重力 | 定義、物理学、事実

Gravity | Definition, Physics, & Facts | Britannica Ask the Chatbot Games & Quizzes History & Society Science & Tech Biographies Animals & Nature Geography & Travel Arts & Culture ProCon Money Videos gravity Introduction Development of gravitational theory Early concepts Newton’s law of gravity Weight and mass Interaction between celestial bodies Potential theory Effects of local mass differences Weighing the Earth Acceleration around Earth, the Moon, and other planets Variations in g Changes due to location Changes with time Measurements of g Unit of gravity Absolute measurements Relative measurements Gravimetric surveys and geophysics The Moon and the planets Gravitational theory and other aspects of physical theory Field theories of gravitation Gravitational fields and the theory of general relativity The paths of particles and light Gravitational radiation Some astronomical aspects of gravitation Experimental study of gravitation The inverse square law The principle of equivalence The constant of gravitation The variation of the constant of gravitation with time Fundamental character of G References & Edit History Quick Facts & Related Topics Images & Videos At a Glance gravity summary Quizzes Physics and Natural Law All About Astronomy All About Physics Quiz Related Questions What are the basics of chemical reactions? What happens to chemical bonds when a chemical reaction takes place? How are chemical reactions classified? Why is light important for life on Earth? What different units of time do we use, and why are they important? print Print Please select which sections you would like to print: Table Of Contents CITE verified Cite While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Select Citation Style MLA APA Chicago Manual of Style Copy Citation Share Share Share to social media Facebook X URL https://www.britannica.com/science/gravity-physics Feedback External Websites Feedback Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login). Feedback Type Select a type (Required) Factual Correction Spelling/Grammar Correction Link Correction Additional Information Other Your Feedback Submit Feedback Thank you for your feedback Our editors will review what you’ve submitted and determine whether to revise the article. External Websites University of Oslo - Capillarity and Gravity Australian Academy of Science - Understanding gravity—warps and ripples in space and time West Texas A and M University - Science Questions with Surprising Answers - Why is there no gravity in space? Kwantlen Polytechnic University - Uniform Circular Motion and Gravity (PDF) ABC listen - The Science Show - Understanding gravity Space.com - Gravity: What is it? Physics LibreTexts - Gravity LiveScience - What is Gravity? CERN - Gravity and Zero Point Energy College of DuPage Digital Press - Conceptual Physics - Gravity OpenStax - Astronomy 2e - Spacetime and Gravity Britannica Websites Articles from Britannica Encyclopedias for elementary and high school students. gravity - Children's Encyclopedia (Ages 8-11) gravity - Student Encyclopedia (Ages 11 and up) gravitational lens A galactic cluster, about five billion light-years away, produces a tremendous gravitational field that “bends” light around it. This lens produces multiple copies of a blue galaxy about twice as distant. Four images are visible in a circle surrounding the lens; a fifth is visible near the center of the picture, which was taken by the Hubble Space Telescope. (more) gravity physics Ask Anything Quick Summary Homework Help Also known as: g-force, gravitation Written by James E. Faller Fellow, Joint Institute for Laboratory Astrophysics, University of Colorado, Boulder. James E. Faller All Fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors Last updated May 5, 2026 • History Britannica AI Ask Anything Quick Summary Table of Contents Table of Contents Quick Summary Ask Anything Top Questions What is gravity? How does gravity affect objects on Earth? Why do objects fall to the ground when dropped? Who discovered the law of gravity? How does gravity keep planets in orbit around the Sun? How does gravity change when you move further away from a planet? Show more Show less News • Physicists just found a tiny flaw in time itself • May 3, 2026, 9:40 AM ET (ScienceDaily) Show less gravity , in mechanics , the universal force of attraction acting between all bodies of matter. It is by far the weakest known force in nature and thus plays no role in determining the internal properties of everyday matter. On the other hand, through its long reach and universal action, it controls the trajectories of bodies in the solar system and elsewhere in the universe and the structures and evolution of stars, galaxies, and the whole cosmos . On Earth all bodies have a weight , or