Review of scientific knowledge points under the fifth edition of People's Education Press

Review of scientific knowledge points under the fifth edition of People's Education Press

Unit 3 Measurement of Time

1. Time is passing: We can estimate the time through regular or rhythmic activities, such as heartbeat, tapping on the table rhythmically, etc. But according to our estimation, we can't know when it will be ready. You can write () a few words a minute, read () lines, run () meters and so on. Time is passing at a constant speed, and it is our feeling that time is fast or slow at ordinary times.

Sun clock: Before the invention of clocks and watches, people measured time according to the position of the sun in the sky, making it work at sunrise and rest at sunset. In ancient times, we divided a day (day and night) into twelve hours, and now each hour is two hours. According to the crossing of 36 constellations in the sky in a year, ancient Egypt divided a day into 24 hours, with 12 in the daytime and 12 in the evening. Because the length of day and night changes with the seasons, the length of each hour in ancient Egypt also changes. The sundial uses the change of the position of the sun in the sky to change the shadow length and position of objects on the ground to time.

Third, water timing: there are two kinds of ancient water clocks: the water receiving type is based on the increase of water quantity, and the scale is generally on the lower container, and the water discharging type is based on the decrease of water quantity, and the scale is generally on the upper container. In the dripping experiment, if the water flows downwards, the velocity of the water is not fixed and will slow down with the decrease of the water quantity. The less water in the container, the slower the water flows.

My water clock: two plastic bottles are combined into a simple water clock. The general steps of design and manufacture are as follows: 1. 1. Select the type of water bell (water receiving type or water discharging type); 2. Determine the total water quantity; 3. Keep the water velocity constant. Water receiving type (make the water drop or keep the total water quantity unchanged. Discharge type (making water drop) Fourth, measure the amount of water in one minute. 5. Guess the remaining ten minutes of water.

5. Mechanical pendulum clock: The pendulum of pendulum clock swings 60 times per minute, and the number of times in the first minute is the same. A string with a fixed upper end and a small weight hanging from the lower end forms a simple pendulum. In the process of swinging, the direction and speed remain unchanged, and the amplitude is getting smaller and smaller.

6. Research on Pendulum: Different pendulums swing freely at different speeds. We study the weight, pulling range and length of pendulum rope, and find that the speed of pendulum is related to the length of pendulum. The longer the pendulum is, the slower it will be.

7. Make a pendulum: the length of the pendulum changes without changing the length of the pendulum rope. It is found that the longer the pendulum, the slower the speed. It is concluded that the speed of pendulum is related to the length of pendulum (the length of pendulum rope plus pendulum). The longer the swing, the slower the speed. Hanging a weight at the bottom of the pendulum, it is found that the pendulum with weight is slower than the pendulum without weight. When comparing pendulum with weight, it is found that the speed of pendulum is related to the position of weight. The lower the weight, the slower it swings, and the higher it is, the faster it swings. To adjust the swinging speed of the pendulum, we only need to adjust the position of the weight. From slow to fast, the weight goes up, from fast to slow, the weight goes down.

8. Make a one-minute timer: the timer consists of a gear controller, a support shaft, a long needle and a short needle, a pendulum, a gear and a pituitary gland. The gear controller is controlled by the pendulum, and the gear is controlled by the pituitary gland. Design a minute timer, which can be made into a water clock, a pendulum clock and so on.

Unit 4 The Movement of the Earth

1. Day and night alternation phenomenon: Seeing the day and night alternation on the earth, we can put forward the following assumptions: 1. The earth does not move, and the sun revolves around it. 2. The sun does not move, and the earth moves around the sun. The sun does not move, but the earth rotates. The earth revolves around the sun and rotates at the same time. To judge which hypothesis is correct, we must first determine an area on the earth as a tool for the sun and the earth, and then carry out experiments. After the experiment, it is found that these four hypotheses can make a certain area of the earth alternate day and night. It is impossible to determine which hypothesis is correct just by alternating day and night, so we must look for new and more evidence.

Second, human understanding of the earth's history and movement: views and theories, geocentric theory: ancient Greek astronomer Ptolemy proposed that the earth is a sphere, the earth stands still in the center of the universe, and the sun revolves around the earth. Heliocentrism: The Polish astronomer Copernicus wrote On the Movement of Celestial Bodies. The earth is spherical and moving, rotates once every 24 hours, is stationary on the sun, and the earth revolves around the sun.

