Fourth grade knowledge sharing

Fourth grade knowledge 1. Fourth grade knowledge of mathematics

The knowledge points of mathematics in the fourth grade of primary school are summarized in the first volume of the fourth grade. The knowledge points are summarized in 1. Understanding of large numbers: understanding of numbers within (1) billion:100000:10/0000; One million:100000; Ten million:100000; 1 100 million:1010 million; 2. Digital scale: Digital scale is a reading method for people to remember and read * * * numbers. On the basis of numerical system (numerical order), read and write numbers according to the principle of three-digit or four-digit grading.

Usually, in the writing of * * * numbers, decimal points or spaces are used as the marks of each number level, and the numbers are separated from right to left. 3. Grade classification (1) The four-digit classification method is a classification method with four digits as a grade.

The habit of reading in our country is like this. Such as: ten thousand (four zeros after counting), one hundred million (eight zeros after counting), and one trillion (12 zeros after counting, which is a normal number).

These levels are called Level 1, Level 10,000 and Level 100 million respectively. (2) Three-digit classification is a classification with three digits as an order of magnitude.

This western classification, this classification is also an internationally accepted classification. For example, thousands, followed by three zeros and millions, six zeros and one billion, and nine zeros.

4. Numbers: Numbers refer to writing numbers in a row side by side, and each number occupies a position. These positions are called numbers. Starting from the right end, the first place is the unit, the second place is the tenth place, the third place is the hundred places, the fourth place is the thousand places, and the fifth place is the ten thousand places, and so on.

This shows that the concept of counting unit and number is different. 5. Generation of Numbers: Origin of * * * Numbers: After ancient Indians created * * * numbers, they spread to * * * regions around the 7th century.

By the 3rd century A.D./KLOC-0, the Italian mathematician Fibonacci wrote Abacus, in which he introduced the number of * * * in detail. Later, these figures spread from * * * to Europe. Europeans only know that these numbers are imported from * * * regions, so they are called * * * numbers.

Later, these figures spread from Europe to all countries in the world. * * * Numbers were introduced into China from about 13 to 14 century.

Because there was a number called "Chip" in ancient China, which was convenient for writing, the number * * * was not popularized and used in time in China at that time. At the beginning of this century, with the absorption and introduction of foreign mathematical achievements in China, the number * * * began to be used slowly in China, and it has only been popularized and used in China for more than 100 years.

* * * Numbers have now become the most commonly used numbers in people's study, life and communication. 6. Natural number: a number used to measure the number of things or to indicate the order of things.

That is, the numbers represented by the numbers 0, 1, 2, 3, 4, and ... the numbers representing the number of objects are called natural numbers, and they form an infinite group one by one from 0 (inclusive).

7. Computing tools: abacus, calculator and computer. 8. Ray: In geometry, the figure formed by a point on a straight line and its edge is called a ray.

As shown in the following figure: 8. Ray characteristics (1) A ray has only one endpoint, and it extends from one endpoint to the other indefinitely. (2) Ray is unpredictable.

9. Straight line: A straight line is the trajectory of a point moving in the same or opposite direction in space. 10. Line segment: A line segment is represented by letters or lowercase letters representing its two endpoints. Sometimes these letters also represent the length of the line segment, which is recorded as line segment AB or line segment BA and line segment A. ..

Where AB represents any two points on a straight line. 1 1. The line segment feature (1) has a finite length and can measure (2) two endpoints 12. Line segment attribute: (1) The line segment between two points is the shortest.

(2) The length of the line segment connecting two points is called the distance between these two points. (3) Two points on a straight line and the part between them are called line segments, and these two points are called the endpoints of the line segments.

There is no distance in a straight line. Ray has no distance.

Because a straight line has no end point, and a ray has only one end point, it can extend indefinitely. 13. The static definition of an angle (1) is called an angle.

This common endpoint is called the vertex of the angle, and these two rays are called the two sides of the angle. (2) Dynamic definition of angle The graph formed by the rotation of light from one position to another around its endpoint is called angle.

The endpoint of the rotated ray is called the vertex of the angle, the ray at the starting position is called the starting edge of the angle, and the ray at the ending position is called the ending edge of the angle 14. Symbol of angle: ∠ 15. Type of angle: the size of the angle has nothing to do with the length of the side; The size of an angle depends on the degree to which both sides of the angle are open. The bigger the opening, the bigger the angle. Conversely, the smaller the opening, the smaller the angle. In dynamic definition, it depends on the direction and angle of rotation.

