It's time for science! 10 scientific knowledge that is worth explaining to your children, come and see

1. Isn't it much clearer to teach children to study Pythagorean theorem in this way!

Do you still remember how your teacher proved it to you when you were studying the Pythagorean theorem? Draw a picture to draw it, or measure it straight with a ruler and calculate? I'm afraid there is nothing more intuitive than this device.

2. Why do sunflowers always face sun?

Sunflower stems contain auxin, which is afraid of light. When exposed to light, it moves to side of light, and also stimulates rapid reproduction of cells on side of light. This is why people have discovered that sunflowers always follow sun. In fact, this phenomenon only exists from emergence to flowering of sunflower plants, whose leaves and flower discs will change from east to west as sun rotates each day. After flowers bloom, it will no longer turn, but will be directed to east.

3. Why is there a whistling sound when wind blows?

The whistling sound we hear is actually sound made by a strong wind when it hits a wire or a thin object such as a branch. The same is true for wind blowing on tree branches. A strong wind forms a vortex at an acute angle, which makes a "whistling" sound. The stronger wind, louder sound.

4. Why do trees shed their leaves in autumn?

Defoliation of trees is a self-defense method, which consists in correcting balance in body and reducing loss of water and nutrients. Leaves begin to fall in autumn to store energy and wait for spring to sprout again. And some trees, such as pines and cypresses, can remain evergreen and never lose their leaves because their leaves are needle-like and use very little water and nutrients.

5. Why do most fallen leaves face up?

This is a very interesting phenomenon. Most fallen plant leaves look up and down. Why?This is due to special structure inside leaves. For leaves of most plants, there is a significant difference in sunlight received by back and front during plant growth, resulting in differences in structure of two sides of leaf. Typically, cells near surface of leaf are rectangular and arranged regularly, called palisade tissue, while cells near back of leaf are arranged in irregular blocks, called spongy tissue. The density of palisade fabric is denser, so weight of leaf is greater, and when leaf falls, heavier side faces down and back of leaf faces up.

6. Why does water splatter when it hits hot oil?

During cooking, as soon as water enters pan with hot oil, it splashes. This is a very common phenomenon in life, but how many have thought about reason for this?

Correct answer: Normally hot oil temperature is 160°C~200°C, and water boiling point is 100°C. The boiling of a liquid is evaporation. The temperature of hot oil is much higher than boiling point of water. At this time, when water enters oil pan, it evaporates and vaporizes with an explosion. Thus, surrounding oil is splashed, forming "oil spatter" phenomenon.

7. Why does milk separate after heating?

Many people are used to drinking hot milk. After heating, they will find a thin layer of skin on surface of milk. Why?

Correct answer: In fact, it is a protein after coagulation. When protein is heated, it coagulates like a boiled egg. Once heated, protein in egg coagulates.

8. Why do some people feel like sleeping when they are full?

Are there people around you who are very energetic after dinner but seem sleepy after a while, why?

Correct answer: due to parasympathetic hyperactivity. Food stimulation will make our parasympathetic nerves relatively energized, and energized parasympathetic nerves will help us improve digestion, absorb nutrients, and replenish energy, but at same time, it will also cause our blood pressure, heart rate, body temperature, and breathing to drop, such thus entering a state where it is easy to fall asleep.

9. Why is shell of boiled eggs easy to peel after soaking in cold water?

Many people know this common sense: soak freshly boiled eggs in cold water, and eggshell will be easily peeled. Why is that?

Correct answer: Eggs are made up of three parts: shell, white and yolk. Between eggshell and egg white is a thin layer of eggshell shell, which is protein gelatin, this film is difficult to remove without soaking in cold water.

Eggshells look airtight, but are actually a bit breathable. Inside egg there are air chambers (air bubbles). The fresher egg, smaller air chamber, and longer egg is stored, air chamber gradually becomes larger. When an egg is boiled, air in air chamber expands and some of air escapes from shell. When immersing an egg in water immediately after cooking, a small amount of water will enter egg shell due to depressurization in air chamber, and film on egg shell will peel off more easily when in contact with water.

10. Why do you see lightning first and then hear thunder?

The correct answer is: because light waves travel faster than sound in air.

During thunderstorms and rain, we often see lightning first and hear thunder a few seconds later. But if you mistakenly think that first lightning and then thunder, then you are mistaken. In fact, both things happen at same time, simply because in air speed of light is about 300,000 km / s, and speed of propagation is speed of sound in air The speed is much slower, about 0.34 km/s, and speed of light is about 880,000 times speed of sound, which is why we first see lightning and then hear thunder.