Physical principles: reflection and refraction of light.
The mountains are stacked in the water, and there is a reflection of the mountains in the water. There is no unattractive mountain, no unattractive water.
Second, Hanshan Temple outside Gusu City, the midnight bell goes to the passenger ship. -Zhang Tang Ji "Sleeping in Fengjiang"
The spread of sound.
In the lonely and quiet Hanshan Temple outside Gusu, the bell rang to the passenger ship in the middle of the night.
Third, the green hills on both sides of the strait are opposite, and the sails are coming alone. -Tang Li Bai's "Looking at Tianmen Mountain"
Physical principle: Castle Peak is static relative to the ground, but with the moving ship as the reference, Castle Peak becomes moving, with the river bank as the reference, and the solitary sail comes from the sun.
The beautiful scenery of the green hills on both sides of the strait is inseparable, and a solitary boat comes from the horizon.
April, April, beautiful scenery on earth, peach blossoms in mountain temples. -Tang Bai Juyi's Peach Blossom in Dalin Temple
Physical principle: The higher the terrain, the slower the temperature rises. In the same season, the temperature on the mountain is lower than that on the mountain.
In April, all the flowers have withered, and the peach blossoms in the ancient temple in the mountains have just bloomed.
Verb (abbreviation of verb) How the water of the Yellow River flows out of heaven and into the ocean, which is gone forever. -Tang Li Bai's "Into the Wine"
Physical principle: water cycle.
The water of the Yellow River fell from the sky, and the waves rolled straight into the East China Sea, never to return.
2. Poetry about physics 1. Mountain peaks float, no water, no mountains and no ecstasy.
-Physical principle of modern Wu Mai's Guilin Landscape: reflection and refraction of light. The mountains are stacked in the water, and there is a reflection of the mountains in the water. There is no unattractive mountain, no unattractive water.
Second, Hanshan Temple outside Gusu City, the midnight bell goes to the passenger ship. -Tang Zhangji's "Sleeping by the Fengjiang River" Physical principle: the spread of sound.
In the lonely and quiet Hanshan Temple outside Gusu, the bell rang to the passenger ship in the middle of the night. Third, the green hills on both sides of the strait are opposite, and the sails are coming alone.
-Tang Li Bai's "Looking at Tianmen Mountain" Physical principle: Compared with the green hills on the ground, it is static, but with the moving ship as the reference, the green hills become moving. Taking the river bank as a reference, the solitary sail comes from the sun. The beautiful scenery of the green hills on both sides of the strait is inseparable, and a solitary boat comes from the horizon.
April, April, beautiful scenery on earth, peach blossoms in mountain temples. -Tang Juyi's "Peach Blossom in Dalin Temple" Physical principle: The higher the terrain, the slower the temperature rises. In the same season, the temperature in the mountains is lower than that in the mountains.
In April, all the flowers have withered, and the peach blossoms in the ancient temple in the mountains have just bloomed. 5. How does the water of the Yellow River flow out of heaven and into the ocean, which is gone forever?
-Tang Li Bai's "Into the Wine" physical principle: water cycle. The water of the Yellow River fell from the sky, and the waves rolled straight into the East China Sea, never to return.
3. Physics of gravity 1. The concept of gravity
1, content: The force exerted by the gravity of the earth on an object is called gravity. An object is subjected to the gravity of 10N, or its weight is 10N.
2. Understanding: Gravity is the force that an object receives due to the gravity of the earth, not the gravity of the earth. Through the study of the chapter of gravity, we will know that gravity is a component of gravity, and the other component provides the centripetal force of an object rotating with the earth.
Second, the conditions of gravity.
Content: On or near the ground.
2. Understanding: From the concept of universal gravitation, it can be known that being attracted to the earth is of course on or near the earth. Broadly speaking, when an object is attracted to the moon on the moon, it will also be subjected to "gravity" (this gravity has nothing to do with the earth). The gravity of the spacecraft moving from the earth to the moon should be the resultant force of the earth's gravity and the moon's gravity, so when it moves to a certain position, the resultant force is zero, that is, the "gravity acceleration" is zero; Near the ground, the gravity of the earth is much greater than that of the moon, so it is considered that the gravity of the moon is equal to that of the earth. When near the moon, the attraction of the moon to objects is much greater than that of the earth, and it is considered that gravity is equal to the attraction of the moon.
