Problem with cats surviving high falls

[himanshu2004@]

Problem with cats surviving high falls! :)

I've been reengaging with physics since I'd stopped formally studying it after high school (with the exception of a little bit I we had during studying computer science at university).

So I was revising my concepts of inertial frames, non intertial frames, "fictitious" forces experienced during acceleration etc, and I remembered reading in a book by Hallilday and Resnick that cats survive falls from higher places better than from lower ones (with 4-5 floors being the most dangerous height). I couldn't exactly reason out why it would happen and so I searched it on the web again and this seems to be the reason:

Cats relax after reaching terminal velocity. This causes them to spread out their posture, which reduces their terminal velocity. The further explanation given is that we can feel acceleration (and not uniform velocity).

I have a problem with this explanation, because we should only be able to "feel" acceleration when we are being accelerated by the push or pull, so to speak, of the accelerating frame. This should not happen in when accelerating due to the effect of gravity, because all of our atoms would be experiencing the same acceleration.

So, is there a problem with the explanation, and if so, what is the right explanation?


Thanks!

 

[superg33k]

The cat feels the push up of ground against gravity when it is standing on the ground. When it is free-falling, there is no push up from the ground, it feels this difference and relaxes.

 

[himanshu2004@]

Ah, you miss the question.
Why does it only relax after reaching terminal velocity?

 

[superg33k]

I'm only guessing here:

Cats priorities: 1 - land on feet, 2 - slow down
Cats dilema: Spreading its legs to slow itself down reduces the chance of landing on its feet

Once the cat reaches terminal velocity, it realizes that it will significantly slow itself down by spreading its legs, but before that point it's much more concerned with having its feet pointed downwards. (probably all instinct rather than conscious thoughts)

Then we still have the question how does the cat 'feel' it reaches terminal velocity when it can only 'feel' the force due to acceleration, which it has had ever since it was dropped. Either it feels the increased air resistance, or it reacts after falling for a certain time, or it sees the ground coming rapidly towards it.

I've never had a cat.

 

[russ_watters]

I have a problem with this explanation, because we should only be able to "feel" acceleration when we are being accelerated by the push or pull, so to speak, of the accelerating frame. This should not happen in when accelerating due to the effect of gravity, because all of our atoms would be experiencing the same acceleration.

So, is there a problem with the explanation, and if so, what is the right explanation?

If you can feel an acceleration, you can feel the difference between an acceleration and a [sudden] lack of acceleration. For falling (when vertical anyway), it's the feeling of your stomach lifting inside your abdomen.

 

[Borek]

I've never had a cat.

Nobody ever had a cat. Some people are/were owned by cats. Sometimes cats allow people to live with them, but that's all.

Now I should ban myself for OT posting.

 

[himanshu2004@]

If you can feel an acceleration, you can feel the difference between an acceleration and a [sudden] lack of acceleration. For falling (when vertical anyway), it's the feeling of your stomach lifting inside your abdomon.

1) Why should the stomach lift inside the abdomen; the stomach would be accelerated downward just as the abdomen would be. No? Wouldn't it be more accurate to say I would feel a change from experiencing weight to experiencing weightlessness. Anyway, this change would be nearly instantaneous (unlike reaching terminal velocity which would take much longer).

2) My question wasn't about the difference between the cat being at rest and suddenly entering free fall, but about what difference its reaching terminal velocity makes. As is suggested at http://ffden-2.phys.uaf.edu/211.web.stuff/Kuhns/Index.htm
and in presumably in some the works referenced (I certainly remember reading something similar in Halliday-Resnick)

 

[JaredJames]

1) Why should the stomach lift inside the abdomen; the stomach would be accelerated downward just as the abdomen would be. No? Wouldn't it be more accurate to say I would feel a change from experiencing weight to experiencing weightlessness. And this change would be nearly instantaneous (unlike reaching terminal velocity which would take much longer).

Why would everything fall at the same rate?

Your body starts accelerating downwards, but that has to be transmitted to the internal organs via a medium. Everything isn't inelastically attached to everything else.

