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Gravitational field
Date: Dec. 1, 2014
From: World of Physics
Publisher: Gale
Document Type: Topic overview
Length: 536 words
Content Level: (Level 4)
Lexile Measure: 1200L
Full Text:
The gravitational field is a measure of the gravitational force present in a region of space due to material objects. A quantitative
description of the gravitational field is developed in the following way: take the force felt by a test body and divide it by its own mass.
The test body may be moved from place to place to map out the size of the field. This equation is Newton's law of universal
gravitation extended to a many-particle (or n-particle) system. Although Newton's law of gravitation is applicable in many instances,
it is not applicable when relativity (special or general) must be taken into account.
The gravitational field, represented by the symbol g, is defined as the gravitational force per unit mass. For any object whose mass is
constant, Newton's second law of motion states that the net external force (F) on a body is the product of the body's mass (m) and
acceleration (a), or F = ma. Dividing both sides of this equation by the mass m yields the equation a = F/m. This equation shows that
the gravitational field g is itself a type of acceleration. Specifically, it is the acceleration of the test mass m0 due to gravity. Near
Earth's surface, the value of g is approximately 9.8 m/s2 (32 ft/s2).
Within the past half-century, many discoveries have been made concerning the solar system's planets, planetary moons, asteroids,
and other bodies. For some of these celestial bodies, gravity maps have been constructed. The gravity map of a celestial body is the
primary method for determining the mass distribution within that body. For example, the Magellan probe sent to the planet Venus in
1989 was used not only to map its surface with the use of radar, but to create a gravity map of the planet as well. By recording the
velocity and position of the Magellan probe as it orbited Venus, information about the gravitational force exerted on Magellan due to
Venus was calculated. Dividing the gravitational force F by Magellan's mass at numerous points yielded the gravitational field just
above Venus's atmosphere.
The gravitational field is useful in addressing the so-called "action-at-a-distance" problem. In fact, this was a criticism leveled at
Newton's law of universal gravitation concerning the mechanism through which material bodies attract one another. A spring or lever
through which forces are applied to various objects can be touched and held in one's hands. In contrast, the notion of all objects in
the universe attracting one another through an invisible, permeating force seemed to some people during Newton's lifetime as being
on the level of black magic. Isaac Newton was aware of this problem, but he was unable to satisfactorily resolve it. The development
of the gravitational field concept allowed people to think of the field itself as acting upon the masses present in a region of space. The
gravitational field lines can be thought of as permeating a region of space so that when an object is brought into this space, it is
affected by (and interacts with) these lines. However, the action-at-a-distance problem was not completely remedied until the
development of relativity theory in the twentieth century.
Source Citation (MLA 9th Edition)
"Gravitational field." World of Physics, Gale, 2001. Gale In Context: Science,
link.gale.com/apps/doc/CV2434500209/SCIC?u=ko_k12hs_d68&sid=bookmark-SCIC&xid=fb86deb8. Accessed 1 Jan. 2022.
Gale Document Number: GALE|CV2434500209