“gravity”的概念、定义、翻译、参考文献-科学参考

gravity

Physics

The phenomenon associated with the gravitational force acting on any object that has mass and is situated within the earth’s gravitational field. The weight of a body (see mass) is equal to the force of gravity acting on the body. According to Newton’s second law of motion F=ma, where F is the force producing an acceleration a on a body of mass m. The weight of a body is therefore equal to the product of its mass and the acceleration due to gravity (g), which is now called the acceleration of free fall. By combining the second law of motion with Newton’s law of gravitation (F=GM₁M₂/d²) it follows that: g=GM/d², where G is the gravitational constant, M is the mass of the earth, and d is the distance of the body from the centre of the earth. For a body on the earth’s surface g=9.806 65 m s⁻².

A force of gravity also exists on other planets, moons, etc., but because it depends on the mass of the planet and its diameter, the strength of the force is not the same as it is on earth. If F_e is the force acting on a given mass on earth, the force F_p acting on the same mass on another planet will be given by:

$F_{p} = F_{e} d_{e}^{2} M_{p} / M_{e} d_{p}^{2},$

where M_p and d_p are the mass and diameter of the planet, respectively. Substituting values of M_p and d_p for the moon shows that the force of gravity on the moon is only 1/6 of the value on earth.

https://www.nasa.gov/centers/jpl/missions/grace.html The home page of the NASA/JPL Gravity Recovery and Climate experiment to make precise measurements of the earth’s gravitational field

Mathematics

Near the Earth’s surface, a body experiences the gravitational force between the body and the Earth, which may be taken to be constant. The resulting acceleration due to gravity is −gk, where k is a unit vector directed vertically upwards from the Earth’s surface, assumed to be a horizontal plane. The constant g, which is the magnitude of the acceleration due to gravity, is equal to GM/R², where G is the gravitational constant, M is the mass of the Earth and R is the radius of the Earth. Near the Earth’s surface, the value of g may be taken as 9.81 ms⁻², though it varies between 9.78 ms⁻² at the equator and 9.83 ms⁻² at one of the poles.

Space Exploration

A force of attraction that arises between objects by virtue of their masses (see gravitational force). The larger the mass of an object the more strongly it attracts other objects. On Earth, gravity causes objects to have weight; it accelerates objects (at 9.8 m s^–2) towards the centre of the Earth, the ground preventing them falling further.
The Earth's gravity also attracts the Moon towards the Earth, keeping the Moon in orbit around the Earth. The Moon's gravity is one-sixth that of the Earth, so objects on the Moon weigh less than on Earth. The Sun contains 99.8% of the mass of the Solar System, and the resulting large force of gravity keeps the planets of the Solar System in orbit around the Sun.
Spacecraft launched from Earth must overcome the force of gravity before entering space. This is achieved by using rocket boosters at various stages of the launch. The spacecraft needs an acceleration of three times that of gravity (3 g).
escape velocity
This is the velocity that a projectile or spacecraft needs to reach in order to escape from a gravitational field. The escape velocity from the surface of the Earth is about 40 000 kph; that from the Moon (with one-sixth the gravitational pull of the Earth) is about 8 500 kph.
relativity
German-born US physicist Albert Einstein's general theory of relativity treats gravitation not as a force but as the curvature of space-time around a body. Relativity predicts the bending of light and the redshift of light in a gravitational field; both have been observed. Another prediction of relativity is that gravitational waves should be produced when massive bodies are violently disturbed. These waves are so weak that they have not yet been detected with certainty, although observations of a pulsar (which emits energy at regular intervals) in orbit around another star have shown that the stars are spiralling together at the rate that would be expected if they were losing energy in the form of gravitational waves.

Chemical Engineering

The force that pulls a body towards the centre of the Earth. According to Newton’s second law of motion, the weight of an object is the product of its mass and gravitational acceleration F = mg. It varies with latitude and elevation above sea level. For precise calculations, the gravitational acceleration is taken to equal to 9.806 65 m s⁻².

Suspensions of small particles can be separated from solutions by the force of gravity as in the process of sedimentation. The process, however, tends to be slow. Centrifugation is a process used to apply a far higher ‘gravitational’ force to the particles, increasing the rate of separation.