Angles can be divided into acute angle, right angle, obtuse angle, right angle, rounded corner, negative angle, positive angle, upper angle, lower angle and 0 angle, which are 10 respectively. An angle measuring system in degrees, minutes and seconds is called an angle system.

In addition, there are secret system, arc system and so on. (1) acute angle: an angle greater than 0 and less than 90 is called an acute angle.

(2) Right angle: An angle equal to 90 is called a right angle. (3) Oblique angle: An angle greater than 90 and less than180 is called obtuse angle.

16. multiplication: multiplication refers to how many times a number or quantity has increased. For example, 4 times 5, that is, 4 increases 5 times, or it can be said that 5 4' s are added together.

17. Names of numbers in the multiplication formula: "*" is a multiplication sign, numbers before and after the multiplication sign are called factors, "=" is an equal sign, and numbers after the equal sign are called products. 10 (factor) * (multiplication sign) 200 (factor) = (equal sign) 2000 (product) 18. Parallelism: Two straight lines on a plane, two planes in space or a straight line in space are said to be parallel when there is no common point between them.

As shown in the figure, the straight line AB is parallel to the straight line CD and marked as AB∑CD. Parallel lines will never intersect.

19. Vertical: two straight lines, two planes intersect, or a straight line intersects a plane. If the intersecting angles are right angles, they are called perpendicular to each other. 20. Parallelogram: A parallelogram with two groups of opposite sides on the same plane is called a parallelogram.

2 1. Trapezoid: Trapezoid refers to a set of quadrilaterals whose opposite sides are parallel and the other set of opposite sides are not parallel. Two parallel sides are called the bottom of the trapezoid, in which the long side is called the bottom and the short side is called the bottom; You can also simply think that the upper part is called the upper bottom and the lower part is called the lower bottom.

Non-parallel edges are called waist; The vertical section sandwiched between the two base sides is called the height of the trapezoid. 22. Division: Division rule: How many digits is the divisor, first.

2. The main categories of the fourth grade of primary school

Math section: 1. Make students master the characteristics of trapezoid and the names of each part, and communicate the connection between trapezoid and other plane graphics. 2. Further cultivate students' spatial imagination and hands-on operation ability. Let students understand the relationship between mathematics and life and cultivate their love for mathematics. Understand that divisor is the arithmetic of oral division of integer hundred, and master oral calculation methods. 3. Infiltrate mathematical knowledge from real life thoughts to cultivate students' initial innovative consciousness. Teaching emphasis.

Simply put, graphic knowledge is a trapezoidal part, and arithmetic knowledge is a familiar face to master the division language part 1. Master 2500 common words, of which 2000 can write. 2. Be able to use a dictionary and be fluent in Mandarin. 3. Learn how to master the central idea of the article. 4. Recite 10 ancient poems (articles). 5. Contact the English section 1. Able to understand and recognize. 2. Can listen, speak and read 75 words, can listen, speak, read and write 60 words, and can be used simply; 3. You can listen to and play the 14 game; 4. Can listen, do and perform. 5. Can sing; 6. Can understand humorous stories; 7. Understand simple knowledge of Chinese and Western cultures. It may be different from place to place, but as far as the four-level mind is concerned, this is basically the content.

3. What are the main points of mathematics knowledge in the fourth grade of primary school?

First, know the number within 1 100 million.

1 .1, 10, 100, 100, 100, 100 ... Billions are all units of counting.

2. What is the relationship between every two adjacent counting units?

The propulsion rate of every two adjacent counting units is "10".

3. The method of finding the divisor is called "rounding".

4. Whether to "give up" or "enter" depends on whether the highest digit of the omitted mantissa part is less than 5 or greater than 5.

5. Numbers 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,1,... are all natural numbers. The object is not represented by 0. 0 is also a natural number.

6. The smallest natural number is 0. There is no maximum natural number, and the number of natural numbers is infinite.

7. The forward speed between every two adjacent counting units is 10. This counting method is called decimal counting method.

Second, the angle measurement

1. The light emitted by flashlights, car lights and the sun can be approximately considered as light. A ray has only one endpoint and can extend to one end indefinitely.

2. A straight line has no endpoints and can extend to both ends indefinitely.

3. What is the connection and difference between straight line, shot money and line segment?

Connection: both ray and line segment are part of a straight line, and line segment is a limited part of a straight line.

