Gravitational energy or gravitational potential energy is the potential energy a massive object has in relation to another massive object due to gravity. It is the potential energy associated with the gravitational field, which is released (converted into kinetic energy) when the objects fall towards each other. Gravitational potential energy increases when two objects are brought further apart.
For two pairwise interacting point particles, the gravitational potential energy U is given by
\( {\displaystyle U=-{\frac {GMm}{R}},} \)
where M and m are the masses of the two particles, R is the distance between them, and G is the gravitational constant.[1]
Close to the Earth's surface, the gravitational field is approximately constant, and the gravitational potential energy of an object reduces to
\( {\displaystyle U=mgh} \)
where m is the object's mass, \( {\displaystyle g=GM_{E}/R_{E}^{2}} \) is the gravity of Earth, and h is the height of the object's center of mass above a chosen reference level.[1]
Newtonian mechanics
In classical mechanics, two or more masses always have a gravitational potential. Conservation of energy requires that this gravitational field energy is always negative, so that it is zero when the objects are infinitely far apart.[2] The gravitational potential energy is the potential energy an object has because it is within a gravitational field.
The force between a point mass, M, and another point mass, m, is given by Newton's law of gravitation: \( {\displaystyle F={\frac {GMm}{r^{2}}}} \)
To get the total work done by an external force to bring point mass m from infinity to the final distance R (for example the radius of Earth) of the two mass points, the force is integrated with respect to displacement:
\( {\displaystyle W=\int _{\infty }^{R}{\frac {GMm}{r^{2}}}dr=} \) \( {\displaystyle -\left.{GMm \over r}\right\vert _{\infty }^{R}} \)
Because \( {\displaystyle \lim _{r\rightarrow \infty }{\frac {1}{r}}=0} \) , the total work done on the object can be written as:[3]
Gravitational Potential Energy
\( {\displaystyle U=-{\frac {GMm}{R}}} \)
General relativity
Main article: Mass in general relativity
A depiction of curved geodesics ("world lines"). According to general relativity, mass distorts spacetime and gravity is a natural consequence of Newton's First Law.
In general relativity gravitational energy is extremely complex, and there is no single agreed upon definition of the concept. It is sometimes modelled via the Landau–Lifshitz pseudotensor[4] that allows retention for the energy-momentum conservation laws of classical mechanics. Addition of the matter stress–energy-momentum tensor to the Landau–Lifshitz pseudotensor results in a combined matter plus gravitational energy pseudotensor that has a vanishing 4-divergence in all frames—ensuring the conservation law. Some people object to this derivation on the grounds that pseudotensors are inappropriate in general relativity, but the divergence of the combined matter plus gravitational energy pseudotensor is a tensor.
See also
Gravitational binding energy
Gravitational potential
Gravitational potential energy storage
References
"Gravitational Potential Energy". hyperphysics.phy-astr.gsu.edu. Retrieved 10 January 2017.
For a demonstration of the negativity of gravitational energy, see Alan Guth, The Inflationary Universe: The Quest for a New Theory of Cosmic Origins (Random House, 1997), ISBN 0-224-04448-6, Appendix A—Gravitational Energy.
Tsokos, K. A. (2010). Physics for the IB Diploma Full Colour (revised ed.). Cambridge University Press. p. 143. ISBN 978-0-521-13821-5. Extract of page 143
Lev Davidovich Landau & Evgeny Mikhailovich Lifshitz, The Classical Theory of Fields, (1951), Pergamon Press, ISBN 7-5062-4256-7
vte
Outline History Index
Fundamental concepts
Energy
Units Conservation of energy Energetics Energy transformation Energy condition Energy transition Energy level Energy system Mass
Negative mass Mass–energy equivalence Power Thermodynamics
Quantum thermodynamics Laws of thermodynamics Thermodynamic system Thermodynamic state Thermodynamic potential Thermodynamic free energy Irreversible process Thermal reservoir Heat transfer Heat capacity Volume (thermodynamics) Thermodynamic equilibrium Thermal equilibrium Thermodynamic temperature Isolated system Entropy Free entropy Entropic force Negentropy Work Exergy Enthalpy
Types
Kinetic Internal Thermal Potential Gravitational Elastic Electric potential energy Mechanical Interatomic potential Electrical Magnetic Ionization Radiant Binding Nuclear binding energy Gravitational binding energy Quantum chromodynamics binding energy Dark Quintessence Phantom Negative Chemical Rest Sound energy Surface energy Vacuum energy Zero-point energy
Energy carriers
Radiation Enthalpy Mechanical wave Sound wave Fuel
fossil fuel Heat
Latent heat Work Electricity Battery Capacitor
Primary energy
Fossil fuel
Coal Petroleum Natural gas Nuclear fuel
Natural uranium Radiant energy Solar Wind Hydropower Marine energy Geothermal Bioenergy Gravitational energy
Energy system
components
Energy engineering Oil refinery Electric power Fossil fuel power station
Cogeneration Integrated gasification combined cycle Nuclear power
Nuclear power plant Radioisotope thermoelectric generator Solar power
Photovoltaic system Concentrated solar power Solar thermal energy
Solar power tower Solar furnace Wind power
Wind farm Airborne wind energy Hydropower
Hydroelectricity Wave farm Tidal power Geothermal power Biomass
Use and
supply
Energy consumption Energy storage World energy consumption Energy security Energy conservation Efficient energy use
Transport Agriculture Renewable energy Sustainable energy Energy policy
Energy development Worldwide energy supply South America USA Mexico Canada Europe Asia Africa Australia
Misc.
Jevons paradox Carbon footprint
Hellenica World - Scientific Library
Retrieved from "http://en.wikipedia.org/"
All text is available under the terms of the GNU Free Documentation License