downward force of gravity, proportional to their mass, which Earth’s mass exerts on them. Gravity is measured by the acceleration that it gives to freely falling objects. At Earth ’s surface the acceleration of gravity is about 9.8 meters (32 feet) per second per second. Thus, for every second an object is in free fall, its speed increases by about 9.8 meters per second. At the surface of the Moon the acceleration of a freely falling body is about 1.6 meters per second per second. How gravity works on Earth and in the universe Learn about the concept of gravitational force in Newton's theory of gravitation. (more) See all videos for this article The works of Isaac Newton and Albert Einstein dominate the development of gravitational theory. Newton’s classical theory of gravitational force held sway from his Principia , published in 1687, until Einstein’s work in the early 20th century. Newton’s theory is sufficient even today for all but the most precise applications. Einstein’s theory of general relativity predicts only minute quantitative differences from the Newtonian theory except in a few special cases. The major significance of Einstein’s theory is its radical conceptual departure from classical theory and its implications for further growth in physical thought. The launch of space vehicles and developments of research from them have led to great improvements in measurements of gravity around Earth, other planets, and the Moon and in experiments on the nature of gravitation. Development of gravitational theory Early concepts Newton argued that the movements of celestial bodies and the free fall of objects on Earth are determined by the same force. The classical Greek philosophers, on the other hand, did not consider the celestial bodies to be affected by gravity, because the bodies were observed to follow perpetually repeating nondescending trajectories in the sky. Thus, Aristotle considered that each heavenly body followed a particular “natural” motion, unaffected by external causes or agents. Aristotle also believed that massive earthly objects possess a natural tendency to move toward Earth’s center. Those Aristotelian concepts prevailed for centuries along with two others: that a body moving at constant speed requires a continuous force acting on it and that force must be applied by contact rather than interaction at a distance. These ideas were generally held until the 16th and early 17th centuries, thereby impeding an understanding of the true principles of motion and precluding the development of ideas about universal gravitation. This impasse began to change with several scientific contributions to the problem of earthly and celestial motion, which in turn set the stage for Newton’s later gravitational theory. The 17th-century German astronomer Johannes Kepler accepted the argument of Nicolaus Copernicus (which goes back to Aristarchus of Samos ) that the planets orbit the Sun , not Earth. Using the improved measurements of planetary movements made by the Danish astronomer Tycho Brahe during the 16th century, Kepler described the planetary orbits with simple geometric and arithmetic relations. Kepler’s three quantitative laws of planetary motion are: Also called: gravitation (Show more) Key People: Isaac Newton Galileo Kip Thorne John Archibald Wheeler Pierre Bouguer (Show more) Related Topics: Lagrange point supergravity Gravity: From Apples to the Universe weight gravity anomaly (Show more) On the Web: Physics LibreTexts - Gravity (Apr. 21, 2026) (Show more) See all related content Britannica Quiz All About Physics Quiz The planets describe elliptic orbits, of which the Sun occupies one focus (a focus is one of two points inside an ellipse ; any ray coming from one of them bounces off a side of the ellipse and goes through the other focus). The line joining a planet to the Sun sweeps out equal areas in equal times. The square of the period of revolution of a planet is proportional to the cube of its average distance from the Sun. During this same period the Italian astronomer and natural philosopher Galileo Galilei made progress in understanding “natural” motion and simple accelerated motion for earthly objects. He realized that bodies that are uninfluenced by forces continue indefinitely to move and that force is necessary to change motion, not to maintain constant motion. In studying how objects fall toward Earth, Galileo discovered that the motion is one of constant acceleration . He demonstrated that the distance a falling body travels from rest in this way varies as the square of the time. As noted above, the acceleration due to gravity at the surface of Earth is about 9.8 meters per second per second. Galileo was also the first to show by experiment that bodies fall with the same acceleration whatever thei