Only in a vacuum will everything fall at the same rate.

 

[himanshu2004@]

Why would everything fall at the same rate?

Your body starts accelerating downwards, but that has to be transmitted to the internal organs via a medium. Everything isn't inelastically attached to everything else.

Only in a vacuum will everything fall at the same rate.

My question was point 2) and this is somewhat of a digression. But to reply to your post, the downward acceleration does NOT have to have transmitted to the internal organs via a medium; they are influenced by the force of gravity just as the outer body is.

 

[JaredJames]

My question was point 2) and this is somewhat of a digression. But to reply to your post, the downward acceleration does NOT have to have transmitted to the internal organs via a medium; they are influenced by the force of gravity just as the outer body is.

The force of gravity obviously doesn't, but the motion of the body does. All of your organs don't just suddenly go "we're falling" and do it immediately in time with your big toe.

 

[Drakkith]

The force of gravity obviously doesn't, but the motion of the body does. All of your organs don't just suddenly go "we're falling" and do it immediately in time with your big toe.

Umm, I'm pretty sure that's exactly how it works when you start falling. Your whole body and everything in it is accelerated at the same speed at the same time.

 

[JaredJames]

Umm, I'm pretty sure that's exactly how it works when you start falling. Your whole body and everything in it is accelerated at the same speed at the same time.

A crude analogy, imagine an air filled balloon sitting on the floor of a metal box, attached to the side by a length elastic. You suddenly drop the box. The balloon does not fall at the same rate as the box and is likely to hit the roof of the box. It is "left behind" for a short while. It's the same effect in your body.

Your whole body and everything in it may be subject to the same force from gravity, but it doesn't mean it will fall at the same rate whilst in a medium.

 

[himanshu2004@]

The force of gravity obviously doesn't, but the motion of the body does. All of your organs don't just suddenly go "we're falling" and do it immediately in time with your big toe.

I agree with that, and then it got nothing to do with "internal" organs versus "external" ones as you'd put it, but rather the "higher" parts of the body versus the "lower" parts they were resting on.
But like I said, whatever the changes due to these effects, these are almost instantaneous, and occur long before the point of reaching terminal velocity. So, why is the cat supposed to relax after reaching terminal velocity?

 

[JaredJames]

I agree with that, and then it got nothing to do with "internal" organs versus "external" ones as you'd put it, but rather the "higher" parts of the body versus the "lower" parts they were resting on.
But like I said, whatever the changes due to these effects, these are almost instantaneous, and occur long before the point of reaching terminal velocity. So, why is the cat supposed to relax after reaching terminal velocity?

Whilst accelerating in a fast car, you are constantly pinned to your seat. It is only once you reach a steady speed that you can move around normally under equilibrium conditions.

If you can feel the acceleration and then the switch to constant speed (equilibrium) it shouldn't be hard to judge.

 

[Drakkith]

A crude analogy, imagine an air filled balloon sitting on the floor of a metal box, attached to the side by a length elastic. You suddenly drop the box. The balloon does not fall at the same rate as the box and is likely to hit the roof of the box. It is "left behind" for a short while. It's the same effect in your body.

Your whole body and everything in it may be subject to the same force from gravity, but it doesn't mean it will fall at the same rate whilst in a medium.

Actually I'm pretty sure the balloon would fall at the same rate as everything else. Remember that the balloon is NOT falling through the medium, the box is. The balloon is inside the box and has no contact with anything outside, similar to your body.

 

[Drakkith]

Whilst accelerating in a fast car, you are constantly pinned to your seat. It is only once you reach a steady speed that you can move around normally under equilibrium conditions.

If you can feel the acceleration and then the switch to constant speed (equilibrium) it shouldn't be hard to judge.

Agreed. Once you reach terminal velocity you no longer feel like your falling because the resistance of the air is in equilibrium with gravity. I believe you would feel like your lying on the ground or something similar.

