Physics is a natural subject with a long history. As an important branch of natural science, physical science not only plays an important role in promoting the progress of material civilization and deepening human understanding of nature, but also has an indispensable influence on the development of human thinking.

From natural philosophy in Aristotle's time to classical mechanics in Newton's time, and then to relativity and quantum mechanics in modern physics, all these are tangible manifestations of physicists' scientific quality, scientific spirit and scientific thinking. With the development of science and technology and the progress of society, physics has penetrated into all fields of human life.

When it comes to physics, some students find it difficult; When it comes to physical inquiry, some students feel unfathomable; Speaking of physicists, some students think they are not ordinary people. It is true that there are only a handful of physicists, but as long as you are diligent in observation, good at thinking and brave in practice and innovation, you will find that physics is around you.

As Marx said, "Science is experimental science, and science lies in arranging perceptual materials in a rational way". Physics is not only a discipline but also a science.

There are many physical phenomena in life, and many simple phenomena can be answered by what we have learned. For example: 1. The rearview mirror outside the driver's cab is convex.

By using the divergent function of convex mirror to light and the characteristics of upright, narrow and virtual image, the objects you see are small and the observation range is wider, thus ensuring driving safety. 2. The magnifying glass uses the imaging law of convex lens.

3. Myopic glasses use the refraction of light. 4. The money detector uses the fluorescence effect of ultraviolet rays.

Wait a minute. Even natural phenomena in nature are closely related to physics.

Rainbow is formed by the scattering of light. The gravity of the earth is due to the molecular gravity between objects and the earth.

It thunders in rainy days because of positive and negative elements. Wait a minute.

Physics exists around physicists. Galileo, an observant Italian physicist, took great interest in the swing of the copper chandelier hanging in the air in Pisa Cathedral when he was attending church. Later, after repeated observation and research, he invented the synchronization of the pendulum. In order to understand the essence of "God's wrath", Franklin, an American physicist who is brave in practice, risked his life to bring "God's fire" to the world with an ordinary kite on a day of lightning, thunder and rain, and invented the lightning rod. British innovation scientist Henry? Achar went to the post office to handle affairs.

At that time, a foreigner next to me took out a large edition of new stamps to cut and post on the envelope, but he didn't have a knife. I borrowed it from Aga, and Aga didn't have it.

The foreigner had a brainwave, took off the pin on the suit and tie, neatly pierced a circle of holes around the stamp, and then neatly tore it off. When the outsiders left, they left Aga with a series of profound thoughts, and therefore invented the stamp punching machine, and the stamps with tooth patterns were born. Archimedes discovered Archimedes principle in ancient Greece; German physicist roentgen discovered x-rays; ..... There are countless examples of physicists who have made great achievements in studying trivial matters around them.

Physics also exists around students. Today, all the amazing scientific and technological achievements of mankind, such as sheep cloning, internet, nuclear power plants, aviation technology and so on. All of them are based on the observation and research of trivial things around scientists in the early years.

In learning, students should establish scientific consciousness, focus on the overall situation, start from small things, gradually master scientific learning methods and train scientific thinking methods through observation, thinking, practice and innovation, and soon you will have the mind of a scientist, laying a solid foundation for your amazing development and beautiful life in the future. Physical Essay 2 The change and melting of the state of matter: solid → liquid endothermic solidification: liquid→ solid exothermic vaporization: liquid → gas endothermic liquefaction: gas→ liquid exothermic sublimation: solid → gas endothermic sublimation: gas → solid exothermic matter changes from one state to another, which is the first of all solid and liquid states of matter. The relationship between the two is that when a substance changes from solid to liquid, this phenomenon is called melting, and melting requires heat absorption, such as ice absorbing heat and melting into water. On the contrary, when a substance changes from a liquid state to a solid state, this phenomenon is called solidification, and solidification requires heat release, such as water heat release and solidification into ice.

These solids that change from solid to liquid are divided into crystalline and amorphous. Crystals have a melting point, that is, when the temperature reaches the melting point, they will melt (continuously absorb heat), and the temperature will not be higher than the melting point when melting, but will rise after complete melting. Amorphous crystals have no fixed melting point, so the melting temperature is uncertain.

When the crystal melts, the temperature is constant and there are three states. For example, when the ice melts, the temperature is 0℃, with ice in solid state, water in liquid state, and ice and water in solid state. Then there is the relationship between gas and liquid, and the substance changes from liquid to gas. This phenomenon is called vaporization, and there are two ways: vaporization and boiling. Evaporation occurs on the surface of the liquid and can be carried out at any temperature, which is slow.

Boiling occurs on the surface and inside of the liquid and must reach the boiling point, which is intense. Vaporization requires heat absorption, and liquids have boiling points. When the temperature reaches the boiling point, the temperature will not rise again, but it is still absorbing heat. When a substance changes from a gaseous state to a liquid state, this phenomenon is called liquefaction, which gives off heat.