Third, prove that the earth is rotating: put the pendulum and its bracket on a circular chassis, and rotate the chassis when the pendulum swings. The swinging direction of the pendulum does not change with the rotation of the chassis, but basically remains unchanged. 300 years after Heliocentrism's publication, Foucault used Foucault pendulum to prove that the earth was rotating. He found that with the passage of time, the direction of the dial on the ground would deviate from the direction of the pendulum. Because the direction of the pendulum can remain the same, it can only show that the earth is turning on its own. Foucault pendulum, as evidence of the earth's rotation, has been recognized by the world.

4. Who greets the dawn first: The earth is spinning, and the direction of rotation is different, and the time and order of greeting the dawn are different in different places. When we sit in the moving train and look at the motionless trees outside, the trees move in the opposite direction to ours. We are on the moving earth. When we see the sun moving from east to west (clockwise), the direction of our original rotating earth is just opposite to that of the sun, from west to east (counterclockwise). We can judge the time by the world time zone map. The world time zone map divides the earth into 24 time zones based on the meridian of the earth. The meridian that passes through the Greenfield Observatory in London, England, is designated as the 0-degree meridian. The longitude of 0 degrees is 180 degrees east longitude and 180 degrees west longitude. Every 15 degrees is a time zone, and the difference between two adjacent time zones is 1 hour. The farther east (right) the city is on the map, the sooner you can see the sun. When you know that cities in the east are counted as cities in the west, you should subtract the time difference, and when you know that cities in the west are counted as cities in the east, you should add the time difference. Beijing is in the East Eighth District and new york is in the West Fifth District, with a difference of 13 hours. It's daytime in Beijing and night in new york.

5. The secret of the immobility of Polaris: The earth rotates around the earth axis, because Polaris is motionless in the sky at night, and it is on the north extension line of the earth axis. The earth's axis is tilted, because the Polaris we see is in the northern sky rather than in the middle of the head. The tilt direction of the earth's axis is constant all the year round, because the Polaris we see in the sky is motionless and its position has not changed, and the earth's axis always points to the Polaris.

6. Is the earth spinning? The evidence of the earth's revolution is as follows: 1. When people observe the constellations in the sky at the same time on different nights, they find that the positions of constellations in the sky will move from east to west with the passage of time, such as the Big Dipper. Second, the relative position difference of vision-the annual parallax of stars-can also prove that the earth is rotating when people observe stars at different distances. When we watch two stars with different distances on the earth, the relative distance and position between the two stars have changed in different seasons.

Seven, why there are four seasons in a year: at noon in different seasons of spring, summer, autumn and winter, the ancients found that the shadow length of the pole on the ground in the same place was different. The shadow in spring and autumn is moderate, the shortest in summer and the longest in winter, which is related to the height of the sun in the sky. Direct and oblique sunlight causes temperature differences in different parts of the earth. In spring and autumn, the sun shines directly in the equatorial region, which is the hottest. The sun shines obliquely in the northern and southern hemispheres, and the temperature is suitable in spring and autumn. In summer in the northern hemisphere, the direct point of sunlight is in the northern hemisphere, while in the southern hemisphere, the sunlight is weak, so the summer in the northern hemisphere is the winter in the southern hemisphere. The sun in the northern hemisphere shines directly in the southern hemisphere in winter. The sunshine in the northern hemisphere is oblique and weak, so it is summer in the southern hemisphere, and the seasons in the northern and southern hemispheres are just the opposite. The four seasons are formed because the position of the point where the sun shines directly on the earth has changed.

Explanation of the extreme phenomenon of day and night: In the north and south poles of the earth, half a year is day, half a year is night, and the north and south poles are just the opposite. The main reason is that the earth is tilted, and solar energy illuminates half the earth. When the earth revolves, the end inclined to the sun is always illuminated by the sun when the earth rotates. Movement of the earth: rotation: from west to east, counterclockwise, around the earth's axis and tilted to the north, with a period of about 24 hours, which is proved by Foucault pendulum, leading to alternation of day and night and immobility of Polaris. Mass communication: rotating counterclockwise around the sun from west to east, with a period of one year, which is proved by the disparity of sidereal years in different seasons and the movement of constellations in the sky at the same time. There are four seasons and extreme phenomena of day and night in the north and south poles. There are some interesting phenomena in the process of understanding the earth's movement, such as short sunshine in winter and long sunshine in summer, and the orbit of the earth's revolution is elliptical.