High School Falling Cat - Rotation with Zero Total Angular Momentum

[A.T.]

I made a new version of the falling cat video, with narration. It explains how cats turn around while having zero net angular momentum during the fall:

 

[anorlunda]

Wow. That's very clever. I'll have to re-watch it several times to grok the zero total.

 

[A.T.]

Wow. That's very clever. I'll have to re-watch it several times to grok the zero total.

It is easier to grok, when you imagine the cat bends 180° into a U-shape. Then its obvious that the ends of the U have opposite angular momenta. But real cats do not bend than much, so you need vectors.

 

[hutchphd]

My cat can't do vectors. I better not show her.
Nice animation!

 

[RPinPA]

For a similar analysis with squirrels, check out this hilarious video by Mark Rober, an engineer with way too much time on his hands. Link should take you to 15:59 where the discussion begins.

 

[Spinnor]

At the 1:07 point of the following video is an upside down cat which is dropped, best watched I think at 1/4 speed.



I think the physics is more complicated then explained in post 1?

See the 0:00 mark and the 1:54 mark for more analysis of the problem in the following video,



I don't who is right I am just suspicious of the answer given by A.T., the first video of the falling cat does not seem to jive with A.T.'s explanation. Maybe a combination of both explanations?

Thanks.

 

[A.T.]

I don't who is right I am just suspicious of the answer given by A.T., the first video of the falling cat does not seem to jive with A.T.'s explanation. Maybe a combination of both explanations?

My video explains the core mechanism of how it is possible physically. Nature, especially biology is always more complex. The motion of a real cat's halves is often less symmetrical, which is likely dictated by physiology and preferred landing pose to dampen the impact better.

 

[Spinnor]

My video explains the core mechanism of how it is possible physically. Nature, especially biology is always more complex. The motion of a real cat's halves is often less symmetrical, which is likely dictated by physiology and preferred landing pose to dampen the impact better.

I got distracted looking for differences in the video I posted and forgot to like your video which immediately makes clear the general physics of the cats motion. Looking at old posts of mine gave me another chance to like a great video. Thanks.

 

[A.T.]

I got distracted looking for differences in the video I posted and forgot to like your video which immediately makes clear the general physics of the cats motion. Looking at old posts of mine gave me another chance to like a great video. Thanks.

You're welcome. Both Destin and Mark Rober in the videos linked above correctly point out that real animals sometimes turn around the front of the body first, then the back, by varying the moments of inertia. Likely because they prefer to see where they are going and/or want to land on a certain pair of legs first. But in other videos, especially when a cat falls from a small height and has to turn very quickly, it is more symmetrical like in my video.

 

[256bits]

You're welcome. Both Derek and Mark Rober in the videos linked above correctly point out that real animals sometimes turn around the front of the body first, then the back, by varying the moments of inertia. Likely because they prefer to see where they are going and/or want to land on a certain pair of legs first. But in other videos, especially when a cat falls from a small height and has to turn very quickly, it is more symmetrical like in my video.

when are you going to do a simulation summersalt ( somersault - phonetics is great ) with twist off the diving board.


Here some math people envision a 1.5 rotation with 5 twists as being possible.
https://www.technologyreview.com/20...ly-new-dive-with-5-twists-and-15-somersaults/

A PDF from the arxiv
https://arxiv.org/abs/1612.06455

 

[Spinnor]

when are you going to do a simulation summersalt ( somersault - phonetics is great ) with twist off the diving board.


Here some math people envision a 1.5 rotation with 5 twists as being possible.
https://www.technologyreview.com/20...ly-new-dive-with-5-twists-and-15-somersaults/

A PDF from the arxiv
https://arxiv.org/abs/1612.06455

Since height is a limiting factor to more twists I wonder if any trainging facility might add height to the diving platform and then vary the height

when are you going to do a simulation summersalt ( somersault - phonetics is great ) with twist off the diving board.


Here some math people envision a 1.5 rotation with 5 twists as being possible.
https://www.technologyreview.com/20...ly-new-dive-with-5-twists-and-15-somersaults/

A PDF from the arxiv
https://arxiv.org/abs/1612.06455

One limiting factor in the above analysis of the number of possible twists is platform height. It would be "easy" to make a diving platform with an adjustable height. Nail the 5 twists at a height greater than 10 meters and then as technique improves lower the platform towards 10 meters? A quick Google search does not come up with such an adjustable training platform.

 

[Orodruin]

One limiting factor in the above analysis of the number of possible twists is platform height.

Well, height here is just a proxy for time. One easy way to increase time is to be in free fall, for example in orbit at the ISS or parabolic flight.

 

[A.T.]

Well, height here is just a proxy for time. One easy way to increase time is to be in free fall, for example in orbit at the ISS or parabolic flight.

In the below parabolic flight video at 0:11 a cat makes ~8 rotations in 5sec.



In most zero-g videos I saw cats just float around and relax. But here the evil NASA guy was throwing it against the wall.

 

[Spinnor]

From Google search "gymnastics slow motion twisting angular momentum"

https://www.youtube.com/results?search_query=gymnastics+slow+motion+twisting+angular+momentum

Has anyone ever suspended a gymnast upside-down, like a cat by its paws, and let them go to see if they could land on their "paws"? The guy in the video looks like he could have done so? This could be done over a pool or a foam pit so the gymnast was not hurt.

Thanks.

Edit, start the video at 2:21 to see the gymnast do a "cat twist".