Physics and survival, physics and life are more, find it yourself.

Example: The human body is not only the research object of life science, but also the research object of physical science. Our human body is a machine equipped with full application of physical knowledge, and many parts or organs of it are the embodiment of the application of physical knowledge.

1, breathe

The human respiratory system is not only closely related to the atmosphere, but also makes use of the relationship between gas pressure and volume in physics.

When the inspiratory center is excited, the diaphragm between the chest and the abdominal cavity is contracted by the phrenic nerve, the volume of the chest cavity is expanded, and the air pressure inside is also expanded, making it lower than the external atmospheric pressure, so the external air flows into the lungs from the nostrils and the mouth under the action of atmospheric pressure and enters bubbles. Exhale is just the opposite, because the chest volume decreases, the air in the lungs contracts, the internal pressure is greater than the external pressure, and the gas is exhaled from the lungs.

2. Eyes

Eyes are the windows through which people observe the world. It uses the principle of convex lens imaging in physics to see objects with different distances.

The eye consists of cornea, lens-like fluid, vitreous body and retina. Their combined action is equivalent to a convex lens. After the light emitted by the object is refracted by the convex lens of the eye, an inverted and reduced real image is formed on the retina, which stimulates the photoreceptor cells distributed on the retina and is transmitted to the brain through the optic nerve, so we see the object. The eyes can not only see near objects, but also clearly see distant objects. When the object distance changes, the focal length of the convex lens can be changed by changing the curvature of the lens surface. Therefore, the eye is actually a delicate zoom system. Of course, the function of the eye to adjust the focal length is limited.

Myopia or hyperopia cannot be adjusted by itself, so it must be adjusted with a suitable concave lens or convex lens to achieve the purpose of seeing the surrounding objects clearly.

3. Teeth (plural of tooth)

Teeth are used to chew food. People's teeth are mainly composed of incisors, canines and molars, and the body division of labor is very clear.

(1) front teeth: There are four pairs. They are flat and wide, like a knife, specially used to bite food. The cross section of the front teeth is very narrow, like a blade. With the same strength, they can produce more pressure and cut food easily.

(2) Canine teeth: There are two pairs on each side of the mouth, which, like hooks, can also produce great pressure. Its main function is to chop up food.

(3) Mortar teeth: particularly thick and round, with some grooves on it. It grinds food by pressure and grinding just like soybean milk. Whether it is whole or shredded food, it must be processed by molars and swallowed into the esophagus.

4, vocal cords

Vocal cord is an important organ for human voice. Without vocal cords, people can't speak.

Sound is produced by the vibration of objects. When we speak, the vocal cords vibrate, and this vibration propagates through the medium of air to form sound waves.

5. Ears

Ear is an important organ for receiving sound, which is mainly composed of auricle, ear canal, tympanic membrane and auditory nerve. The sound produced by the vibration of an object propagates in gases, liquids and solids in the form of sound waves. This sound wave is first collected by the trumpet-shaped auricle, then transmitted to the eardrum through the ear canal, making the eardrum vibrate, and then transmitted to the brain through the auditory nerve, so that we hear the sound.

6. Skin

Skin is the body's first line of defense. It consists of epidermis, dermis and subcutaneous fat layer.

The subcutaneous fat layer covers the surface of the human body like a quilt, which is very elastic. When the human body is collided, it has a buffering effect, which can prevent the internal organs and bones from being directly infringed by the outside world.

The most prominent physical functions of skin are heat dissipation and heat preservation. When the outside temperature rises, the blood vessels of the skin dilate and congestion, and the blood carries body heat to the air through the skin. At the same time, sweat glands also secrete a lot of sweat, which takes away excess heat in the body through evaporation of sweat. When the outside is cold, the skin blood vessels contract, the blood volume decreases, the skin temperature decreases, and the heat dissipation slows down, which helps to keep the body temperature constant.

7.fingerprints

Different people have different fingerprints, so they can identify who they are. But the most prominent physical function of fingerprints is to increase the friction when we hold objects in our hands. The magnitude of friction is not only related to the magnitude of pressure, but also related to the roughness of contact surface. If we don't have fingerprints on our hands, it will be difficult to pick up an object with a smooth surface. We should also take other measures, such as putting a cloth between our hands and objects to increase friction, so that we can easily pick up objects.

8. joints

Joint is an important connection mode and precise connection structure of human bones, and it is a clever fulcrum of bone lever movement. The bone surface (articular surface) at the joint of each bone is very smooth, and the surface is covered with articular cartilage composed of hyaline cartilage to enhance smoothness and reduce friction.

9. arm, arm (plural of arm)

People's arms bend forward slightly when they relax. We can tighten the muscles in front to bend our arms forward, or we can tighten the muscles in the back to straighten our arms. The forearm of the human body is essentially a lever, and the elbow joint is the fulcrum of this lever.

When we bend our forearms, the biceps femoris in front will tighten, which will bend our forearms and relax the triceps femoris in the back.