Difference: A straight line has no end, unlimited length and extends in two directions; A ray has only one endpoint, and its length is infinite, extending in one direction; A line segment has two endpoints, and its length is limited.

4. Both straight lines and rays can extend indefinitely. Line segments can measure the length.

A figure consisting of two straight lines drawn from a point is called an angle.

6. The measurement unit of angle is "degree", which is expressed by the symbol "degree". Divide the semicircle into 180 equal parts, and the angle of each part is 1 degree, and record it as 1 degree.

7. What is the relationship between acute angle, obtuse angle, right angle, right angle and rounded corner?

Right angle =90 degrees, obtuse angle greater than right angle less than right angle, right angle = 180 degrees, fillet =360 degrees, acute angle less than 90 degrees, acute angle 8. The inclination angle is greater than 90 degrees, but less than 180 degrees. The acute angle is less than 90 degrees. A right angle is equal to 180, which is equal to two right angles.

Three, three digits multiplied by two digits

1. speed x time = distance

Four, parallelogram and trapezoid

1. Two straight lines that do not intersect in the same plane are called parallel lines, or they are parallel to each other. If two lines intersect at right angles, they are said to be perpendicular to each other, one of which is called the perpendicular of the other, and the intersection of these two lines is called the vertical foot.

2. The vertical line drawn from a point outside the straight line is the shortest, and its length is called the distance from that point to the straight line.

3. Two sets of quadrangles with parallel opposite sides are called parallelograms, and only one set of quadrangles with parallel opposite sides is called trapezoid.

4. Can rectangles and squares be regarded as special parallelograms? Why?

Yes, because the two opposite sides of a rectangle and a square are parallel and both are quadrilaterals, they can be regarded as special parallelograms.

5. Draw a vertical line from one point on one side of the parallelogram to the other. The line segment between this point and the vertical foot is called the height of the parallelogram, and the side where the vertical foot is located is called the bottom of the parallelogram.

6. An isosceles trapezoid is called an isosceles trapezoid.

7. There is a special parallelogram whose four sides are equal. This parallelogram is called a diamond.

5. Divider is the division of two digits.

Statistics of intransitive verbs

Seven, mathematics wide angle

4. Fourth-grade mathematics knowledge

Golden ratio

Divide a line segment into two parts so that the ratio of one part to the total length is equal to the ratio of the other part to this part. Its ratio is an irrational number, and the approximate value of the first three digits is 0.6 18. Because the shape designed according to this ratio is very beautiful, it is called golden section, also called Chinese-foreign ratio. This is a very interesting number. We use 0.6 18 to approximate it, and we can find it by simple calculation:

1/0.6 18= 1.6 18

( 1-0.6 18)/0.6 18=0.6 18

This value is not only reflected in the fields of painting, sculpture, music and architecture, but also plays an important role in management and engineering design.

Let's talk about a series. The first few digits are: 1, 1, 2, 3, 5, 8, 13, 2 1, 34, 55, 89, 144 ... The characteristic is that every number is the sum of the first two numbers except the first two numbers (the numerical value is 1).

What is the relationship between Fibonacci sequence and golden section? It is found that the ratio of two adjacent Fibonacci numbers gradually tends to the golden section ratio with the increase of the series. That is f (n)/f (n-1)-→ 0.618. Because Fibonacci numbers are all integers, and the quotient of the division of two integers is rational, it is just approaching the irrational number of the golden ratio. But when we continue to calculate the larger Fibonacci number, we will find that the ratio of two adjacent numbers is really very close to the golden ratio.

A telling example is the five-pointed star/regular pentagon. The pentagram is very beautiful. There are five stars on our national flag, and many countries also use five-pointed stars on their national flags. Why? Because the length relationship of all the line segments that can be found in the five-pointed star conforms to the golden section ratio. All triangles that appear after the diagonal of a regular pentagon is full are golden section triangles.

Because the vertex angle of the five-pointed star is 36 degrees, it can also be concluded that the golden section value is 2Sin 18.

The golden section is approximately equal to 0.6 18: 1.

Refers to the point where a line segment is divided into two parts, so that the ratio of the length of the original line segment to the longer part is the golden section. There are two such points on the line segment.

Using two golden points on the line segment, a regular pentagram and a regular pentagon can be made.

