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Thread: conceptual question

  1. #1 conceptual question 
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    why does a cat dropped from say 10 th floor of a skyscraper land on its paws???
    Though if a person is dropped he dies in a moment.?????
    give the mission


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  3. #2  
    WYSIWYG Moderator marnixR's Avatar
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    lower weight means lower terminal velocity + given enough time a cat adopts a sort of "parachute" position

    this means that paradoxically more cats die from their injuries when falling from a lower than a higher height (from a lower the terminal velocity is the same but the cat hasn't been able to twist itself in the correct position


    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  4. #3  
    Forum Freshman BenTheMan's Avatar
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    Sounds like something we should test...
    Sometimes you eat the bahr, and, well, sometimes he eats you. ---Anon
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  5. #4  
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    Quote Originally Posted by marnixR
    lower weight means lower terminal velocity + given enough time a cat adopts a sort of "parachute" position
    Not quite correct. Terminal velocity is the same for all objects with the exception of those that are extremely lightweight - like a feather, sheet of paper and similar things. Momentum is what is different. The more mass (weight) the greater the momentum becomes.

    The "parachute position" thing isn't accurate either. A cat is unable to stretch it's skin in the same fashion that a flying squirrel does. It's not attached in the same fashion.
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  6. #5  
    Forum Freshman StarMountainKid's Avatar
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    It's because cats have 9 lives.
    "Where are you going?" "I go where it is changeless." "How can you go where it is changeless?" "My going is no change."
    http://www.youtube.com/user/starmoun...d?feature=mhee
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    WYSIWYG Moderator marnixR's Avatar
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    Quote Originally Posted by Old Geezer
    Quote Originally Posted by marnixR
    lower weight means lower terminal velocity + given enough time a cat adopts a sort of "parachute" position
    Not quite correct. Terminal velocity is the same for all objects with the exception of those that are extremely lightweight - like a feather, sheet of paper and similar things. Momentum is what is different. The more mass (weight) the greater the momentum becomes.

    The "parachute position" thing isn't accurate either. A cat is unable to stretch it's skin in the same fashion that a flying squirrel does. It's not attached in the same fashion.
    surely terminal velocity must take air resistance into acount ? i know about the famous galileo thought experiment, but a feather and a lead ball will only reach the ground at the same time if there is no air resistance

    + when i say the parachute position, i didn't mean in the sense of a flying squirrel, but cats do assume a position that exposes the greatest possible surface area to air resistance
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  8. #7  
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    [quote="marnixR"]
    Quote Originally Posted by Old Geezer
    Quote Originally Posted by marnixR
    lower weight means lower terminal velocity + given enough time a cat adopts a sort of "parachute" position
    Not quite correct. Terminal velocity is the same for all objects with the exception of those that are extremely lightweight - like a feather, sheet of paper and similar things. Momentum is what is different. The more mass (weight) the greater the momentum becomes.

    The "parachute position" thing isn't accurate either. A cat is unable to stretch it's skin in the same fashion that a flying squirrel does. It's not attached in the same fashion.
    surely terminal velocity must take air resistance into acount ? i know about the famous galileo thought experiment, but a feather and a lead ball will only reach the ground at the same time if there is no air resistance
    Yes, air resistance is a factor but is practically the same for most objects as I mentioned earlier. For what it's worth, Galileo's experiment wasn't thought but actually physical. As the story goes, he performed the experiment at the Tower of Pisa.

    + when i say the parachute position, i didn't mean in the sense of a flying squirrel, but cats do assume a position that exposes the greatest possible surface area to air resistance
    Still not accurate, I'm afraid. View a cat's body in profile. It's the same from top or bottom and presents less surface area than when viewed from the side. :wink:
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  9. #8  
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    First let's clear up some misconceptions. A cat dropped from a serious height onto a hard surface has practically no chance of survival, even though it will generally land on its feet. We occasionally hear of a few amazing survival feats after falls from great heights, either for a cat or a human, but these are exceptional. There is always some sort of cushioning at the finish.

    Next, terminal velocity can be quite variable even for a particular object. It will depend on streamlining and tumbling, for example. Ask any skydiver who knows about joining his buddies in the free fall formation. By altering his configuration to the airstream he is able to vary his velocity from about 110 mph to about 185 mph.

    But is this what the original poster is asking? Or does he really want to know why a cat always lands on its feet?

    There actually have been studies on just this question. The scientists tossed cats off the top of a ladder (onto a presumably well-padded surface). The high-speed camera showed how the cats managed their aerial acrobatics -- in mid-air, a cat spins its tail! *This is how the cat is able to twist its body to the paws-first position. *It's an example of the well-known principle of conservation of angular momentum.
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  10. #9 conceptual question 
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    mr.steve f ,talking about clearing the misconceptions ,when the answer to it is quite simple????this is myself "AVINASH MEHTA" who had posted the question.the explanation is:-
    STATUTORY WARNING:-(THIS EXPLANATION REQUIRES PATIENCE TO UNDERSTAND.ANYBODY NOT HAVING PATIENCE MAY NOT READ IT.)

