In fact, the “knees” of those students who think they are bent backwards are not actually knees at all. First, the knee is physiologically defined as the junction between the thigh and calf. This can be clearly distinguished on humans. Many animals seem to have such a structure at the joints of their legs, but they cannot simply and crudely transfer human structures to animals.
The bones in human thighs and calves are called “femur” and “tibia”, respectively. For animals such as cattle, the “thigh” you think is actually the “tibia”, so it should correspond to our calf. And their real thighs, that is, the “femur” is located above the “tibia” and closer to the hip area. Therefore, the real knee was hidden very close to the body. The same is true for chickens and ducks. The “chicken thighs” and “duck thighs” that classmates usually love are just their calves.
So what are those structures that we mistakenly think of as “knees”? In fact, they are equivalent to our ankles, and the so-called “low legs” are part of the soles of the feet. Therefore, they are actually walking on their toes, which is why they are called “toe walking animals”. And we humans and other primates and other animals walk on the soles of their feet, so they are called “tadpoles.”
Why does an insect fall from a height and fall to death?
First, the injury to a fall comes from the net value of speed, and does not depend on the ratio of body size to fall height. It is unreasonable to enlarge the speed proportionally or the height of the fall.
Second, insects are much stronger than we think. We know that the density of matter is approximately constant, and the mass of an insect is inversely proportional to the third power of its size. And gravity will act on the material’s force area, which is inversely proportional to the power of size. In other words, the force per unit area increases with mass. Assuming that humans are reduced by a factor of 100, in fact, the strength of the human body must be increased by a factor of 100, which is exactly the factor that limits the size of species on the planet.
Another factor is air resistance. In the low-speed region, the air resistance is approximately proportional to the area of the windward side, that is, proportional to the power of the second power, and the weight is proportional to the power of the third power. Therefore, for insects that are one hundredth the size of humans, air resistance has a strong effect on them, and their fall effect is equivalent to the effect of dropping humans at 100 times the air resistance.
For most insects, another factor is that most of them have strong physical strength. Their body structure and materials are actually quite resistant to falling.
Under the combined effect of these three factors, a fall is not a great threat to insects.
Why is a tungsten bulb a pear shape?
When this lamp is in operation, the filament temperature is very high. Metal tungsten will sublimate at high temperature and adhere to the inner wall of the bulb. Therefore, the bulb is made into a pear shape and filled with a small amount of inert gas. The sublimated tungsten can be rolled up with the gas convection and attached to the neck of the bulb , You can keep the glass transparent, so that the brightness of the bulb is not affected. And because the early glass was made by blowing, this shape is not only easy to blow, but also saves raw materials. In addition, the pear-shaped surface has a certain curvature, which can increase strength and withstand greater pressure.
Why can’t I dial 110 if my mobile phone doesn’t have signal?
The reason is simple. We know that after the mobile phone is normally powered on, it will first detect if there is a SIM card, and then search for nearby operator base stations and networks for registration and authentication. The presence of a SIM card does not affect the normal operation of the RF module of the mobile phone. Generally speaking, the SIM card is more like a “gate card” that “connects” with the corresponding operator and base station.
In most cases, when the mobile phone displays no signal, it reflects that there are no corresponding base stations and networks around. However, this does not prevent the mobile phone’s RF module from receiving signals from other nearby operators and base stations. And emergency numbers like 110 and 120 have higher priority and do not need to register to complete the authentication between the mobile phone and the network. Generally speaking, it does not matter the difference between operators. Therefore, in most cases, these emergency numbers can be reached when the mobile phone has no signal.
However, if you are in a place like Shenshan Old Forest where there are really no base stations, the emergency number will not work. At this time, change your method and use a satellite phone!