Browse Definitions :
Definition

# gravity (or gravitation)

Gravity, also called gravitation, is a force that exists among all material objects in the universe. For any two objects or particles having nonzero mass, the force of gravity tends to attract them toward each other. Gravity operates on objects of all sizes, from subatomic particles to clusters of galaxies. It also operates over all distances, no matter how small or great.

Gravitation is one of the most studied phenomena in physics. Isaac Newton defined its behavior with his famous Law of Universal Gravitation. Newton hypothesized that the force of gravity between any two spherical objects of uniform density is directly proportional to the product of their masses, and inversely proportional to the square of the distance between their centers. According to this law, if m1 and m2 are the masses of two objects, and if their centers are separated by a distance d, then the gravitational force (f) between them is given is given by the following formula:

f = km1m2/d2

where k is a constant that depends on the units specified for m1, m2, d, and f.

Newton's theories about gravitation were modified in the 20th century when Albert Einstein developed the general theory of relativity. Einstein saw that the nature of the force of gravity is the same as the nature of the force exerted on any object that undergoes acceleration. This is known as the Principle of Equivalence. He also demonstrated mathematically that gravitational fields cause distortion in space and time. These hypotheses have been validated by experimentation.

Every object in the universe is surrounded by a gravitational field. The strength of the field is directly proportional to the mass of the object, and inversely proportional to the square of the distance from its center (for any point outside the object itself). Thus, the gravitational field of the sun is stronger overall than that of the earth, and the gravitational field of the earth is stronger in the vicinity of a person standing on the surface than it is at the altitude of a satellite in orbit. Nevertheless, the gravitational field surrounding any object extends indefinitely in all directions. Every particle in the entire universe is gravitationally attracted to every other particle. This is an important consideration in the development of theories concerning how the universe formed, how it is evolving, and what fate ultimately awaits it.

Long thought to exist before they were detected, gravity waves were first hypothesized in Einstein's general theory of relativity, which predicted that an accelerating mass would radiate gravitational waves as it lost energy. On February 11, 2016, David Reitze, executive director of LIGO (Laser Interferometer Gravitational-Wave Observatory) reported that researchers had detected gravitational waves. Reitze said the waves were created by the merging of two black holes, one of which had the mass of 29 suns and the other 36. The discovery is expected to yield a vast amount of information about the universe and the matter and energy within it and to also lead to a great number of practical applications.

This was last updated in February 2016

• User Datagram Protocol (UDP)

User Datagram Protocol (UDP) is a communications protocol primarily used to establish low-latency and loss-tolerating connections...

• Telnet

Telnet is a network protocol used to virtually access a computer and provide a two-way, collaborative and text-based ...

• big-endian and little-endian

The term endianness describes the order in which computer memory stores a sequence of bytes.

An advanced persistent threat (APT) is a prolonged and targeted cyber attack in which an intruder gains access to a network and ...

• Mitre ATT&CK framework

The Mitre ATT&CK (pronounced miter attack) framework is a free, globally accessible knowledge base that describes the latest ...

• timing attack

A timing attack is a type of side-channel attack that exploits the amount of time a computer process runs to gain knowledge about...

• employee resource group (ERG)

An employee resource group is a workplace club or more formally realized affinity group organized around a shared interest or ...

• employee training and development

Employee training and development is a set of activities and programs designed to enhance the knowledge, skills and abilities of ...

• employee sentiment analysis

Employee sentiment analysis is the use of natural language processing and other AI techniques to automatically analyze employee ...

• customer profiling

Customer profiling is the detailed and systematic process of constructing a clear portrait of a company's ideal customer by ...

• customer insight (consumer insight)

Customer insight, also known as consumer insight, is the understanding and interpretation of customer data, behaviors and ...