If you throw a cat upside down, the smart ones will land on all fours, but the stupid ones will...

Cats are all masters of parkour. Even if they accidentally fall while climbing walls and flying over rooftops, they can always land safely in most cases. That’s why people often say that “cats have nine lives”.

Although it is impossible for cats to really have nine lives, people's praise for cats also shows that cats do seem to have special skills. No matter in which posture they fall, they can always land on all fours, so they are not easily injured.

Smart cats always land on all fours. GIF from | TikTok @Xizi1313

Stupid cat...

How do cats manage to land safely? Many scientists are very interested in this "falling cat" problem.

The most famous scientist among them is Maxwell. This English mathematical physicist, who is known as "second only to Newton and Einstein", not only has world-renowned achievements in the field of electromagnetism, but is also very interested in the problem of falling cats. After many attempts, he found that cats can always twist their bodies in a flash and land safely.

Of course, Maxwell's scientific experiments were not rigorous enough. In 1984, French scientist Marey invented a camera gun that could take 12 photos in a second.

Thanks to this new camera technology, people can finally see the entire process of the cat falling: the cat with its limbs facing the sky deftly flips 180° in the air, and then lands safely.

The process of a cat falling to the ground, reading order is from right to left (Image source: Reference [1])

This difficult action is just something we humans can "watch", but for cats it is as easy as eating and drinking. This is because a biological reflex called "righting reflex" is deeply engraved in the cat's genes.

People who fall off a cliff usually fall on their backs, their limbs dangling in panic but unable to move.

If we also possessed this skill, I'm afraid the cliff-falling scenes in martial arts novels and TV dramas would have to be rewritten.

One of the cat's special skills: righting reflex ✦

The righting reflex is a talent that cats are born with. Generally, kittens at 3 weeks old have a preliminary righting reflex, and kittens at 6-9 weeks old have already mastered this skill to perfection.

It is precisely because of this unique skill that cats can overcome the law of conservation of angular momentum in the air and instantly adjust their bodies from an unfavorable posture to a safe landing position with all four legs facing downward.

So, what is the conservation of angular momentum?

Simply put, angular momentum is a physical quantity used to describe the rotation state of an object, which is related to the rotation speed and rotation radius. The faster the object rotates and the larger the rotation radius, the greater its angular momentum.

The conservation of angular momentum means that when an object is in a stable rotation state or a stationary state, it will continue to rotate or remain stationary without the help of external forces, that is, the angular momentum always remains unchanged.

Cats have hundreds of bones and muscles in their bodies, and they have strong control over every part of their body. Therefore, cats can flexibly twist their bodies in the air, and with the help of weak air resistance and gravity, they can successfully complete the righting reflex and break the constraints of conservation of angular momentum.

In 1969, Stanford physicist Kane gave a convincing explanation of the principle of cats' righting reflex.

The process of a cat's righting reflex (Image source: Reference [2])

He divided the cat's righting reflex into three steps:

The first step is to bend your body

When a cat first falls on its back, it will try to arch its body as much as possible.

If the cat is regarded as a whole, it will not be able to rotate in the air; but if the front and back of the cat's body are regarded as two parts that can rotate independently, then there will be a lot of room for movement.

Step 2: Adjust the direction of the forelimbs

Cats adjust the direction of their front limbs by twisting their bodies. When twisting, the front and back parts of the body twist in opposite directions. At the same time, cats will try to shrink their front limbs and stretch their hind limbs.

According to the law of conservation of angular momentum, the rotation radius of the front half of the body decreases, the rotation speed increases, and it is easier to rotate; while the rotation radius of the back half increases, the rotation speed decreases, and it is more difficult to rotate.

In this way, when the front half of the cat's body has turned nearly 180°, the back half of the body has only turned about 10° in the opposite direction.

In this way, the front half of the body can be adjusted to a posture with the front limbs facing down while the back half of the body is kept almost unchanged. In this process, the angular momentum generated by the front and back parts of the body cancel each other out, and the conservation of angular momentum still holds.