    When a cat is dropped from a height(considerably say 10m),be it in any position at some instant of time it becomes horizontal.At this point its centre of mass and centre of gravity coincide (virtual position being the stomach).Now the cat stretches its front legs away from itself ,both the legs being parallel.Similarly it does this with the back legs too.Thus its centre of mass though remains stationery(as no external force is acting) but its centre of gravity shifts towards its face(virtually).Now weight "mg" acting on it at the centre of gravity tend it to have a rotational motion and thus finally the cat spins 180 degrees.This happens in a fraction of second.Also, the cat being lighter(than human being) takes more time to come down.Thus as the cat rotates 180 degrees from upside down to normal position it lands on its soft paws safely."HAPPY ENDING"
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    avinash mehta
    its centre of mass though remains stationery(as no external force is acting) but its centre of gravity shifts towards its face(virtually).Now weight "mg" acting on it at the centre of gravity tend it to have a rotational motion and thus finally the cat spins 180 degrees.
    How can the center of gravity be different than the center of mass? How did the center of gravity shift toward its face by the cat stretching out its legs? How would the weight acting on the center of gravity (near the cat's face or anywhere else) cause a rotational motion?
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  12. #11  
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    I am glad you came back, Avinash Mehta, so I can ask you a question.

    Why did you post your original question? You apparently knew the answer, so what information were you seeking?
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  13. #12 conceptual question 
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    Mr SteveF:- this site being there for conceptual debates ,iposted my question to test myself whether anybody knew a better ans. to it
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  14. #13 Re: conceptual question 
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    Quote Originally Posted by avinash mehta
    mr.steve f ,talking about clearing the misconceptions ,when the answer to it is quite simple????this is myself "AVINASH MEHTA" who had posted the question.the explanation is:-
    STATUTORY WARNING:-(THIS EXPLANATION REQUIRES PATIENCE TO UNDERSTAND.ANYBODY NOT HAVING PATIENCE MAY NOT READ IT.)

    When a cat is dropped from a height(considerably say 10m),be it in any position at some instant of time it becomes horizontal.At this point its centre of mass and centre of gravity coincide (virtual position being the stomach).Now the cat stretches its front legs away from itself ,both the legs being parallel.Similarly it does this with the back legs too.Thus its centre of mass though remains stationery(as no external force is acting) but its centre of gravity shifts towards its face(virtually).Now weight "mg" acting on it at the centre of gravity tend it to have a rotational motion and thus finally the cat spins 180 degrees.This happens in a fraction of second.Also, the cat being lighter(than human being) takes more time to come down.Thus as the cat rotates 180 degrees from upside down to normal position it lands on its soft paws safely."HAPPY ENDING"
    It required little patience nor was it useful. The "information" it provided is incorrect.

    There is no shifting of the center of gravity, it remains where it always was. And indeed, there IS an external force in action - that of gravity.

    And the statement about the cat being lighter than a human is meaningless also. The terminal velocity for each is exactly the same. Look up the term "terminal velocity" and do a bit of studying. :wink:
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  15. #14  
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    Thank you Avinash Mehta for that reply.

    Be aware that in a uniform gravitational field, the center of gravity and the center of mass are always the same point. Also, a body in free fall does not automatically rotate so its center of gravity is at its lower point.

    Are you still satisfied you have the best answer? How did you rate my explanation of the cat consciously twisting into the paws-down position?
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    MR stevef .good to meet u on this site .i am satisfied with ur reply.
    Mr old greezer please don't be over confident 'bout ur concepts.take my reply in the right spirit.
    i have said previously ths question was posted to find if anyone has a better reply.
    Now as the term "terminal velocity" has creeped in plz could anyone explain it to me in detail??
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  17. #16  
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    Quote Originally Posted by avinash mehta
    MR stevef .good to meet u on this site .i am satisfied with ur reply.
    Mr old greezer please don't be over confident 'bout ur concepts.take my reply in the right spirit.
    i have said previously ths question was posted to find if anyone has a better reply.
    Now as the term "terminal velocity" has creeped in plz could anyone explain it to me in detail??
    Terminal velocity is a very real and important factor to consider when talking about any free-falling body in the Earth's atmosphere. (Or any gravity well with an atmosphere, for that matter.)

    Rather than me writing a whole page explaining it, most of what you need to know can be found here: http://en.wikipedia.org/wiki/Terminal_velocity
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  18. #17  
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    At this point, I am not quite sure if adding another post will help. The amount of misinformation seems to be increasing (I think SteveF gave a decent answer somewhere in the middle). But let's try to help, anyway,...