More than 2000 years ago, Odox Sass, the third largest mathematician of Athens School in ancient Greece, first proposed the golden section. The so-called golden section refers to dividing a line segment with length L into two parts, so that the ratio of one part to the whole is equal to the ratio of the other part. The simplest way to calculate the golden section is to calculate Fibonacci sequence 1, 1, 2,3,5,8,13,21. The ratio of the last two digits is 2/3, 3/5, 4/8, 8/ 13, 13/2 1. Probably.

Around the Renaissance, the golden section was introduced to Europe by * * * people and was welcomed by Europeans. They called it the "golden method", and a mathematician in Europe17th century even called it "the most valuable algorithm among all kinds of algorithms". This algorithm is called "three-rate method" or "three-number rule" in India, which is what we often say now.

In fact, the "golden section" is also recorded in China. Although it was not as early as ancient Greece, it was independently created by China ancient algebras and later introduced to India. After textual research. The European proportional algorithm originated in China and was introduced into Europe from India, not directly from ancient Greece.

Because it has aesthetic value in plastic arts, it can arouse people's aesthetic feeling in the design of length and width of arts and crafts and daily necessities, and it is also widely used in real life. The proportion of some line segments in the building adopts the golden section scientifically. The announcer on the stage is not standing in the center of the stage, but standing on the side of the stage. The position at the golden section of the stage length is the most beautiful and the sound transmission is the best. Even in the plant kingdom, the golden section is used. If you look down from the top of a twig, you will see that the leaves are arranged according to the golden section law. In many scientific experiments, a method of 0.6 18 is often used to select the scheme, that is, the optimization method, which enables us to arrange fewer experiments reasonably and find reasonable western and suitable technological conditions. It is precisely because of its extensive and important application in architecture, literature and art, industrial and agricultural production and scientific experiments that people call it the golden section.

The golden section is a mathematical proportional relationship. The golden section is strict in proportion, harmonious in art and rich in aesthetic value. Generally, it is 1.6 18 in application, just as pi is 3. 14 in application.

Discover history

Since the Pythagorean school in ancient Greece studied the drawing methods of regular pentagons and regular decagons in the 6th century BC, modern mathematicians have come to the conclusion that Pythagoras school had touched and even mastered the golden section at that time.

In the 4th century BC, eudoxus, an ancient Greek mathematician, first studied this problem systematically and established the theory of proportion.

When Euclid wrote The Elements of Geometry around 300 BC, he absorbed eudoxus's research results and further systematically discussed the golden section, which became the earliest treatise on the golden section.

5. Review the materials in the second volume of Grade Four.

People's education edition fourth grade Chinese review materials volume two, ancient poetry review. 1 Lesson Analysis of Ancient Poetry Collection The ancient poem "Sitting alone in Jingting Mountain" (Tang Libai) expresses the poet's loneliness caused by lack of talent.

Poetry: Birds are high, and lonely clouds go to leisure alone. You look at me, I look at you, and there are only my eyes and Jingting Mountain's eyes.

② Poetry: Many birds flew away, out of sight, and a white cloud drifted away leisurely and lonely. At this moment, only Jingtingshan and I look at each other, and we can't get enough of each other.

2. The ancient poem Looking at Dongting (Yuxi, Liu Tang) expresses the poet's love and praise for the beautiful scenery of Dongting. Poetry: the lake is full of moonlight, and there is no wind mirror on the pool surface.

Looking at Dongting from a distance, there is a green snail in the silver plate. Poetry: Autumn night, the moonlight is like water, and the water reflects the color of the moon. The two are in harmony.

The lake is calm and hazy, just like a polished bronze mirror. From a distance, the colors of Dongting Lake and Junshan Mountain are like green snails in a silver plate.

3. The poem "Remembering Jiangnan" (Tang Bai Juyi) expresses the poet's admiration and nostalgia for the beautiful scenery of Jiangnan. 1 verse: Jiangnan is good and the scenery is old.

When spring comes, the sun rises from the river, the flowers on the river are brighter than red, and the green river is greener than the blue grass. How can we make people not miss Jiangnan? Meaning: How beautiful the scenery in the south of the Yangtze River is, and the picturesque scenery has long been familiar.

The sun rises from the river, the flowers on the river are hotter than red, and spring is coming. The green river is like blue grass. How can one not miss Jiangnan? 4. Collection of Famous Poems and Sentences ① Seeing each other late, only Jingting Mountain.