单词	gravity
释义	gravity Physics The phenomenon associated with the gravitational force acting on any object that has mass and is situated within the earth’s gravitational field. The weight of a body (see mass) is equal to the force of gravity acting on the body. According to Newton’s second law of motion F=ma, where F is the force producing an acceleration a on a body of mass m. The weight of a body is therefore equal to the product of its mass and the acceleration due to gravity (g), which is now called the acceleration of free fall. By combining the second law of motion with Newton’s law of gravitation (F=GM₁M₂/d²) it follows that: g=GM/d², where G is the gravitational constant, M is the mass of the earth, and d is the distance of the body from the centre of the earth. For a body on the earth’s surface g=9.806 65 m s⁻². A force of gravity also exists on other planets, moons, etc., but because it depends on the mass of the planet and its diameter, the strength of the force is not the same as it is on earth. If F_e is the force acting on a given mass on earth, the force F_p acting on the same mass on another planet will be given by: $F_{p} = F_{e} d_{e}^{2} M_{p} / M_{e} d_{p}^{2},$ where M_p and d_p are the mass and diameter of the planet, respectively. Substituting values of M_p and d_p for the moon shows that the force of gravity on the moon is only 1/6 of the value on earth. https://www.nasa.gov/centers/jpl/missions/grace.html The home page of the NASA/JPL Gravity Recovery and Climate experiment to make precise measurements of the earth’s gravitational field Mathematics Near the Earth’s surface, a body experiences the gravitational force between the body and the Earth, which may be taken to be constant. The resulting acceleration due to gravity is −gk, where k is a unit vector directed vertically upwards from the Earth’s surface, assumed to be a horizontal plane. The constant g, which is the magnitude of the acceleration due to gravity, is equal to GM/R², where G is the gravitational constant, M is the mass of the Earth and R is the radius of the Earth. Near the Earth’s surface, the value of g may be taken as 9.81 ms⁻², though it varies between 9.78 ms⁻² at the equator and 9.83 ms⁻² at one of the poles. Space Exploration A force of attraction that arises between objects by virtue of their masses (see gravitational force). The larger the mass of an object the more strongly it attracts other objects. On Earth, gravity causes objects to have weight; it accelerates objects (at 9.8 m s^–2) towards the centre of the Earth, the ground preventing them falling further. The Earth's gravity also attracts the Moon towards the Earth, keeping the Moon in orbit around the Earth. The Moon's gravity is one-sixth that of the Earth, so objects on the Moon weigh less than on Earth. The Sun contains 99.8% of the mass of the Solar System, and the resulting large force of gravity keeps the planets of the Solar System in orbit around the Sun. Spacecraft launched from Earth must overcome the force of gravity before entering space. This is achieved by using rocket boosters at various stages of the launch. The spacecraft needs an acceleration of three times that of gravity (3 g). escape velocity This is the velocity that a projectile or spacecraft needs to reach in order to escape from a gravitational field. The escape velocity from the surface of the Earth is about 40 000 kph; that from the Moon (with one-sixth the gravitational pull of the Earth) is about 8 500 kph. relativity German-born US physicist Albert Einstein's general theory of relativity treats gravitation not as a force but as the curvature of space-time around a body. Relativity predicts the bending of light and the redshift of light in a gravitational field; both have been observed. Another prediction of relativity is that gravitational waves should be produced when massive bodies are violently disturbed. These waves are so weak that they have not yet been detected with certainty, although observations of a pulsar (which emits energy at regular intervals) in orbit around another star have shown that the stars are spiralling together at the rate that would be expected if they were losing energy in the form of gravitational waves. Chemical Engineering The force that pulls a body towards the centre of the Earth. According to Newton’s second law of motion, the weight of an object is the product of its mass and gravitational acceleration F = mg. It varies with latitude and elevation above sea level. For precise calculations, the gravitational acceleration is taken to equal to 9.806 65 m s⁻². Suspensions of small particles can be separated from solutions by the force of gravity as in the process of sedimentation. The process, however, tends to be slow. Centrifugation is a process used to apply a far higher ‘gravitational’ force to the particles, increasing the rate of separation.
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escape velocity

relativity