Step 3: Adjust the direction of the hind legs

The cat will then twist its body in the opposite way, stretching its front limbs as much as possible and contracting its hind limbs, making the back half of its body easier to rotate than the front half.

This allows the back half to be moved into a hind-legs-down position while the front half of the body remains almost still.

In short, cats use their strong control over their muscles and bones to "break down" their bodies into two different movement units.

The two motion units can simultaneously perform twisting rotations in opposite directions, which can ensure that the angular momentum remains unchanged while adjusting the body to a posture with all four limbs facing downward.

Motion decomposition of the falling cat process (Source: Reference [3])

Scientists also found in the study that cats in a state of weightlessness cannot twist their bodies smoothly, which shows that gravity plays an important role in the completion of the righting reflex.

NASA's falling cat experiment (Source: Wikipedia)

After all, there is no concept of "ground" in a weightless environment.

Cat's special skill 2: Limbs and trunk that can effectively cushion the impact ✦

Can you land safely by flipping your body in the air? No, no, cats have another trick up their sleeves - they use the movement of their limbs to reduce the impact of falling and achieve efficient cushioning.

A cat's limbs are like a set of flexible mechanical linkage structures that can be folded and stretched stably and quickly, while the well-developed muscles act like dampers and attenuators, providing strong support and cushioning for the cat's trunk.

The structure of a cat’s thigh (Image source: Reference [4])

Cats' landing cushioning skills are very efficient and can effectively prevent themselves from being hurt by the impact. Parkour masters also use a similar method when jumping from a high place, bending their legs at the moment of landing to reduce the impact.

However, they then need to roll on the ground so that they can completely dissipate the kinetic energy of the fall.

Rollover buffer

The researchers also designed a bionic spacecraft landing cushioning device based on the cat's thigh structure, which can achieve the safe landing of the spacecraft.

Spacecraft bionic landing bracket (Image source: Reference [4])

Cat's unique skill 3: exquisitely structured cat paws ✦

The pads of cats' paws are not only thick, but also feel soft and elastic. This is mainly because there is a three-dimensional network structure composed of collagen fibers and elastic fibers in the pads, and the chambers of these network structures are filled with a lot of fat.

The microstructure of a cat's paw and its equivalent simplified structure (Source: Reference [5])

This sophisticated cat paw structure is very suitable for cushioning and energy absorption: the mesh skeleton can provide stable support when the paw touches the bottom, allowing the cat to firmly grasp the ground; the friction between the mesh skeleton can consume part of the impact force; and the soft and elastic fat particles can provide cushioning.

Therefore, this unique function of cat's paw can help cats land safely. Scientists have also developed a cat paw bionic composite material based on the multi-layer structure of cat's paw.

Microstructure of artificial cat paw bionic material (Source: Reference [5])

It is precisely because of these three skills that cats can avoid being injured or killed when they accidentally fall.

However, cats are fragile creatures in front of humans. Please remember that they accompany us every day. If you have a cat, treat it well from beginning to end, be gentle, and do not abandon or abuse it. It is strongly recommended to adopt instead of buying!

If a cat has no tail, will it still land on all fours when it falls? ↓ ↓

References:

[1] Photographs of a Tumbling Cat. Nature 51, 80–81 (1894) doi:10.1038/051080a0

[2] How does a cat fall on its feet?, The New Scientist, vol. 7, no. 189 (1960), pp. 1647-9.

[3] TR Kane & MP Scher, Department of Applied Mechanics. Stanford University, California, “A Dynamical Explanation Of The Falling Cat Phenomenon,” Int. J. Solids Structures. 1969. Vol. 5. pp. 663 to 670

[4] Yuan Yingnan. Research on a new concept manned lunar lander based on cat-like legs[D]. Nanjing University of Aeronautics and Astronautics, 2020.

[5] Wenjiang Lu, et al. Hierarchical network structural composites for extraordinary energy dissipation inspired by the cat paw[J]. Applied Materials Today. 2021: 101222.

END

Review expert: Ran Hao, well-known popular science writer.

Tadpole Musical Notation original article, please indicate the source when reprinting

Editor/Xiao Xitushuo