The determination of the Earth's mass provides a basis for determining the mass of other celestial bodies.From the mass of the earth, the average density of the earth is about 5.52g/cm3.At the same time, the mass of the earth is also the unit for measuring the mass of planets, with the symbol "M ⊕".
It is generally recognized that the earth mass is 5.965 × 10 ^ 24kg
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[UK《The Observer》Report] The calculation results show that the earth'smass ratioOriginally thought to be much lighter.The result of this calculation is far beyond physicists' expectations.
The two physicists said that they had obtained the most accurate calculation result of the gravitational constant affecting each planet so far.Although people have long known the speed of light and the speed of sound, the scientific community has been unable to solve the gravitational constant.knowGravitational constantWe can calculate the mass of the planet.
For astronomers and physicists, this breakthrough is of great significance.britainUniversity of BirminghamPhysicist Dr. Spike said that the calculation result "greatly exceeded the scientists' expectations".
The earth where humans live is a very huge sphere.Who was the first person to measure the mass of the earth?He's a British scientistHenry Cavendish (1731-1810).In 1798, he passed an ingenious experiment,Indirect measurementThe huge mass of the earth is known as "the first person to call the earth".
Unable to overcome difficult problems
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On October 10, 1731,Henry Cavendish Born in a noble family in England, this family has a very prominent position and is rich.But when he was young, he loved reading and was full of fantasy,Thirst for knowledgeStrong.The solid foundation he laid in his youth played a great role in his achievements in science in his life.
Cavendish lived in the era of rapid development of natural science, but also faced many "problems", of which the most famous one was "weighing the mass of the earth".At that time, it was known through measurement and calculation that the radius of the earth was about 6400km;EarthlySurface areaThrough measurement and calculation, it is known that it is about 5.1 × 10 ¹ ∨ square meters;Through calculation, the volume of the earth is about 1.08 × 10 ² ¹ cubic meters, which is extremely huge.Therefore, people are eager to know: what is the mass of the earth?
At that time, many scientists tried to find a way to "call the earth".Someone proposed to use the calculation method: the earth volume has been known, then try to find out its average density, and then use the formula of mass=density * volume to find out the earth mass.This method of using the density formula of physics has some reasons.laterEarth's atmosphereThe mass of is measured and calculated by this method.The density of the atmosphere decreases with altitude,Air quality90% is concentrated within 15 km above the surface. After careful measurement and calculation, we can know that the mass of the earth's atmosphere is about 5.3 × 10 ² ¹ g (accounting for aboutTotal massOne millionth of).
However, this method of calculating physical density formula cannot calculate the mass value of the earth entity.Because the physical structure of the earth is very complex, the density of each part of the earth is different and very different, and the density of the earth's center cannot be known at all.So someone asserted: "Human beings will never know the quality of the earth!"
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The first challenge to this sentence is young scientistsNewton。In 1687, he discoveredLaw of universal gravitation: "Any two objects attract each other, and the gravity is proportional to the product of the masses of these two objects, and inversely proportional to the square of their center distance." Newton was pleased to find that the mass of the earth can be calculated using this formula of the law of universal gravitation!You see: in the formula, M represents the mass value of the earth, and m represents a known value on the groundMass of objectValue, r is the distance between their centers (i.eEarth radiusThe value of the universal gravitation f is the value of the gravity on the object m.This can calculate the value of the earth mass M!
However, careful readers find that there is another condition for using the formula of "law of universal gravitation": the value of "coefficient of universal gravitation" G must be obtained.In other words, it must be on the grounddirect measurement Find out the value of gravity between two objects.
Newton carefully designed several experiments to measure the gravity between two objects on the ground, but failed. After rough calculation, Newton found that the gravity between ordinary objects was so small that it could not be measured at all.Disappointed, Newton, who has become everyone's last hope for measuring the earth's mass, also announced publicly that it would be futile to try to use the law of universal gravitation to calculate the earth's mass on the ground by measuring gravity!
In 1750, French scientist Bouguer set up a movement toSouth AmericaOfEcuador, climb to the steep top of Qinbo Lacuo Mountain, and hang one along the cliffPlumb line。He thought: the mass of the shot is known, and the mass of the mountain can be calculated. As long as the deviation angle of the shot due to the attraction of the mountain is measured, the gravity between the mountain and the shot can be known, and then the mass of the earth can be calculated."Plumb line method"Experimental principleYes, but I failed many times.becausemountain breezeAnd the influence of various vibrations is far more than the micro gravity between the mountain and the shot put. The experiment did not obtain any meaningful data.
