100 life or production phenomena and corresponding physics knowledge in junior high school

Analysis of common physical phenomenaPhenomenon 1: The magic of "9".

Quartz clocks hanging on the wall often stop at the "9" position on the dial when the battery runs out of power and stops moving. Isn't it weird?

Decryption

This is due to the fact that the second hand is most hindered by the gravitational moment at this position where the "9" is located.

When the temperature of an object rises, it "doesn't necessarily" absorbs heat

[Brief Analysis].

When the temperature of the object increases, it can only mean that the irregular thermal motion of the molecules inside the object accelerates, and the internal energy of the object increases. There are two ways to increase the energy inside an object: to allow the object to absorb heat (heat transfer) and to do work on the object from the outside world (work).

For example, if the temperature of a saw blade rises, it may absorb heat by roasting it in the oven; It may also be that the wood has just been sawed, that is, by overcoming the friction to do work, its own internal energy increases, and the temperature rises.

[Conclusion].

Both heat transfer and work can change the internal energy of an object, and heat transfer and work done are equivalent in changing the internal energy of an object.

Optical aspects

1. Fishing for the moon in the water is empty (what you can't pick is the moon in the mirror, and what you can't catch is the flower in the water): Because the calm water surface is equivalent to a flat mirror, and the image made by the plane mirror is like a virtual image, so of course it is in vain.

2. Zhu Bajie looks in the mirror - not a person inside and outside: according to the law of plane mirror imaging, the object and the image are symmetrical, the image is exactly the same as the object, and the pig is of course not a person inside and out.

3. Mirage: When the sunlight that hits the ground in the distance is reflected into the air, it is refracted due to the uneven density of the air, and what you see is a virtual image formed by the distant scenery.

4. One day in the cave, thousands of years in the world: According to Einstein's theory of relativity, traveling in the universe close to the speed of light, the passage of time will be much slower than on the earth, and living in this "hole" for a day, the earth has spent years, decades, or even thousands of years.

5. Sitting in a well and watching the sky, you see very little: this is the reason why light travels in a straight line in the same substance.

What is the content of junior high school physics pendulum, uniform linear motion, light (light, reflection, oblique radiation, convex lens imaging), sound (echo, loudness, tone, timbre, noise), force (gravity support force, etc., two-force balance, friction, inertia, lever, pulley, pressure, pressure, power), heat (specific heat), electricity (draw circuit diagram, series, parallel, current, voltage, electric power).

The above is what are the common physical phenomena in junior high school that I have compiled for you.

1. Keep ventilation when drying clothes and accelerate evaporation;

2. Blowing soap bubbles colorful, refracting light;

3. The lake reflects the beautiful white sails, the reflection of light;

4. There is white smoke around the ice cream in summer, which is liquefied;

5. Hot soup can not be drunk with water, and the boiling point is different;

6. The fried food water has high impact content and low content, and the density is different;

7. When the hydrogen balloon flies into the sky, the buoyancy is greater than the gravity;

8. Put two kicks and the earth vibrates, and the sound is propagated by waves;

9. In summer, the tube sweats and liquefies;

10. The wire is made of copper core, and copper is a good conductor of electricity second only to silver;

11.The needle tube can be pierced, but the wooden stick is difficult, and the pressure is different;

12.The bicycle belt is changed well to increase the friction;

13.Wind power generation, the conversion of mechanical energy into electrical energy;

14.The maglev train runs at high speed, with low friction;

15.Seesaw, lever principle.

19.Skating, reducing the contact area and reducing friction.

If the lights go out suddenly, we always have to check whether the fuse has blown out, and most of the problems do come from here. If the fuse is broken, just turn off the main electric door, replace it with a new fuse, and then close the main electric gate switch, and the electric light will immediately turn on again. Why is it that wiring in other places is not easy to blow out, but fuses are easy to blow out?

It turns out that although the fuse is also a metal wire, it is different from ordinary copper wire and iron wire.

It is soft and made of lead, antimony, or low melting point alloys such as lead and tin. It has a relatively large resistivity, a relatively low melting point, and is naturally afraid of heat. Due to the thermal effect of the current, as long as the current passing through the fuse exceeds the rated current of the fuse and reaches the blowing current, the fuse will blow quickly, automatically disconnecting the circuit from the power supply.

In this way, the strong current can no longer enter the user's home, thus preventing the meters, appliances or wires connected to the circuit from burning out due to excessive current.

For example, in everyday life, you will see mufflers for motorcycles. The physics used here is to attenuate the noise from the sound source.

Acoustic panels next to urban roads, which are used to control noise during propagation.

Workers in the factory wear noise-proof earmuffs, which are out of the human ear.

1. Apply the difference in the refractive index of light in different media to explain that chopsticks look like they are broken when immersed in water!

2. The difference in the propagation speed of light and sound explains why lightning is seen first and then thunder is heard.