Why does the cat always touch the ground when it falls from a height?

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Why does the cat always touch the ground when it falls from a height?Cats need certain conditions to fall from a height to land on all fours.The minimum height is 5 cm. You can’t land on all fours below this height. However, scientific research has found that a cat can safely land on all fours when it is at least 30cm in height. When the height is too high, the cat is less likely to land on all fours and will get injured. In a 1987 study, it was found that when a cat fell from the height of a seven-story building, it would not touch the ground on all fours. Instead, it would choose to relax its body to increase air resistance and adopt a posture of a full-body landing.

This is called cat righting reflex, righting reflex, righting reflex, turning reflex, righting reflex and reset reflex. This article chooses to use the second one. If you see several others elsewhere, we are actually talking about the same thing.

A case study of cats falling from heights published in 2004 gives some data that allows us to see what happens when cats fall. Scientists have counted 119 cats falling from high floors in the four years from 1998 to 2001. 59.6% of these cats are less than one year old, and the average drop height is four stories high. Most of them fell during the hot season. . 96.5% of cats survived. But they are basically injured. 46.2% of cats had limb fractures, forearm fractures accounted for 38.5%, and hind limb fractures accounted for 61.5%. Tibia fractures were the most common (36.4%), followed by femur (23.6%). 78.6% of cats have fractures of the distal femur. The average age of patients with femoral fractures is 9.1 months, and the average age of patients with tibial fractures is 29.2 months. 33.6% of cats were diagnosed with chest trauma. The number of cats diagnosed with pneumothorax was 20%, and the proportion of lung contusions was 13.4%. Studies have found that falling from a height of seven floors and above will cause more serious injuries and a higher incidence of chest trauma.

Due to the high demand for animal protection, the study of cats falling from heights has rarely involved scientists in recent decades, so we do not have more accurate scientific data.

ps: Although there are legends that a cat can fall from the 46th floor and survive, this is an unscientific case, because the cat first fell on a tree canopy and finally fell to the ground. .

When a cat falls, it is a subject that scientists have always been interested in. This involves physics and biology, and scientists in both disciplines have done a lot of research on this phenomenon.

Because it involves a very difficult concept of physics-the law of conservation of angular momentum. Therefore, Chinese science popularization in this area is also rare. I will try my best to explain this matter in plain language.

The cat’s righting reflex[3] (righting reflex) refers to the cat’s orientation itself when falling from a height, and then landing on all fours. This is an innate ability. This reflex begins to appear at 3-4 weeks of age and completes in 6-7 weeks. Cats are able to do this because they have an extremely flexible skeleton and do not have a functional collarbone. Cats without tails and bobtail cats also have this ability, because cats mainly maintain angular momentum conservation by stretching their hind legs, and the tail is actually rarely used to complete this reflection.

cat touch the ground falls from a height

Let’s take a look at the research history of cat righting reflex, and by the way, add some biological knowledge to my answer to explain cat righting reflex under the topic of physics. If you have read it before, it should be my answer.

The first to appear is Maxwell. Well, it’s the Maxwell who proposed Maxwell’s equations.

When Maxwell was at Trinity College, he discovered that a cat can always keep the soles of the feet on the ground when falling from a height. So the physicist started an experiment. After many experiments, Maxwell discovered that when a cat falls from a height of less than 5 cm The soles of the feet do not touch the ground first (subsequent further research by scientists found that this height must reach 30 cm to ensure the safety of the cat). But he was still very happy to write to his wife to show off the discovery.

With the development of photography technology, a French scientist named Étienne-Jules Marey also became interested in this phenomenon. In 1882, Marais invented a camera gun that could take 12 consecutive photos per second, and all the images were recorded on the same photo. So we have this famous photo

Then Marais proposed the first explanation. Since this document is very old, I did not find the complete original, so I will quote the description from the English Wiki.

The cat uses its own inertia to adjust its posture. The force generated by the contraction of the spine muscles first acts on the forefoot. At this time, the forefoot is compressed short and is close to the neck. Its moment of inertia is very small. The rear foot extends almost perpendicular to the axis of the body, generating another moment of inertia, which rotates The direction is opposite to the former. In the second stage of the movement, the posture of the front and rear feet are opposite, and the inertia of the front feet provides the pivot point for the rear feet.

