Gravity And The Earth

A ball drops to the ground. Leaves fall from a tree. Gravity is at work all around you. But what exactly is gravity? And how does it affect different objects? Read this book to find out! Learn all about matter, energy, and forces in the Exploring Physical Science series—part of the Lightning Bolt BooksTM collection. With high-energy designs, exciting photos, and fun text, Lightning Bolt BooksTM bring nonfiction topics to life!

The author of this history of mankind’s increasingly successful attempts to understand, to measure and to map the Earth’s gravity field (commonly known as ‘little g’ or just ‘g’) has been following in the footsteps of the pioneers, intermittently and with a variety of objectives, for more than fifty years. It is a story that begins with Galileo’s early experiments with pendulums and falling bodies, progresses through the conflicts between Hooke and Newton and culminates in the measurements that are now being made from aircraft and satellites. The spectacular increases in accuracy that have been achieved during this period provide the context, but the main focus is on the people, many of whom were notable eccentrics. Also covered are the reasons WHY these people thought their measurements would be useful, with emphasis in the later chapters on the place of ‘g’ in today’s applied geology, and on the ways in which it is providing new and spectacular visions of our planet. It is also, in part, a personal memoir that explores the parallels between the way fieldwork is being done now and the difficulties that accompanied its execution in the past. Selected topics in the mathematics of ‘g’ are discussed in a series of short Codas.

The Earth's Shape and Gravity focuses on the progress of the use of geophysical methods in investigating the interior of the earth and its shape. The publication first offers information on gravity, geophysics, geodesy, and geology and gravity measurements. Discussions focus on gravity measurements and reductions, potential and equipotential surfaces, absolute and relative measurements, and gravity networks. The text then elaborates on the shape of the sea-level surface and reduction of gravity observations. The text takes a look at gravity anomalies and structures in the earth's crust; interpretation of gravity anomalies; and gravity anomalies and the interior of the earth. Topics include general principle; direct and indirect methods; low order harmonics in the gravitational field; rock densities; ocean trenches; and sedimentary basins. The book then examines the place of gravity measurements in geophysical prospecting and tidal variations of gravity. The manuscript is a dependable source of information for readers interested in the shape and gravity of the earth.

Volume resulting from an ISSI Workshop, 11-15 March 2002, Bern, Switzerland

These Proceedings include the written version of papers presented at the IAG International Symposium on "Gravity, Geoid and Earth Observation 2008". The Symposium was held in Chania, Crete, Greece, 23-27 June 2008 and organized by the Laboratory of Geodesy and Geomatics Engineering, Technical University of Crete, Greece. The meeting was arranged by the International Association of Geodesy and in particular by the IAG Commission 2: Gravity Field. The symposium aimed at bringing together geodesists and geophysicists working in the general areas of gravity, geoid, geodynamics and Earth observation. Besides covering the traditional research areas, special attention was paid to the use of geodetic methods for: Earth observation, environmental monitoring, Global Geodetic Observing System (GGOS), Earth Gravity Models (e.g., EGM08), geodynamics studies, dedicated gravity satellite missions (i.e., GOCE), airborne gravity surveys, Geodesy and geodynamics in polar regions, and the integration of geodetic and geophysical information.

Gravity interpretation involves inversion of data into models, but it is more. Gravity interpretation is used in a “holistic” sense going beyond “inversion”. Inversion is like optimization within certain a priori assumptions, i.e., all anticipated models lie in a limited domain of the a priori errors. No source should exist outside the anticipated model volume, but that is never literally true. Interpretation goes beyond by taking “outside” possibilities into account in the widest sense. Any neglected possibility carries the danger of seriously affecting the interpretation. Gravity interpretation pertains to wider questions such as the shape of the Earth, the nature of the continental and oceanic crust, isostasy, forces and stresses, geol- ical structure, nding useful resources, climate change, etc. Interpretation is often used synonymously with modelling and inversion of observations toward models. Interpretation places the inversion results into the wider geological or economic context and into the framework of science and humanity. Models play a central role in science. They are images of phenomena of the physical world, for example, scale images or metaphors, enabling the human mind to describe observations and re- tionships by abstract mathematical means. Models served orientation and survival in a complex, partly invisible physical and social environment.