Newton, a physicist, found that all substances attract each other, which is called gravity or universal gravitation. This attraction has a simple relationship with the quality and distance of substances: the more substances, the greater the quality and the greater the attraction; The closer the distance between substances, the greater the gravity. Even between two people, there is gravity; When people live in a space with minimal gravity, the gravity between people will bring everyone's body closer; The gravity of two big fat people is greater than that of two children at the same distance. Gravity dominates the motion of stars in the universe. For example, the moon goes around the earth, which is caused by the gravity between the moon and the earth.

Every planet contains a lot of matter, such as the earth. To write its mass in kilograms, you have to add 24 zeros after 6! In the universe, the earth is just a relatively small planet. There are too many substances on the earth, and the gravity is great, which is why we can't fly out of space standing on the ground. Because all the substances on the ground are attracted by the gravity of the earth, it is difficult for the ground to "tilt" and the mountains should not be too high, because the gravity of the earth will pull the substances on the peaks to the center of the earth, so the earth is round. The mass of the moon is only one eightieth of that of the earth, so its gravity is much smaller than that of the earth, and the mountains on the moon are much higher than that of the earth (figure 1).

According to the above theory, the greater the mass of a planet, the more round it is. On the contrary, if the mass is small and the gravity is small, the star may not be round. In fact, in addition to the nine planets, there are many asteroids with very small mass in the solar system. Their shapes are not very regular, just like a big stone.

2. Why is the trunk round?

In the process of observing nature, I happened to find that the shape of the trunk is almost round-an empty cone. Why is the trunk conical? What are the benefits of a conical trunk? In order to discuss these problems, I made more in-depth observation and analysis.

With the help of my tutor, I consulted relevant materials and learned that the stems of plants have the functions of supporting plants and transporting water and other nutrients. The stems of trees are mainly composed of vascular bundles. The supporting function of stem is mainly borne by wood fibers in xylem. Although the stems of woody plants will become thicker year by year, in a certain time range, the number of woody fibers in the stems is certain, that is, the cross-sectional area of the stems is certain. Then, based on the assumption that the cross section of the trunk grows into different shapes, we design experiments to explore the reasons and advantages of conical trunk.

Through experiments, we find that when the cross-sectional area and length of (1) are fixed, the vertical supporting force of triangular columnar objects is the largest and the lateral bearing capacity is the smallest; The vertical supporting force of cylindrical objects is not as good as that of triangular cylindrical objects, but the lateral bearing force is the largest; (2) For trunks with the same mass and different shapes, the short conical trunk bears the largest wind force; (3) Wind is a natural phenomenon, which affects the cross-sectional shape and height of trees. The approximate cone-shaped trunk has a low center of gravity, and the huge root system is connected with the earth, so the center of gravity drops lower and the stability is greater; (4) The cross section of the trunk is round, which can reduce the damage, has stronger mechanical strength and can resist the wind attack. At the same time, under the action of the wind, the bending degree of the trunk is similar everywhere. No matter which direction the wind blows, the resistance of the trunk is similar, and the trunk is not easy to be damaged.

The above experiments reflect the laws of nature, and nature enlightens us: (1) A columnar object with a triangular cross section has the greatest vertical supporting force, and its shape can be used in buildings, such as angle steel; (2) A circular object with a circular cross section has the largest lateral bearing capacity, and similar building materials can be found everywhere, such as TV towers and telephone poles.

In the process of observation, experiment and analysis, I gradually explained and revealed the mystery of conical trunk, increased my knowledge, and combined my knowledge with practice, which not only consolidated my knowledge, but also improved my interest in learning, and initially learned the scientific observation and analysis methods.

3. Window grilles In the cold winter, people close the door to keep warm in the house. When the indoor temperature is high, the water vapor in the air becomes hot. When they vibrate, they will condense when they touch cold glass. And some glass is smooth, some glass is rough, some glass is spotless, and some glass has a lot of dirt on it. So that the water vapor will be uneven when covered. In some places, there is more water vapor and the ice will be thicker. In some places, there is less water vapor and the ice will be thinner. Where the ice is thin, it will melt when it encounters a little heat and pressure. Just like when people paint, the color becomes darker when they use too much paint. If the pigment is used less, the color will be light; Where there is no pigment, it is the original color of the drawing paper.

In this way, all kinds of beautiful ice flowers on the glass window were "painted" Because water has surface tension, there is mutual tension between water molecules, and they tend to recombine towards the center of water. This is how the beautiful dew on the lotus leaf is formed. On the plane of the glass window, groups of water molecules also "exert force" in their own center. As a result of this effort, there are all kinds of very regular and beautiful patterns. These patterns are not necessarily pentagons or hexagons, but can be many other patterns. But no matter what pattern it is, it must be very neat and beautiful. How is it formed?