(2) overlooking the Dongting mountains and rivers, a green snail in a silver plate. (3) At sunrise, the river is redder than the fire, and in spring, the river is as green as blue.

5. Rhetoric of Ancient Poetry ① Personification: Seeing each other late, only Jingting Mountain. ② Contrast: At sunrise, the river is redder than the fire, and in spring, the river is as green as blue.

(3) metaphor: there is no windless mirror on the pool surface-metaphor (pool surface) and (no polished bronze mirror). Looking at Dongting Lake, there is a green snail in the silver plate-Bi (Dongting Lake) Bi (silver plate); Compare (Junshan) to (green snail).

6. Similarities and differences between ancient poems are the same: 1, the authors are in the same dynasty (both written by poets in the Tang Dynasty) 2, the scenery and place are the same (both belong to the south of the Yangtze River) 3, the contents of poems are the same (both write scenery and are lyrical) but different: 1, the genre forms are different (the first two poems are poems and the last one is a word) 2, the poets feel different. 3. Different expression techniques (the first one mainly adopts anthropomorphic techniques, the second one is clever in metaphor, and the third one is very strong in contrast. )

7. Ancient Poetry Imagine me sitting alone in Jingting Mountain. The environment here is very quiet. Suddenly, several twittering birds flew in the sky, flying farther and farther until they disappeared. Lonely clouds are floating in the sky, unwilling to stay, and slowly drifting away.

Only when I look at the high Jingting Mountain and Jingting Mountain looks at me silently, neither of us will feel bored. Who can understand my lonely mood at this time, only this beautiful Jingting Mountain.

On a night with few stars in autumn, I walked by Dongting Lake and looked at it from a distance. Silver moonlight shines on the mirror-level lake, and the soft moonlight blends with the lake. The whole lake looks like a veil. In the twilight, that Junshan looks like a green snail in a silver plate, which is very attractive. I was intoxicated by the charming scenery.

Spring returns to the earth and flowers are in full bloom. How beautiful the scenery in Jiangnan is. I am already familiar with this picturesque scenery. Whenever the sun rises from the river, the flowers on the river are more fiery red, and the green river is clean. Ming Che is as blue as grass.

How can one not miss Jiangnan? Lesson 23 Collection of Ancient Poetry Analysis 1, ancient poetry-April in the country (Weng Juan in Song Dynasty)-shows the poet's love and praise for the pastoral scenery, as well as praise for the working people and working life. (1) Poem: The mountains and rivers are white and the rain is like smoke in the sound of rules.

In April, there were few idle people in the countryside, and sericulture was planted in the fields. ② Poetry: The vilen on the hillside is lush, but the water in the rice fields is so bright that the sky shines, cuckoos crow and the sky is misty and rainy.

When April comes, farmers are busy with farm work and no one is idle. Just after sericulture, it is necessary to transplant rice seedlings again. 2. The ancient poem "Miscellaneous Stories of Four Seasons" (Fan Chengda, Song Dynasty)-The poet described the scene of rural farmers farming and children working like adults, praised the industriousness of rural working people and expressed the author's love for innocent and lovely working people.

(1) Poetry: Come out during the day, harvest the fields at night, and the children in the village are in charge. Although the children don't plow and weave, they also learn a kind of melon in the shade of mulberry trees.

Poetry: Mow the ground during the day and rub hemp at night. Farmers and men are busy with their own affairs, and each has his own skills. Children know nothing about farming and weaving, and they imitate adults and learn to grow melons under mulberry trees.

3. The word "Fishing Songs" (Tang Zhang) shows the carefree life interest of the fisherman. Poetry: Egrets fly in front of Mount Cisse, peach blossoms and flowing water make mandarin fish fat.

An old man in the bank, wearing a green bamboo hat raincoat and a green raincoat, braved the wind and rain and fished leisurely. He was fascinated by the beautiful spring scenery and didn't even go home in the rain. ② Poetry: Egrets spread their wings near Mount Cisse, mandarin fish are full in the stream, and peach blossoms bloom on the shore.

People who wear green hats and hemp fibers and fish in the oblique wind and drizzle don't want to go home. Common sense of literature, key points 1, sitting alone in Jingting Mountain-Li Bai was a great romantic poet in the Tang Dynasty, whose words were too white, and later he was called a poetic fairy.

