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Conversely, as two massive objects move towards each other, the motion accelerates under gravity causing an increase in the (positive) kinetic energy of the system and, in order to conserve the total sum of energy, the increase of the same amount in the gravitational potential energy of the object is treated as negative.
Anti-gravity is a recurring concept in science fiction. Examples are the gravity blocking substance "Cavorite" in H. G. Wells 's The First Men in the Moon and the Spindizzy machines in James Blish's Cities in Flight .
Bureaucratium is an element with a negative half-life, becoming more massive and sluggish as time goes by. Byzanium Raise the Titanic! [29] Fictional element in the book Raise the Titanic! and its film adaptation, which is a main focus of the story arc. It is a powerful radioactive material sought by both the Americans and Russians for use as ...
The gravitational potential (V) at a location is the gravitational potential energy (U) at that location per unit mass: =, where m is the mass of the object. Potential energy is equal (in magnitude, but negative) to the work done by the gravitational field moving a body to its given position in space from infinity.
The gravitational potential energy is the potential energy an object has because it is within a gravitational field. The magnitude of the force between a point mass, M {\displaystyle M} , and another point mass, m {\displaystyle m} , is given by Newton's law of gravitation : [ 3 ] F = G M m r 2 {\displaystyle F={\frac {GMm}{r^{2}}}}
Black holes, objects whose gravity is so strong that nothing—including light—can escape them, have been depicted in fiction since at least the pulp era of science fiction, before the term black hole was coined. A common portrayal at the time was of black holes as hazards to spacefarers, a motif that has also recurred in later works.
Neutron star mergers, and their potential to cause extinction events at interstellar distances due to the enormous amounts of radiation released, also feature on occasion. Neutronium, the degenerate matter that makes up neutron stars, often turns up as a material existing outside of them in science fiction; in reality, it would likely not be ...
The product GM is the standard gravitational parameter and is often known to higher precision than G or M separately. The potential has units of energy per mass, e.g., J/kg in the MKS system. By convention, it is always negative where it is defined, and as x tends to infinity, it approaches zero.