of all I hate the schedule. They cut off Fresh Air every week!!!! The only reason they're on is because it's locally produced by someone management must like. Snarky!!!

Dec. 03 2010 02:53 PM
MTS from Cincinnati

I still think that Kimberley Miner's cat-and-toast short animation says it all.

I just want the contract for laying the white carpet from Cincinnati to Cleveland if the train thing ever really happens in Ohio.

Dec. 03 2010 01:13 AM

There is a lot of confusion here, and people making a lot of assumptions and ill informed claims. As usual, the show has on two opposing views, both are merited and correct, yet could possibly have phrased what they say a bit better. For the sake of basic physics, in a vacuum or not, there are few things to get straight: Velocity/Speed and Acceleration are not the same thing, people are confusing "constant velocity" and "constant acceleration" as well as the different between "constant acceleration" and "changing acceleration" In order to accelerate (there is no such thing as "decelerate") it requires a change in vector, meaning either a change in speed/velocity, or direction. Traveling a constant speed and direction means you are not accelerating, (technically impossible to do, but save that for another time). We only feel CHANGES in acceleration, which is why we don't feel the constant "G" force of the both gravity and the spin of the earth moving us, they are constant and we are used to them, ;). When in free fall, you fall at 9.8 m/s/s CONSTANTLY, so you will not feel it, however you WILL feel the CHANGE in acceleration from not falling to falling, or wind blasting you sideways, or flipping over. All that taken away, there is no difference between free fall and standing still on earth regardless of speed. It is not speed that we feel (unless you meet resistance), and it is not actually acceleration we feel, it is the CHANGE in acceleration, which is why falling at a zillion miles an hour won't kill you, but hitting the ground and changing from a zillion to zero in nearly an instant will.

As for cats, yes, they do relax, to some extent, just as we do when falling. Once the initial shock of "falling" (CHANGE in ACCELERATION) (and not accounting for adrenaline, wind, etc) your body will relax somewhat. No one said they just go to sleep, but yes, it does relax. Some of it may be physiologically instinctual and simply automatic on the muscle's part, but it is enough for the "flying squirrel effect" to happen, as well as the the complex mechanics of the leg joints to prepare for impact which they are much better equipped for than our own.

Dec. 02 2010 09:17 PM

I've got to disagree with Dr. Tyson on not being able to feel the difference between free fall and terminal velocity. When you are on an airplane, you are traveling at constant velocity, and it feels just like being on earth. However, during turbulence, the plane can fall a few feet, and these moments most certainly feel different than the rest of the flight. I could imagine it is the same for a falling cat.

Dec. 02 2010 07:39 PM
Mark C from Highlands Ranch, CO

I disagree with the notion that this is not an "experimentally addressible question." Not too far from where I live is an indoor skydiving operation, where you can enter a vertical wind tunnel to experience the sensations of skydiving without the risk.

Certainly an experiment can be contrived making use of one of these facilities (I know of another in Orlando, FL), enabling scientific observations of cats, without exposing them to the danger of the sudden stop at the end of their fall.

Dec. 02 2010 07:10 PM
Edwin from Berkeley CA

While my cat is remaining mum on this subject, I would suggest that there is something to be said for the change in the experience of an incident over time, no matter how catastrophic. (no pun intended) I remember reading interviews of people who had experienced the 1964 Alaskan earthquake (aka the Good Friday Earthquake) that was nearly five minutes in duration with a magnitude of 9.2, and many of those people reported feeling something like ‘boredom’ after the first minute or so, along with ‘irritation’ in that it was taking so long, in the vein of ‘when is this stupid thing going to be over?’.
I would suggest that since cats are mammals too that their experience of falling changes over time and might account for the transition to ‘flying squirrel mode’ you describe. While this leaves out the whole terminal velocity thing, I find it much more plausible.

Also in listening to the story on vertigo I couldn’t help thinking how lucky this woman was to have onset be so subtle. My experience was sudden and horrific, so much so that it actually disturbed my speech. When my wife found me heaped on the sofa in a quivering frightened mass I looked at her and my mind formed the phrase ‘I think it’s time to go to the hospital’ but what I heard come from my mouth was ‘Doctor building’. This was the single most horrific moment of my life. I thought I must have had some sort of cerebral incident and that my life as I had known it was over.

Dec. 02 2010 04:05 PM
James Birk from NYC

I think I can shed some light on this cat business with the falling and the relaxing bit.

A million years ago, when I wore a lot of spats (I was a bit behind the times in 1989), I tried an experiment to see how each of my three cats would look wearing one. I wrapped the first cat's middle in the spat and buttoned it up the back, which created a very small amount of compression on the cat's mid-section.

I could slide a finger in, so I wasn't too worried about suffocation and the like, but when I put my cat on the floor, with the spat wrapped around its middle---

It couldn't stand. It was absolutely limp. I picked it up again and put it on all four feet, and it flopped over instantly. So I tried it with the second cat, same thing.

Third cat, same thing.

Here's my conjecture:

There may be a physiological response, at least in some types of domesticated felines, which causes a cat's large skeletal muscles to lose tension when pressure is applied to a large part of their mid-section, particularly their chest and bellies. That is precisely what the spat did.

And, I think it's something close to what the air rushing past a cat is doing when the cat is traveling through it at 80 mph or so. The chest and belly are compressed slightly (as anyone who's jumped out of a plane knows, or even stood strong against that damn wind on third avenue and 17th street), and to my mind, this results immediately in the physiological response of limpness.

We know that cat's have this sort of thing going on anyhow, pick even a small adult cat (so you won't hurt it) by the scruff of the neck, and its skeletal muscles contract in a very specific way, seemingly completely independent of any thought that cat might be having in the moment.

Dec. 02 2010 03:56 PM
ptbeale from Littleton MA

From the show Neil deGrasse Tyson said "the cat is as weightless the moment they leave the window as they are when they approach the terminal speed." Clearly Dr. Tyson hasn't jumped out of a plane!

What you'll feel , for maybe a second, first hand, when you jump out of a plane is the sensation of 0G {I call that free fall} i.e. not the normal 1G of gravity. As you approach terminal velocity and the wind pushes you harder and harder, you again experience 1G.

At terminal velocity, you are again feeling like {from a sensation of gravity point of view} like you are standing on the ground, despite the fact that you are plummeting to the ground with only a parachute to save you.

Maybe 0G isn't good for a cats state of mind?

Dec. 02 2010 03:07 PM
James R.

I would really like to see your podcast cover some of the new notions about Gravity put forward by people like Erik Verlinde at the the University of Amsterdam, who see gravity as an emergent property of the universe caused by entropy, and not a force in and of itself.

Dec. 02 2010 12:40 AM

Leave a Comment

Email addresses are required but never displayed.

Supported by