For example, water vapor is liquefied into water and water is evaporated into water vapor. The methods to accelerate liquid evaporation are: 1. Increase the surface area of liquid; 2. Speed up the air velocity on the liquid surface; 3. Increase the temperature of the liquid; 4. Reduce the water vapor content of the surrounding environment so that it cannot be saturated (i.e. dry air. )

Finally, we don't often see the relationship between solid and gas. Matter changes directly from solid to gas. This phenomenon is called sublimation, and then a substance changes directly from gas to solid. This is called sublimation, sublimation absorbs heat and sublimation releases heat.

When the state of matter changes, the object needs to absorb heat or release heat. When an object changes from high density to low density, it absorbs heat; When it changes from low density to high density, it is exothermic.

The condition of heat absorption or heat release is heat transfer, so there is no temperature difference between the object and the surrounding environment, so there will be no state change. Such as 0 degrees Celsius.

2. Know little about science

Why does sorbet get angry? The reason why sorbet bubbles is because there is a lot of invisible water vapor in the outside air. When it comes to cold sorbet, it will liquefy into droplets when it is cold. It seems that the sorbet is bubbling.

Why do sunflowers always face the sun? Sunflower stems contain a wonderful auxin. This auxin is very afraid of light.

When it is illuminated, it will go to the backlight side, and the cells on the backlight side will multiply rapidly. Therefore, the backlit side will grow faster than the bright side, which will bend the sunflower to light. Why does cicada shed its skin? Cicada's shell (exoskeleton) is hard and can't expand with the growth of cicada. When the cicada grows to a certain stage, the cicada's exoskeleton restricts its growth, and the cicada loses its original exoskeleton, which is cicada slough.

How do bees make honey? First, the bees spit the sweet juice of the flowers they picked into an empty hive. At night, they suck sweet juice into their honey stomachs to make it, and then spit it out and swallow it. It takes 100~240 times to make sweet honey. How do birds sleep? During the day, birds shuttle in the branches, chirp and fly freely under the blue sky. At night, they should rest, sleep and recover their strength like us, but the sleeping posture is different! Beautiful mallard ducks and swans hunt and play in the water during the day, but they can't rest when they leave their favorite water at night.

They bend their beautiful long necks, bury their heads in their wings, and then let themselves float on the water, dreaming a beautiful dream, drifting with the tide, very leisurely. Long-legged birds such as cranes, storks and herons always sleep independently on one foot, and when they are tired, they change their other feet, which is a model of combining work and rest.

Partridges like to form a big circle in groups when resting, and then their heads are outward and their tails are inward. In this way, no matter which direction the enemy attacks, they can find and escape in time.

Birds with sweet voices, such as blackbirds and larks, usually bend their legs when sleeping, and their claws bend to firmly grasp the branches without worrying about falling from the trees. And the owl, a "night-shift" raptor, you can always see it standing on a dense branch with one eye open during the day, actually sleeping.

Isn't the owl's sleeping position very different? Is to monitor the surrounding environment at all times and guard against enemy attacks.

3. Why do pupils embroider their nails?

The nail is made of iron. After reacting with oxygen and water molecules in the air, iron will be oxidized into iron oxide, which is often called rust.

When iron combines with oxides dissolved in water, it will rust. This means that if there is no water vapor in the air, or no water at all, or no dissolved oxygen in the water, rust will not form.

When a drop of rain falls on the shiny iron surface, it will remain clean for a short time. However, before long, iron and oxygen in the water began to combine to form iron oxide, which is rust.

Water drops will turn red and rust will be suspended in water. When the water droplets evaporate, rust will remain on the surface, forming a reddish rust layer.

Once rust is formed, it will spread even in dry air. This is because rough rust is easy to condense water vapor in the air, and water vapor absorbs water vapor and stores it, which is why it is much easier to prevent iron from rusting than to prevent rust from expanding.

Rust is a fragile and porous substance, which can't protect the iron in the inner layer from corrosion, so over time, steel products may rust into a pile of useless waste products. It is particularly serious that steel will soon rust in water vapor containing acid gas and chlorine gas, or when it comes into contact with electrolyte solution.

According to statistics, tens of millions of tons of steel have become rust in every country in the world. The destruction of steel products has caused production suspension, product quality decline, environmental pollution and harm to people.

4. Less knowledge of popular science

The physical principle of rainbow is a natural light phenomenon that people often see.

Whenever colorful rainbows hang in the sky, people can't help rushing to this beautiful nature. In ancient times, some people said that it was the lonely Chang 'e singing and dancing colorful silk in the clouds; Some people say that it is a colorful bridge built by fairies in the clouds to peep at the world.

Whether it is colored silk or colored bridge, it is just a magical legend. And what is the rainbow in reality? How is it formed? When it comes to the formation of rainbows, people often think of it.

After rain. Be with each other.

