# Animals also understand physics

If an animal accidentally falls from the top of a tree in the process of foraging, they will certainly not know that it is the gravity of the earth. However, the lack of theory does not mean that these animals will not use the difficult laws of physics to practice. After we have mastered some physical knowledge, we can understand some of the animal “magic skills” and life habits that make humans feel incredible.
This animal will “light work”

On the surface of the water, an animal is walking leisurely. It has a slender figure, and its six legs are steadily stepping on the surface of the water. There is no fear of getting wet or sinking in the water. It is a water strider. Why doesn’t the water strider sink like most animals because of gravity?
Anyone who has studied physics knows that if the weight of an object is less than the buoyancy produced by a liquid, it will not sink. Therefore, if the water strider wants to walk smoothly on the water, it needs to have very large buoyancy. As the Greek scientist Archimedes pointed out, the buoyancy of an object is equal to the gravity of the object expelling liquid when it sinks. However, it is on the outer surface of the liquid, not in the liquid, and different calculation rules need to be applied.
Regardless of fallen leaves or water striders, when it falls on the surface of a liquid, there are two main factors that determine its buoyancy: one is the strength of the tension generated by the liquid surface, and the other is the biological contact. The surface area of ​​the liquid.
The so-called tension of a liquid means that its surface will be as tight as a trampoline and have elasticity. The surface tension of water is very large. As long as the water strider’s feet are flat on the surface of the water and the contact area with the water can reach one square centimeter, the buoyancy generated is sufficient to hold the light water strider. This is why most water striders can safely walk or even jump on the water.
Being too “fat” can fly high and jump long

In the early 20th century, some scholars used traditional aerodynamic laws to prove that bumblebees are impossible to fly because their bodies are too fat and their wings are too small to generate thrust that exceeds the body weight of bumblebees. In fact, not only can the bumblebee fly normally, but research has found that some wasps can fly more than 100 meters higher than Mount Everest. So, what is wrong with these scholars?
It turned out that the model they used was too simple. They assumed that the wasp did not flap its wings, and was as stiff as an airplane wing, and ignored the trajectory of the wing tip of the bumblebee.
Compared to other insects, the bumblebee flaps its wings more frequently in order to generate lift, up to 150 times per second. In addition, the trajectory of the bumblebee’s wing tip is not a simple up and down movement, but a “8” or “q”-shaped trajectory. When the hornet flaps its wings down, this movement trajectory An air vortex called a leading edge vortex will be created on the leading edge of the wings. The existence of this vortex can cause a low-pressure area above the wasp’s wings, similar to a small cyclone, so that the wasp can obtain upward lift.
Spiders are good at using static electricity

There is a very popular superhero under the umbrella of Marvel, and he is Spiderman. Spider-Man has a strong climbing ability, can climb on the outer edges of tall buildings with bare hands, and can even shuttle freely on the ceiling. When fighting with enemies, it can spray spider silk to firmly stick to each other. Although Spider-Man does not exist in real life, in the animal kingdom, there is a realistic version of “Spider-Man”-Spider.
The mystery of spiders is hidden under their feet. From a mechanical point of view, when two solid surfaces are close to each other, the interaction force between them is very complicated, including van der Waals force, electrostatic force, dipole force, capillary force, etc. There are a large number of bristles on the soles of spiders. When they interact with the molecules on the surface of the object, they will produce van der Waals forces. Van der Waals force is a kind of weak electromagnetic force generated when neutral molecules are very close to each other. The superposition of a large number of van der Waals force is enough to support the weight of the spider.
In addition to crawling, spiders are also very capable of preying. Many people may think that the web of spiders is sticky. When small moths, mosquitoes or other animals hit the spider web by mistake, they will become the spider’s dish. However, these little animals are not all caught by spider webs by accident.
Invisible hippocampus

The pygmy seahorse is only 2.5 cm long and is called “the slowest fish in the world”, walking only 1.5 meters per hour. If there is a 100-meter sprint underwater. These sharp-headed, curly-tailed creatures will take almost three days to reach the end, but from a physics perspective, their slow lifestyle also makes sense.
In the warm Caribbean waters, pygmy seahorses and copepods that most fish like to eat live, which is a millimeter-sized transparent crustacean. In order to avoid the powerful enemies all over the ocean, the copepods have sensitive antennae and can detect the smallest liquid movement. Once they detect the movement of the water, the copepods can swim 500 times the distance of their bodies in one second. Can only run 30 times the distance of the body in a second.
Faced with the prey that can be called a runner-up champion, the slow seahorse must crept on his feet to eat a good meal. Fortunately, the head of the hippocampus is a long and narrow triangle, which can better resist the interference of liquid resistance, so that the water will not vibrate too much.
Dog’s spin-drying method

Throw the stick into the water, and a well-trained dog will jump directly into the water and pick it up. The problem is that the dog’s fur is very thick. After being wet, the body will be very bulky. A 27 kg wet dog’s fur will contain 0.4 kg of water, and the dog will consume 20% of body heat to remove water. So, how should dogs keep themselves dry?
Using body heat to heat the air and evaporate water requires a lot of energy. Therefore, the dog chose another way-to take the initiative to dry himself. The water-throwing action of the dog starts from the head, and the energy wave takes the head as the reference point and spreads to other parts of the body. The larger the head twist, the larger the amplitude wave. When a dog uses “spin dry” Dafa, although the body shakes the same frequency as the cortex, the body cannot be twisted as much as the cortex. This is because the cortex is more relaxed. When the body is shaken violently, the fur is shaken more than the body and the head, and the acceleration will increase as a result. Such an action is as powerful as swinging a whip.