In 1774, British scientist Neville·MaskilinOn a steep cliff in Perth County, the "plumb line method" was used to carefully measure and take some measures to avoid wind and vibration. However, the "plumb line method" failed.
Micro gravity is amplified
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The scientific problem of "calling the earth" strongly attracted young Cavendish.Cavendish graduated fromUniversity of CambridgeFrom then on, we embarked on the road of scientific research.He was the first to find outhydrogenElement;By hydrogen and oxygenSpark dischargeGetting water;Obtained by spark discharge of oxygen and nitrogennitric acid... known as "the most effective machine", joined at the age of 29Royal SocietyAnd become an influential scientist.But Cavendish never forgot this famous scientific "problem": call the earth!
On the basis of previous research results, Cavendish began a new climb.What hard efforts did he make?
"If a worker wants to do his job well, he must first sharpen his tools.".In 1750, Cavendish, only 19 years old, heard a news that John Michel of Cambridge University used a new force measuring method when studying magnetic force:magnetic needleLift it from the middle and use the torsion degree of the string to express the force.Cavendish made a special trip to ask for advice, carefully observed and carefully studied this device.
Cavendish used Michel's device to design a new method to measure the micro gravity. Two small shot balls were installed at both ends of a slender rod to make a "dumbbell" like thing. A thin wire was used to lift the "dumbbell" from the middle. During the experiment, two large shot balls were used to approach the small shot respectively.Due to the effect of universal gravitation between big and small shot put, the "dumbbell" will rotate slightly. By carefully measuring the degree of twisting of the filament, you can calculate the gravitation between big and small shot put, and then calculate the mass of the earth.But he failed in many experiments.Why?We know that when two 1kg shot put are 10cm apart, the attraction is only one billionth of a kilogram!It is not easy to measure such a tiny force.
Cavendish fell into a long-term depression. He thought that the filament must have twisted during the experiment, but it was too small to be observed by the naked eye.Can you amplify the tiny twist?In what way?Cavendish meditated.One day, he wentroyal society On the way to the activity, I saw several children playing games: reflecting with the small mirror in their handssunlight, look at each other and play. As long as the small mirror is slightly rotated, the position of the distant light spot will change greatly.Cavendish's mind burst out a bright spark: "Small mirror!light spot！Small mirror!light spot！”He let out a cry.
Cavendish immediately ran back to the laboratory and began to modify the instrument. He fixed a small mirror on the filament to reflect a beam of light onto a scale.In this way, as long as the filament has an extremely small rotation,a scaleThe light spot on the instrument will move obviously, and the sensitivity of the instrument will be greatly enhanced.Cavendish further managed to solve various interference problems of the instrument, such as the influence of air flow and vibration.This set of improved instrument that can measure micro force is named“Torsion scale”, still playing a role in precision experiments.
Weigh out the mass of the earth
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Cavendish utilization“Torsion scale”Finally, he measured the mass of the earth. In 1798, he announced the huge mass value of the earth. At that time, he was already white haired and 67 years old.What is the mass of the earth?It is about 5.965 × 10 ^ 24kg, which is about 60 trillion tons.
When the mass of the earth is known, the average density of the earth can be calculated: the average density of the earth measured in modern times is about 5.517g/cm3;andSurface of the earthThe density is only 2.5-3g/cm3, so we can calculate that the density in the center of the earth is 7-8g/cm3, which is much larger than the surface of the earth and may be composed of heavy materials such as iron and nickel.
Soon, the same method was used to measure the more huge mass of the sun, which is 300000 times the mass of the earth, 2 × 10 ³ º kg.nextsolar systemThe mass of other planets also graduallyMeasuredCome out.Law of universal gravitationI keep gettingphysical experiment The value of the universal gravitation coefficient G is also measured more and more accurately, becoming one of the important physical parameters and playing an extremely important role in modern aerospace technology.Cavendish“Torsion scale”The experimental results have effectively promoted the development of science and technology.
On March 10, 1810, Cavendish was in EnglandLondonHe died and never married.He and the "torsion balance" designed by him were recorded in the history of science and technology, and were praised as "the first person to call the earth"!In memory of thisBig scientist, specially erected a monument for him.University of CambridgeHe also named the laboratory where Cavendish worked asCavendish Laboratory This laboratory has produced many famous physicists.Cavendi was a scholar who lived and worked until he was 79 years old and the night before his death.He has won many nicknames in his life, such as "science geek", "science giant", "the richest scholar, the most erudite millionaire", etc.His spirit of diligent study, good thinking and bold exploration is always worth learning.
