100 points reward helps out some scientific topics below grade seven.
1. Some students said, "A stationary object has no inertia, while a moving object has inertia." Student B said: "When an object has no force or is subjected to a balanced force, it has no inertia. When it changes from static to motion or from motion to static, it has inertia." Are these two students right? Why?
Answer:
Both students are incorrect, because inertia is the inherent property of all objects, and all objects have inertia at any time and under any circumstances.
The hammer is loose. Grasp the hammer with your hand and touch the handle of the hammer several times on the ground, and the hammer will be tightly sleeved on the handle. Why?
Answer:
Because the hammer head and the hammer handle move downward together, when the hammer handle hits the ground, it is forced to stop moving. Because of inertia, the hammer still maintains its original motion state and will be tightly sleeved on the hammer handle.
3. In the long jump competition, why don't athletes stand at the jumper and take off directly, but run for a certain distance and then take off after reaching the jumper?
Answer:
Run-up can make athletes have a higher take-off speed when they reach the jump line, so they can fly farther and jump farther in the air when they take off from the ground.
4. When taking pictures of clothes, why can I take the dust off the clothes?
Answer:
The force on the clothes changes from static, while the dust remains static.
On the bus, you often hear the voice prompt of "the vehicle is entering the station, please hold it well and sit well". Please use physical knowledge to explain the truth.
Answer:
When the bus stops and the brakes slow down, passengers will keep their original state of motion because of inertia and fall forward, which is prone to accidents.
6. Xiaoli does experiments at home by herself. She put a boiled egg on the cardboard covering the water glass. When she suddenly tapped the cardboard with her finger, she saw the cardboard fly out and the egg fell into the cup. Please briefly explain the reasons in combination with your physical knowledge.
Answer:
Because all objects have inertia. Eggs and cardboard were originally static. When the finger suddenly touches the cardboard, the cardboard flies forward due to the thrust. However, the eggs remain in the original static state because of inertia, and because the cardboard has flown out and there is no support for the eggs, the eggs fall into the water glass under the action of gravity.
7. Where will the passengers who jump out of the train carriage moving in a straight line at a constant speed land? Why?
Landing at the jump point. Because the passenger used to move in a straight line with the train at a constant speed, when he jumped up, he remained at the jumping point after falling because of inertia.
8. Read the following news report. There is a scientific mistake in it. Please find it.
At 6: 30 this morning, the bus No.21in this city was in distress and the driver braked suddenly. Three passengers sitting in the back row were injured because they suddenly lost their inertia and rushed forward.
Answer:
Lose inertia
9. When you slip on the ice, you always lie on your back, but when you fall down during running, you always lie on the ground. Please use the inertia knowledge you have learned to explain the difference between the two phenomena.
Answer:
When sliding on the ice, the feet are forced to change their state of motion, and the upper body keeps its original state of motion because of inertia, so when sliding, it always slides on its back; Fast runners are forced to change their original forward motion state with their feet, and their bodies keep their original forward motion state due to inertia. Therefore, when they fall, they always lie forward on the ground.
10. How to distinguish raw eggs from cooked eggs by the law of inertia?
Answer:
Let two eggs spin on a smooth horizontal surface. The inside of raw eggs is liquid, and the shell rotates, while the internal liquid quickly stops rotating due to inertia. Cooked eggs are solid, rotating at the same speed inside and outside, and can rotate for a long time before stopping.
Conditions for the Balance of Two Forces (Question 10)
1. The TV set placed on a horizontal desktop is subjected to mutually balanced forces:
A. the gravity of the TV and the supporting force of the desktop to the TV;
B. the gravity of TV and the pressure of TV on the desktop;
C. The pressure of the TV set on the desktop and the support of the desktop on the TV set;
D. the pressure of TV on the desktop and the gravity of the table.
A: A.
2. Hold the soda bottle by hand, so that the soda bottle will not slide. This is because:
A. The grip strength of the hand is greater than the gravity of the soda bottle;
B. the grip strength of the hand is equal to the gravity of the soda bottle;
C. The friction of feeding soda bottles by hand is greater than the gravity of the bottles;
D. The friction of the hand against the soda bottle is equal to the gravity of the bottle.
Answer: d
3. The pencil box placed on the horizontal desktop remains motionless, and the following pairs of forces are balanced:
A. the gravity of the pencil box and the supporting force of the desktop;
B. the supporting force of the pencil case and the pressure of the pencil case on the desktop;
C. the supporting force of the pencil box and the pressure of the table on the ground;
D the gravity of the pencil box and the pressure of the pencil box on the desktop.