 

[JaredJames]

Actually I'm pretty sure the balloon would fall at the same rate as everything else. Remember that the balloon is NOT falling through the medium, the box is. The balloon is inside the box and has no contact with anything outside, similar to your body.

Train decelerating, you fall forwards.

Car accelerating, you are pinned to seat.

To take it further, when you accelerate / decelerate, the air pressure changes internally to a slight gradient - shown where a helium balloon will move opposite to acceleration.

 

[himanshu2004@]

A crude analogy, imagine an air filled balloon sitting on the floor of a metal box, attached to the side by a length elastic. You suddenly drop the box. The balloon does not fall at the same rate as the box and is likely to hit the roof of the box. It is "left behind" for a short while. It's the same effect in your body.

Your whole body and everything in it may be subject to the same force from gravity, but it doesn't mean it will fall at the same rate whilst in a medium.

That seems completely incorrect. (Ignore my previous post, it was in a different context.)

I am pretty sure that if the metal box is air-tight, the balloon would fall exactly as the same rate as the box. In any case, how is the material inside the balloon relevant?

 

[Drakkith]

Train decelerating, you fall forwards.

Car accelerating, you are pinned to seat.

None of that is like gravity. Gravity pulls everything in your body down at the same time, an accelerating train or car does not.

 

[JaredJames]

In any case, how is the material inside the balloon relevant?

Huh?

 

[himanshu2004@]

Whilst accelerating in a fast car, you are constantly pinned to your seat. It is only once you reach a steady speed that you can move around normally under equilibrium conditions.

If you can feel the acceleration and then the switch to constant speed (equilibrium) it shouldn't be hard to judge.

Incorrect again. In an accelerating car, you can feel the acceleration, because you are "pushed" by accelerating car (like I said in the starting post of the thread), and the part of you which gets pushed first pushes the other parts and so on.

Accelerating due to free fall, you cannot feel that acceleration, because nothing in your body is pushing or pulling anything.

 

[JaredJames]

None of that is like gravity. Gravity pulls everything in your body down at the same time, an accelerating train or car does not.

So now I'm curious what causes the "stomach left behind" feeling?

 

[JaredJames]

Accelerating due to free fall, you cannot feel that acceleration, because nothing in your body is pushing or pulling anything.

Air resistance? You'll get some sensation at least.

 

[Drakkith]

So now I'm curious what causes the "stomach left behind" feeling?

It most definitely is not your stomach being "left behind". I've gotten that feeling just sitting in front of an IMAX screen or right before I go over the top of a roller coaster. It is something more like excitement or fear or something.

 

[Drakkith]

Air resistance? You'll get some sensation at least.

Yes, you would be able to tell you are moving due to the air resistance, and probably tell that you are accelerating.

Now imagine if you were on one of those 747's or whatever they use to train astronauts for zero G. The plane goes into a controlled dive and you begin to free fall. Can you tell you are accelerating? Nope.

 

[himanshu2004@]

Agreed. Once you reach terminal velocity you no longer feel like your falling because the resistance of the air is in equilibrium with gravity. I believe you would feel like your lying on the ground or something similar.

I believe that might make sense. Because its only after reaching terminal velocity that the cat experiences as much "upward push" as it is used to experiencing while standing/sitting on the ground.

 

[himanshu2004@]

Air resistance? You'll get some sensation at least.

Air resistance certainly, but that's got only to do with velocity against the air. You would feel air resistance even if you were moving against air at a constant velocity.

So now I'm curious what causes the "stomach left behind" feeling?

To the extent that its a real feeling, it happens because your stomach is used the effect of feeling its weight, which makes it push downward against the abdomen. In weightlessness, the stomach is felt to be slightly closer to your chest than you're used to.
In fact, if you hung upside down, you would feel that doubly strongly.
But yes, its nothing more than that.
In any case when free falling, your stomach should feel the same that of astronauts floating peacefully in zero gravity space :)

 

[himanshu2004@]

It most definitely is not your stomach being "left behind". I've gotten that feeling just sitting in front of an IMAX screen or right before I go over the top of a roller coaster. It is something more like excitement or fear or something.

