Quite ask sth

When we walk, we usually just focus on moving our legs and often don't realize that our arms are also involuntarily swinging back and forth in coordinate with our legs. But since walking only requires the use of our legs, why doesn't the body save the energy expended by swinging our arms? Scientists also thought this way for a long time, considering the swinging of arms during walking as an evolutionary leftover behavior and didn't think it had any significance.

However, recent studies have shown that this way of walking is actually the most energy-efficient. Researchers had participants complete three sets of actions: 1) normal walking, as a control; 2) walking while keeping the arms still; 3) walking with the same leg and arm moving together.

The results found that walking with the arms still consumed 12% more energy than normal arm swinging, and walking with the same leg and arm moving together consumed an additional 26% of energy. So, it turns out that our normal way of walking is actually the most energy-efficient.

This result is also easy to understand. When we walk, our body produces natural swaying, which causes the arms to swing like pendulums, aiding in the coordination of walking and reducing the overall swaying of the body. Intentionally controlling this natural movementon the contrary increases energy expenditure.

Why do human hair grow so long?

This question, like many related to evolution, does not yet have a definitive answer, and there are only some controversial speculations at present.

First is the aquatic ape hypothesis, where researchers suggest that human ancestors may have once lived in water. Long hair, when spread out in water, allows infants to easily grasp and return to their mothers in dangerous situations, increasing the probability of survival. However, this hypothesis has not yet been accepted by the scientific community. Another sexual selection hypothesis suggests that hair, apart from being "attractive," has no practical use. This is like the mane of a lion or the tail feathers of a peacock, traits that have been selected for attracting mates and are used as a judgment of health during mating.

There is also the view that thick, long hair is a good insulating layer, reducing heat loss from the head and helping to endure cold climates. Some suggest that after humans began to walk upright, the top of the head receives more direct sunlight, and the presence of long hair protects the head and back from ultraviolet damage. There is even a theory that human hair is an extension of sensation, although our hair is composed of dead cells, they are connected to the scalp, and when hair is pulled, we can feel it, thus allowing us to react more promptly to potential dangers.

The last theory does not acknowledge any direct benefits of hair to humans but rather that it just piggybacks on other genes. In fact, the genes controlling hair traits are not singular but are related to many genes. Among these genes, there may be some that are truly beneficial for survival and favored by natural selection, and the genes controlling long hair traits may just happen to be close to them or have a direct or indirect promoting effect on the expression of these genes, thus being preserved to this day.

However, according to the current trend of hair loss in modern people, long and thick hair may become a rare trait in the future (joke).

Why do earphone cables always tangle on their own?

When you're annoyed and want to listen to music to relax, you take out your earphone cable from your pocket only to find it has become a difficult-to-unravel mess, which makes you even more frustrated. Why earphone cables love to "cause trouble" is also a mystery that physicists find very interesting. However, even before the invention of earphone cables in the 19th century, scientists had proposed the "knot theory" to analyze the phenomenon of ropes knotting, which is to use mathematical methods to study the configuration of curves in three-dimensional space, and finally summarize each type of knot into a mathematical model.

Later, physicists specifically studied this phenomenon. They placed ropes of different lengths in a box and repeatedly inverted them for 10 seconds, trying out different box sizes and inversion frequencies. After 3,000 repetitions, they concluded that the degree to which ropes spontaneously knot is mainly determined by the length of the rope. Ropes shorter than 46 centimeters will not knot no matter how the box is turned; as the rope length increases to two meters, the probability of knotting increases to 50%. However, ropes longer than two meters are less likely to knot because these ropes are squeezed into boxes with limited space and have difficulty moving freely. Generally, earphone cables are between 120 to 160 centimeters in length, so they often end up knotted in half the time.

To deal with this situation, you can choose to properly fix the earphone cable in the earphone case (as if I didn't say anything), you can also choose a smaller container to hold the earphones to limit their movement, or you can Simply cut into wireless headphones completely worry (joke).

Can sand from the desert be used to build houses?

Building materials such as sand used in concrete generally come from rivers and not from the desert. You must be curious why the vast amount of sand in the desert is not utilized? With the current high demand for building materials, if this were developed, it might even alleviate sandstorms, killing two birds with one stone.

It sounds nice, but practical application is not that simple. The sand in the desert is blown by the wind and baked by the sun every day, unlike river sand that "lives comfortably," and has been ground too finely to meet the strength requirements for construction materials. In addition, desert sand contains more impurities, especially high alkalinity, which can easily react chemically with other components in building materials, making the building structure unstable. River sand, on the other hand, has been washed and scoured by water flow for a long time and is relatively purer and cleaner, saving some complicated washing and screening processes. The carrying action of the water also makes the river sand particles more rounded and smooth, resulting in more uniform stress when used as building materials.

In addition to the unsuitability of the characteristics of desert sand for building materials, the cost of labor and resources is also increased by transporting sand from remote deserts, so they are generally not chosen for making concrete and other building materials.

However, there are also researchers studying how to develop and utilize sand from the desert. After conducting experimental analyses on the sand from the Tengger Desert and the Mu Us Desert, they believe that with appropriate treatment and added to building materials at the right ratio, there is still feasibility in using these sands. It's just that using desert sand is not as cost-effective as transporting river sand.

If you can't build a house, why not use it to make sand sculptures (serious face)?

Why can parrots speak like humans?

Parrots, these clever little creatures, bring us a lot of joy with their ability to mimic human speech. But have you ever thought that parrots, unlike us, do not have soft lips to make flexible mouth shapes, so why can they speak like humans?

Parrots do have this talent, but the structures they use to exert their talent are different from ours. When humans speak, we use our larynx and vocal cords to produce sound, and then change the tone and intonation through the movement of our mouth shapes and tongues. Parrots, like other birds, produce sound through their syrinx. They can control the muscles on the walls of the syrinx to shape different sounds. Extending or retracting their necks to varying degrees or opening and closing their beaks can also play a Auxiliary regulation role. Parrots have very flexible control over their syrinx, thus they can accurately replicate the sounds they want to imitate. When they make sounds, you can clearly see the rise and fall of their chests, which is actually controlling the syrinx.

Vowels (A, E, I, O, U), which require us to significantly control our mouth shapes, parrots can produce by controlling the movements of their tongues and beaks. Some more difficult sounds, such as plosives, which even humans might not be able to pronounce well, parrots can produce through their trachea, sounding like hiccup noises.

The area of the parrot's brain responsible for the language system is also quite complex, not only having a core system for producing sounds but also a special shell system. Parrot chicks from birth are constantly learning the sounds around them; they have a strong desire to express themselves and like to "group chat" with their peers in the wild. The ability to mimic other birds' calls is also one of their criteria for mate selection as adults. However, after becoming pets of humans, the only person they talk to is their owner, and in their view, your voice may just be a strange bird call, and yet this has not stopped them.

Parrot: "What kind of bird language are you speaking? Why would a repeater make things difficult for another repeater?"