Many people think that only. After rain.

There is a rainbow. Actually, this view is not comprehensive.

After rain.

It is true that rainbows sometimes appear in the sky, but rainbows also appear around fountains or waterfalls in the sun; In summer, sometimes there will be a rainbow behind the sprinkler running in the street; Spraying in the air with a sprayer can also form a rainbow. Obviously, that kind of rainbow only exists in.

After rain. The reason for the rainbow has not been fully understood.

As long as we know that it is conditional to see rainbows in the air, we naturally know that rainbows don't have to rain to appear. There is a teacher in the middle school physics class.

Scattering of light. Experiment: Take a prism and let a beam of white light pass through the slit and shine on one side of the prism. After passing through the prism, the advancing direction changes, and a colored light band is formed on the white screen. The order is red, orange, yellow, green, blue, indigo and purple.

This is very similar to the color of a rainbow. But it is impossible to have a prism in the air to form a rainbow.

Why is this? This is because there are a lot of small water droplets floating in the air. When the sun shines on these small water droplets, one by one, like a prism, decomposes the white light into seven monochromatic lights, which have dispersion effect on the sun.

How does sunlight produce spectral dispersion in small water droplets? Sunlight enters water droplets, that is, it enters water from the medium of air and undergoes a refraction. Due to the different refractive indexes of various monochromatic lights that make up white light, violet light has the shortest wavelength and the largest refractive index, red light has the longest refractive index and the smallest refractive index, and other colored lights are in between. Therefore, the light is split in the water drop, and the light of various colors continues to spread in the water drop at the same time, and is reflected back when it meets another interface of the water drop, passes through the inside of the water drop again, and refracts back into the air when it comes out.

In this way, the sunlight in the water drops undergoes twice refraction and once total reflection, and is decomposed into seven monochromatic lights: red, orange, yellow, green, blue, indigo and purple. When there are a large number of water droplets in the air, sunlight passes through these water droplets, and after reflection and refraction, the emitted light gathers together to form a beautiful rainbow in the sky.

Usually, most of what we see is a rainbow, and the viewing angle (from the ground to the top of the rainbow) is about 42. Sometimes you can see another rainbow with the opposite color order and deeper color outside the rainbow. This rainbow is called the second rainbow.

The main rainbow is internal ultraviolet red, the auxiliary rainbow is internal infrared purple, and the auxiliary rainbow is also called neon. Neon and main rainbow are concentric arcs, and the sky between them is dark, while the sky inside and outside the rainbow is bright.

The viewing angle of neon is about 5 1. Its origin is basically the same as the main rainbow.

It is formed by two reflections and two refractions of sunlight in small raindrops, namely refraction-total reflection-total reflection-refraction. On the ground level, the main rainbows and neon lights we see are semicircular because their lower parts are covered by the ground.

If you stand on the top of a high mountain, you can see most of the major rainbows and neon lights. Only when the weather is clear, looking down in the aircraft cabin, can we see the whole picture of the main rainbow and neon, that is, a complete circle.

If the angle of the sun is too big (for example, around noon) or too small (the recently rising or setting sun), it is not easy for us to see rainbows, and because rainbows enter our eyes through the reflection of sunlight by small water droplets, rainbows always appear opposite the sun. The morning rainbow is in the west and the evening rainbow is in the east.

It appears mainly in summer.

Why is the main rainbow ultraviolet red? When we look at a rainbow, colored light is reflected from small water droplets at different angles. For a particle, only one color of light can enter our eyes, while other colors of light refracted from the same raindrop pass through our eyes high or low without being seen by us. Specifically, among the light that can enter our eyes and be refracted by water droplets at the highest position, red light can enter our eyes because it has the smallest refractive index and the smallest deflection angle. We only see red light, and other colors of light pass over our heads because of their large refractive index and large deflection angle.

A slightly lower water drop can only be seen by orange light with deflection angle greater than red light and less than other colors under refracted light. Among other colors, red light is low, yellow, green, blue, indigo and purple are high, which are beyond our eyes.

By analogy, the light that enters our eyes and is refracted by the lowest water drop can only see purple light, and the rest of the colored light slips away from our noses. In this way, the light refracted by adjacent water droplets in the air forms a rainbow, which is ultraviolet and red.

Meteorological principles of rainbows The size of water droplets in the air determines the color and width of rainbows. The bigger the raindrops, the narrower the rainbow band and the brighter the color. The smaller the raindrops, the wider the rainbow band and the darker the color.

When raindrops are small enough, the light splitting and reflection are not obvious, and the rainbow disappears. This shows that the formation of rainbow is directly related to the existence, quantity and size of raindrops in the air, and in turn, rainbow is related to weather changes.

For example, the color of the rainbow changes from bright to dark, and the width changes from narrow to wide, indicating that the raindrops in the air change from big to small. It can be speculated that the air may gradually stabilize and the weather conditions will gradually stabilize.