Its at least partly physical as mentioned above since it feels different from the usual state. In a roller coaster your stomach anyways does get left behind when its accelerating/decelerating, due to inertia.

 

[superg33k]

Half of these posts use the word falling as an acceleration. The other half use it as a velocity.

 

[BruceW]

The stomach "left behind" feeling is due to your body getting accelerated by a contact force - so then your body exerts a contact force on your stomach (so that it accelerates along with the body), which makes the feeling.
In gravity, with no air resistance, there is no "left behind" feeling, since gravity acts on the whole body including the stomach. In fact, there is no feeling at all. You wouldn't be able to tell the difference from just being motionless in space. (Apart from the fact that you'd be getting closer to the planet).
For the falling cat, it would feel the air resistance increasing as it sped up, then at terminal velocity, the air resistance would become constant.

 

[himanshu2004@]

@superg33k
I did a quick ctrl-F and didn't spot any ambiguity. "Falling" has always been used to mean free-falling, which is obvious given the context of this thread.

In any case, all questions seem to have been resolved a while back, so why so serious? :)

 

[himanshu2004@]

In fact, there is no feeling at all. You wouldn't be able to tell the difference from just being motionless in space. (Apart from the fact that you'd be getting closer to the planet).

The point is, we are not used to being in space, so there would be a feeling in free-fall that feels different from standing on the ground. (edit: and you'd stop feeling that difference after whatever hours/days of being in space since you'd get used to that feeling, and then being back on the Earth might feel different for a while.)

For the falling cat, it would feel the air resistance increasing as it sped up, then at terminal velocity, the air resistance would become constant.

As pointed above, I think its got more to do with the upward push due to the air resistance at terminal velocity being the same as the upward push we are used to feeling when on the ground, which is what makes the cat relax.
And as I just thought, even after the cat's terminal velocity decreases as it slows down after relaxing and spreading out, the upward force would still continue to be the same.

 

[Lsos]

As russ watters mentioned, you can definitely feel the difference between falling due to gravity and being at terminal velocity. Terminal velocity you feel just like on earth, except there's a lot of wind. Falling, or weightlessness, you feel...well, weightless. There are amusement park rides that rely on this feeling, and astronauts have to train for it. I can definitely see a cat getting freaked out and/or reacting to this. In fact, it's probably the stimulus that on their turning mechanism is tuned to.

Edit: When I started writing this, it was supposed to be right after russ watter's post on the first page. By the time I managed to post it...I see it's been already beaten to death.

 

[himanshu2004@]

Yeah, I agree. You explained it much better than Russ did (and his mentioning the word "sudden" when talking about the change in acceleration versus the lack of it didn't really help because in fact after the initial point of falling the cat experiences a gradual change in the acceleration/force it feels, till it becomes equal to what the cat feels on the ground, at which point it relaxes).
Though the thread did reach the same conclusion a while back eventually, thanks for confirming.

 

[russ_watters]

1) Why should the stomach lift inside the abdomen; the stomach would be accelerated downward just as the abdomen would be.

Again, you are thinking about it backwards: the force of gravity isn't lifting your stomach, it is just no longer pulling it down wrt the rest of your body. You notice what you lose: your legs pushing you up and the hydrostatic pressure of the weight of your guts sitting on your pelvis.

2) My question wasn't about the difference between the cat being at rest and suddenly entering free fall, but about what difference its reaching terminal velocity makes. As is suggested at http://ffden-2.phys.uaf.edu/211.web.stuff/Kuhns/Index.htm
and in presumably in some the works referenced (I certainly remember reading something similar in Halliday-Resnick)

Ok, well again, think about what changed. When a cat is standing on the ground its guts and head are hanging off its spine. In freefall, they aren't. When at terminal velocity, it is more like floating in water or lying in a soft bed: the force of gravity still tries to crush you, but is opposed by the somewhat uniform drag force instead of the structure of your bones.