A: A.
There is a wire hanging from the ceiling, and an electric light is hung on it. Among the following pairs of forces, the one that belongs to the balance force is:
A, the pull of the wire to the electric lamp and the pull of the electric lamp to the wire;
B, the pull of the electric lamp on the wire and the gravity of the earth on the electric lamp;
C, the pull of the wire to the electric lamp and the gravity of the earth to the electric lamp;
D, the tension of the wire to the ceiling and the tension of the wire to the lamp.
Answer: c
5. Regarding the balance force, the following statement is correct:
A. an object must remain stationary under the action of a balancing force;
B. The three elements of two forces acting on an object are exactly the same, and these two forces must be balanced forces;
C. an object is subjected to gravity and tension, which are in opposite directions, and they must be balanced forces;
D. A moving object must keep a uniform linear motion under the action of a balancing force.
Answer: d
6. A classmate pushes a car parked on a straight road with horizontal thrust, but it doesn't push, so the following statement is correct:
A. Because the thrust is less than the gravity of the car, the car is not pushed;
B. Because the thrust is less than the resistance of the trolley, the trolley is not pushed;
C. Although the car is not propelled, the thrust must be equal to the gravity of the car;
D. Although the trolley is not pushed, the thrust is equal to the resistance of the trolley.
Answer: d
7. After learning the knowledge of "sports and strength", I have the following understanding of nicknames, among which the correct one is:
An object will move when it is strongly acted on, and will stand still when it is not acted on;
B objects that are not in contact with each other must have no force;
C when an object is stressed, its motion state will definitely change;
D. when the motion state of an object changes, there must be a force at work.
Answer: d
8. The train travels in a straight line at a constant speed on the straight line railway because:
A. the train is not affected by external forces;
B. The traction of the train is greater than the resistance it receives;
The traction and resistance of C train are a pair of balancing forces;
There was no resistance on the train.
Answer: c
9. When lifting an object with a weight of 20,000 with a crane, it first rises at a uniform speed of 1m/s, and then falls at a uniform speed of 1m/s, so the correct statement about the tension on the object is:
A. when rising at a uniform speed, it is greater than 20000N n.
B. Both uniform rising and uniform falling are equal to zero;
C. Both uniform rising and uniform falling are equal to 20000N N.
D. less than 20000N when falling at a constant speed.
Answer: c
10. Regarding the relationship between motion and force, the following statement is correct:
A. As long as an object is subjected to a force, its speed will change;
B. If the force is too small, the motion state of the object cannot be changed;
C. An object subjected to a balancing force will remain at rest forever;
D. when the motion state of an object changes, it is bound to be acted by force.
Answer: d
The rotation of the earth (6 questions)
1. How to explain "sitting on the ground and traveling 80,000 miles a day, patrolling the sky and watching the sea"?
Answer:
This is a poem in Mao Zedong's poem "Seeing the Sorrow God", which refers to the situation on the equator. The circumference of the equator of the earth is about 40000 kilometers. The earth rotates, and the linear speed of rotation on the equator is about 80 thousand miles a day, that is, "sitting on the ground and walking 80 thousand miles a day"; Looking at the celestial bodies outside the earth on the earth, all the celestial bodies seem to be located on a sphere centered on the observer. With the rotation of the earth, the number of sun, moon and stars seen on the equator is the largest, that is, "seeing thousands of rivers from afar." You can see 88 constellations all day at the equator, which can't be achieved at other latitudes.
2. If the camera is fixed, aimed at the starry sky near Polaris, and exposed for a long time (about 10 hour), you can get a picture of the starry sky near Polaris (a ring diverging from the center, with different colors for each ring and segment, like just visiting in science fiction films). Why do the stars in the photo show such a trajectory?
Answer:
This is related to the spatial orientation of the earth's rotation axis. Its northern end always points to the vicinity of Polaris, and the earth revolves around its axis of rotation from west to east. For example, if the camera is fixed and aimed at the starry sky near Polaris, the center of light is Polaris. For the earth, the spatial position of stars is considered to be fixed. The star in the photo will have an arc trajectory, which is actually due to the rotation of the earth, and the camera moves with the earth. As a result, the star seems to have moved. People on the earth watch the movement of the stars, but their apparent movement rotates counterclockwise.