    When a cat is dropped from a height(considerably say 10m),be it in any position at some instant of time it becomes horizontal.
    I cannot let this stand. If I let a dead stuffed cat drop with its head down (no initial rotation), there is no guarantee it will ever be horizontal before impact. It will likely fall on its head. A living cat, on the other hand, achieves a decent landing position by its own action, not by chance.

    At this point its centre of mass and centre of gravity coincide (virtual position being the stomach).
    Some guys have rightly expressed concern with the relevance of this statement. On the length scale of a cat, Earth's gravity has to be considered uniform. Hence, differences between centers of mass and gravity are negligible in this discussion.

    Now the cat stretches its front legs away from itself ,both the legs being parallel.Similarly it does this with the back legs too.Thus its centre of mass though remains stationery(as no external force is acting) but its centre of gravity shifts towards its face(virtually).Now weight "mg" acting on it at the centre of gravity tend it to have a rotational motion and thus finally the cat spins 180 degrees.This happens in a fraction of second.
    This is not entirely wrong, but it doesn't quite work like this. Shifting of the COG (as such) is not sufficient to change the rate of rotation (I'll explain in a second how stretching a leg works indirectly). In between the above lines I can clearly read the common misconception that heavier objects fall faster than light objects. A review of Newton's axioms will help to remove this misconception.

    By stretching the legs a cat can indeed change its rate of rotation, because the *moment of inertia* will change. Without external influence, angular momentum is constant, so a change of the moment of inertia will change the rotational velocity. Everyone has seen an ice dancer accelerate (or decelerate) a spin around the vertical axis by moving the arms in (or stretching them out). A cat can use this to her advantage, to get into the right position (and stay there). Furthermore, and this goes with SteveF's earlier comment, by rotation of the long tail, the cat can redistribute the angular momentum, controlling the body's rotation (the total angular momentum is still the same). And last but not least, stretching out or pulling in a leg will help the cat take advantage of external aerodynamic forces, and gain (or loose) rotational momentum. This is crucial if the initial rate of rotation is insufficient for a quick spin.

    Also, the cat being lighter(than human being) takes more time to come down.
    Alright, here we go. Please, familiarize yourself with the basic laws of motion. The minor difference between accelerations of cat and human is due only to aerodynamics, mainly because their shapes are different. It has nothing to do with weight.

    Thus as the cat rotates 180 degrees from upside down to normal position it lands on its soft paws safely."HAPPY ENDING"
    Well, you got this one right... hopefully. :wink:
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  19. #18  
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    A falling body will continue to accelerate unless acted upon by an external force. In the case of a body falling through the Earth's atmosphere that external force is air resistance. In practice a velocity is reached at which the resistance to increased velocity counters the acceleration due to gravity. The object will now fall at a constant speed. That is its terminal velocity.
    Old geezer seems reluctant to accept that terminal velocities are quite varied, depending upon the character of the object - and they don;t have to be as varied as feathers and lead balls. Steve F has made this quite clear with his skydiver illustration.
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  20. #19  
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    Terminal velocity is the point at which the drag of the atmosphere on the cat's body is equal to the gravitational pull, and the cat will thereafter fall at a constant speed. It depends on the weight of the cat (mass) and the viscosity of the atmosphere. Also, if the terminal velocity of the cat is great enough, the life of the cat on landing will be terminated.
    "Where are you going?" "I go where it is changeless." "How can you go where it is changeless?" "My going is no change."
    http://www.youtube.com/user/starmoun...d?feature=mhee
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    sorry if my answer seems to be very cheap and incompatible for the so scienctific discussion. But can it not be some locomotory system considering its body and shape.
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    A cat's landing is not always happy, even if it lands on its feet, but it has a lot better chance than a man falling from a great height.

    If we assume that a man has about the same shape as a cat, aerodynamically, but scaled up in size, it will have a higher terminal velocity. This is because the weight increases as the cube of the linear size, but the cross-sectional area only increases as the square. Thus the man will have a higher sectional density making him more aerodynamic.

    The other thing working against the man is the fact that the weight of an animal is proportional to the cube of the linear size, but the strength only increases as the square. This is why an ant can lift many times his weight, but we can't. Hence, the lighter cat probably has proportionally stronger bones in comparison to its weight.
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  23. #22  
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    Hii Mr avinash mehta,

    You haven't answered about the shift of center og gravity. As said before, in uniform gravity field, the center of gravity and the center of mass are always coincident.

    I still prefer about the conservation of angular momentum.
    Hope that you reply as soon as possible. Thanks.
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  24. #23  
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    I would say that this has as much to do with the architecture of a cats bone/muscle structure, and general skeletal shape in comparison to a humans as it does with anything else.

    They are able to withstand more impact energy with respect to their mass than a human skeletal structure can.

    My thoughts.
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