Three elements of gravity
1, the magnitude of gravity:
(1) formula G=mg, where g=9.8N/kg=9.8m/s2 gravity acceleration.
(2) Measurement: spring scale (when using, hook a heavy object with a hand-held ring and keep it vertically still or move at a constant speed).
③ unit Newton unit symbol n
(4) Conclusion: The gravity of an object resting on a horizontal desktop is equal to the pressure of the object on the desktop. Note that there are two preconditions for this conclusion: "the desktop is horizontal" and "whether the object is stationary or moving at a constant speed" are both indispensable. For example, "does the gravity of an object on a horizontal desktop necessarily equal the pressure of the object on the desktop?" This sentence is wrong because it lacks the premise of "static or uniform motion"
2. Gravity direction: vertical downward. Can't say it's vertically downward.
3. Center of gravity-center of gravity
(1) Concept: The concentrated point where gravity acts on all parts of an object is called the center of gravity. After studying the composition of forces, the center of gravity can be expressed as the point where all parts of the object are subjected to the resultant force of gravity. The center of gravity is not the heaviest point on the object.
(2) center of gravity position:
A the position of the center of gravity depends on the mass distribution and shape of the object. For objects with uniform mass distribution (uniform objects), the center of gravity is only determined by the shape; A uniform object with regular shape, the center of gravity of which is on the geometric center of gravity.
* It should be noted that the premise of "geometric center of gravity" in the conclusion is that "uniform distribution of mass" and "shape rule" are indispensable. For example: a metal ball is half aluminum and half platinum, so the center of gravity of the object must be on the platinum side instead of the center of the ball; Does that contradict the conclusion of geometric center of gravity? Not contradictory. Because this object does not meet the prerequisite of "uniform distribution of mass"
* Calculation of the position change of the center of gravity of homogeneous objects: For example, a homogeneous metal bar with a length of L was originally placed on the horizontal ground, and now it stands vertically. How much has the center of gravity improved? If he bends into a circle, how much higher is his center of gravity when he stands upright than when he lies on a level ground?
B. the center of gravity may not be on the object.
C. measuring the center of gravity of an object by suspension method (the principle is two-force balance, and the applicable condition is thin plate)
(3) The significance of the center of gravity is that the position of the center of gravity is related to the stability of the object. The higher the center of gravity, the smaller the contact area and the more unstable the object is. When the contact area of an object is constant, the lower the center of gravity, the more stable the object is. For example, the chassis of a high-class car is very low, objects are hung on both sides instead of directly above the bicycle, people walking on a tightrope hold iron bars, and lunges and lunges in boxing are all aimed at lowering the center of gravity and increasing stability;
Fourth, the characteristics of gravity.
1, invariance
No matter the position, motion (static, uniform, accelerating) and whether it is acted by other forces, gravity remains unchanged.
For example, the following statement about gravity is incorrect:
A, only static objects have gravity;
B, when an object is in free fall, gravity disappears;
C, when the object has vertical acceleration, gravity is greater than when the object is at rest.
2. Gravity changes with the change of geographical location. It decreases with the elevation and increases with the latitude.
For example, a group of journalists flew from Shanghai to Tibet. Compared with their luggage in Shanghai, their luggage quality will be (fill in "bigger", "unchanged" and "smaller"); The magnitude of gravity will be (fill in "bigger", "unchanged" and "smaller").
Analysis: the mass of an object (luggage) refers to the quantity of substances contained in the object, which has nothing to do with geographical location and height. The gravity of an object is related to its geographical position and height. Shanghai and Tibet are basically at the same latitude, but Tibet is higher than Shanghai. The higher the height, the less gravity. So, the answer is. Same, smaller.