3. Why is the earth not a right sphere?
Answer:
When the earth rotates, all the particles on the ball are in circular motion around the earth axis. Inertial centrifugal force is generated. This centrifugal force increases with the increase of the radius of the object from the earth axis, that is to say, the inertial centrifugal force decreases gradually from the equator to the poles. It makes the earth gradually expand from the poles to the equator, and the long-term effect makes the earth an ellipsoid with slightly flat poles and slightly bulging equator.
We live on the earth and watch the sunrise and sunset every day. So is the earth moving or the sun moving?
Answer:
When we sit in the car and look out, you will see that the tree outside the car will retreat, that is, the direction of the tree you see is opposite to the direction of our actual movement. Similarly, we live on the earth, because the direction of our earth's movement is from west to east, so we will see that the direction of the sun's movement is from east to west.
5. Explain the alternation of day and night.
Answer:
The rotation of the earth produces the phenomenon of alternating day and night. Because the earth is opaque, the side facing away from the sun is daytime, and the side facing away from the sun is night. The earth rotates, making day and night appear alternately.
6. There is a river from east to west in the northern hemisphere, which generally appears: the erosion on the north bank is greater than that on the south bank; The south bank accumulates faster than the north bank. Why? explain
Answer:
A river flowing from east to west in the northern hemisphere is influenced by the geostrophic bias due to the rotation of the earth (the velocity direction in the northern hemisphere is positive, but it is opposite in the southern hemisphere). The impact to the right is actually the impact to the north, so the erosion on the north bank is greater than that on the south bank, and the accumulation on the south bank is faster than that on the north bank.
Science on the Calendar (Question 10)
1. There are 52 real cards in the poker design. What do the four colors of diamonds, hearts, spades and clubs represent respectively?
Answer:
Playing cards have 52 weeks in a year, so 52 real cards are designed; Playing cards are designed as diamonds, hearts, spades and clubs, because a year can be divided into four seasons: spring, summer, autumn and winter.
2. The ancient calendar in China was marked by "trunk and branch". Do you know what heavenly stems and earthly branches includes?
Answer:
Ten-day cadres: A, B, C, D, E, G, Xin, Ren and Gui.
Twelve earthly branches: Zi, Ugly, Yin, Mao, Chen, Ji, Wu, Wei, Shen, You, Xu and Hai.
3. Why is there a leap year?
Answer:
The earth's cycle around the sun is 365 days, 5 hours, 48 minutes and 46 seconds. The Gregorian calendar has an average of only 365 days a year, which is about 0.2422 days shorter than the tropical year, and the remaining time is about four years. So February 4th is added with 1 day, making the calendar year of that year 366 days, and this year is a leap year.
Please name the 24 solar terms in our country.
Answer:
Beginning of spring, rain, fright, vernal equinox, Qingming, Grain Rain;
Long summer, Xiaoman, Mangzhong, Summer Solstice, Xiaoshu, Dashu;
Beginning of autumn, Chu Shu, Bailu, Autumnal Equinox, Cold Dew, First Frost;
Beginning of winter, light snow, heavy snow. Winter solstice, slight cold, severe cold.
5. When was the earliest year that China used the Gregorian calendar?
Answer:
19 1 1 After the success of the Revolution of 1911, it was decided to adopt the international Gregorian calendar, so the New Year's Day of the lunar calendar was changed to "Spring Festival" and 1 day of the Gregorian calendar was called New Year's Day. When New China was founded, the "AD Chronology Law" was officially used, and the annual Gregorian calendar 1 was designated as New Year's Day.
6. Gregorian calendar date is based on ()
A. based on the rotation period of the earth.
C. According to the phase change of the moon D. According to the phase change of the moon and the period of revolution of the earth.
Answer: b
7. Which of the following years is a leap year ()
In 2002
Answer: d
In 2003, Xiao Ming was 9 years old, and there was no birthday this year. In the next few years, Xiao celebrated his birthday.
A.2004 b. 2005 c. 2006 d. 2007
A: A.
9. There are mainly three kinds of calendars, namely, calendars based on the cycle of moon phases. At present, the most common calendar in the world is. The calendar in our country consists of two parts: the solar calendar and the lunar calendar, in which the solar calendar is a calendar, including the lunar calendar.
Answer:
Lunar calendar, solar calendar, lunar calendar, solar calendar, solar calendar, month, day, week, lunar calendar.
10. It is the twenty-four solar terms that the working people in ancient China divided the four seasons into cycles.
Division is an important part of the lunar calendar.
Answer:
Twenty-four solar terms, the earth's orbit around the sun.