2. Wang Dongting —— Liu Tang Yuxi Zimeng, a writer and philosopher in the Tang Dynasty. Also known as "Bai Liu" with Bai Juyi.

3. Memory of Jiangnan ── Tang Bai Juyi is a word, and Memory of Jiangnan is a epigraph name. 4. April in the Country-Song Weng Juan shows the poet's love and praise for the rural scenery, and also shows his praise for the working people and working life.

5. Four Seasons Pastoral-Song Fan Chengda praised the industriousness of rural working people and expressed the author's love for innocent and lovely children. 6. The fisherman's song-Zhang Tang He Zhi has a beautiful artistic conception, which shows the fisherman's carefree interest.

Enter the text 1. Scenic features 1. Mountains and rivers in Guilin-wonders, quiet and green II. Shuanglong Cave-the majestic, thrilling and magical Tianshan Mountain in March and July-wonderful and charming. The sea-magnificent 5. West Lake-Level as a mirror 6. Mount Tai-a majestic mountain peak. Xiangshan-

6. 20 words in the fourth grade of scientific common sense

The mystery of automatic rotation

Thinking: Why do cartons full of water rotate?

Materials: empty milk box, nails, 60 cm long rope, sink, water.

Operation:

1. Punch five holes in the empty milk box with nails.

2. One hole is in the middle of the top of the carton, and the other four holes are in the lower left corner of the four sides of the carton.

3. Tie a rope about 60 cm long on the top hole.

4, put the carton on the plate, open the carton mouth, quickly fill the carton with water.

5. Lift the rope at the top of the carton by hand, and the carton rotates clockwise.

Description: the water flow produces equal and opposite forces, and all four corners of the carton are pushed by this force. As this force acts on the lower left corner of each side, the carton rotates clockwise.

Create:

1. If a hole is punched in the center of each side, how will the carton rotate?

2. If the hole is located in the lower right corner of each side, which direction will the carton rotate?

Boat and paddle

Thinking: Have you ever seen boating? Rowing by yourself? Do you know why the ship is moving on the water?

Materials: scissors 1, cardboard 1, rubber band 1, washbasin and water 1 basin.

Process:

1. Cut the cardboard into about 12cm * 8cm long.

2. One end of the bow is cut into a sharp shape, and the other end is cut out of the center of the stern by about 5 cm.

3. Cut a piece of cardboard about 3cm * 5cm to make ship pulp.

4. Tie a rubber band at the stern and tie an oar.

5. Turn the cardboard paddle counterclockwise and tighten the rubber band, and the boat will move forward.

6. If you turn the cardboard paddle clockwise to tighten the rubber band, the boat will move backwards.

Description:

1, the rubber band twists in different directions, but the ship's direction is just the opposite.

2. The power of paper boat movement comes from the energy of rubber band torsion.

7. Little knowledge of science in grade four (I)

Simple and easy-to-learn scientific knowledge The mystery of automatic rotation: Why do cartons filled with water rotate? Materials: empty milk cartons, nails, 60 cm long rope, sink, water operation: 1. Punch five holes in the empty milk box with nails. 2. One hole is in the middle of the top of the carton, and the other four holes are in the lower left corner of the four sides of the carton. 3. Tie a rope about 60 cm long on the top hole. 4. Put the paper box on the plate, open the paper box mouth and fill the paper box quickly.

Because this force acts on the lower left corner of each side, the carton rotates clockwise: 1. If you punch holes in the center of each side, how will the carton rotate? 2. If the hole is located in the lower right corner of each side, which direction will the carton rotate? Thinking: Have you ever seen boating? Rowing by yourself? Do you know why the ship is moving on the water? Material: 1 scissors, 1 cardboard, 1 rubber band, washbasin and 1 basin water technology: 1. Cut the cardboard about 12 cm *8 cm long. 2. Cut one end into a sharp shape as a bow. Cut a gap of about 5 cm from the center of the other end to make the stern. 3. Cut a piece of cardboard boat pulp about 3 cm *5 cm. 4. Cover the stern with a rubber band and tie it to the oar. 5. Turn the cardboard paddle counterclockwise and tighten the rubber band, and the boat will move forward. 6. If you turn the cardboard paddle clockwise and tighten the rubber band, the boat will move backwards. Description: 1, when the rubber band is twisted in different directions, the ship will travel in the opposite direction. 2. The power of paper boat movement comes from the energy of rubber band torsion.