We can see that this explanation is very consistent with the posture shown in the picture above. However, many physicists still believe that the reason why the cat completes the first landing is because the person releasing the cat exerts force in advance, and the cat uses the releaser’s hand as the lever to complete this action. However, one of Marley’s views has been recognized by everyone, that is, air resistance does not help the cat’s righting reflection.

So why do other physicists question it, because it involves a physics concept called conservation of angular momentum.

The law of conservation of angular momentum is one of the basic laws ubiquitous in nature, and essentially corresponds to the invariance of space rotation. Physics is interpreted as reflecting the general law of the movement of the mass point and the mass point system around a point or an axis; reflecting the mass point and the mass point system that are not affected by external forces or the resultant moment of the external forces on a fixed point (or fixed axis) is always equal to zero The universal law of (or axis) movement.

The simple description of angular momentum is that when a particle rotates directionally along a certain axis with a certain radius, it will produce vector angular momentum. The judgment method is to make a fist with the right hand, with the index finger facing the direction of movement, and the direction of the thumb is the direction of angular momentum. That is what it looks like in the animation.

The expression of the angular momentum formula looks like this

Why does the cat always touch the ground when it falls from a height?

The application of conservation of angular momentum in life is that when a person walks, he has to shake the arm on the side of the body that is different from the thigh that he steps. Because the angular momentum generated by the leg needs to be offset by the angular momentum in the opposite direction, so turn It will be uncomfortable when walking. Therefore, physicists at the time believed that when the front legs of a cat turned down, the hind legs should be turned up. As a result, another misinterpretation that has been circulated to this day has been produced, that is, the angular momentum generated by the cat’s tail when the cat falls offset the angular momentum generated by the front body, so the cat landed on all fours. The popular explanation is that the tail is in this process. Has a very big effect. If you look closely at Marley’s photos, it really looks a bit like that.

Although the cat’s tail is proven to help balance the cat’s movement, later experiments have shown that tailless cats can also perform this action, but we still can’t completely rule out the role of the tail. We can only say that it is in the righting reflex. Little help or almost useless.

In 1969, Kane & Scher, an applied mechanics physicist from Stanford, published a research report. They divided the cat into the front half and the back half, and used a cylinder as a model for discussion.

Now this physical model is accepted by most physicists and biologists.

The animation display looks like this:

When a cat falls from a height, the vestibular structure in the cat’s inner ear will perceive its direction.

So the cat decided to walk in three steps.

1. Bend your body and bow your waist, so that the front and back parts of the body will rotate along different axes.

2. Shrink the front legs to reduce the moment of inertia of the front half of the body, and extend the rear legs to increase the moment of inertia of the back half of the body so that they can further rotate forward (rotate 90°), while the back half of the body rotates in the opposite direction It is smaller (as low as 10°).

3. Unfold the front legs and contract the back legs so that they can further rotate the back half of the body, while the front half of the body rotates at a smaller angle in the opposite direction.

This process can reasonably solve the law of conservation of angular momentum in physics. Because in the 1894 interpretation, the coordinate system of the physical model was set up wrong, and the wrong axis was selected. They chose the horizontal and vertical axis of the cat’s body for physical explanation, believing that this process violates the law of conservation of angular momentum. But I did not expect that the cat is a very soft organism with a special bone structure. The righting reflection can be completed by bowing the waist. The newly constructed physical model is as shown in the animation. The cat has formed three angular momentums that happen to form a complete vector triangle by bowing the waist. This follows the law of conservation of angular momentum, which allows the cat to complete the righting reflection by arching the waist and stretching the front and rear legs without too much effort. It is explained in terms of physics and biology.

Show this process with pictures like this:

Experiments conducted by the U.S. Air Force under weightless conditions show that cats cannot make righting reflexes under weightless conditions. In this case, the cat will not land on all fours after falling.

Finally: Please don’t try with your cat at will. If you must try, the righting reflex starts to appear at 3-4 weeks of age and will be perfected at 6-7 weeks of age. The cat used must be over this age. And need to maintain the height above 30cm, but it is best not to exceed 1 meter, it would be better if you can lay a thick cushion.


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