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Earth & Space Science

You will be presented with a series of challenges in which you manipulate variables that affect the motion of planets and moons.

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After completing this tutorial, you will be able to complete the following:

- Explain that gravitational force is the attractive force between masses.
- Explain that the gravitational force between objects with larger masses is greater than the gravitational force between objects with smaller masses.
- Explain that as the distance between objects decreases, the gravitational force between them increases.

Gravitation may be defined as the attractive force between two bodies which is directly proportional to their masses and indirectly proportional to the distance between them. Scientist and mathematician, Sir Isaac Newton, published Principia in 1687 in which he hypothesized the Inverse-Square Law of Universal Gravitation. He used the following equation to express the gravitational force between two objects and the distance between them: force of gravity = where G is the universal gravitational constant. The value of G is approximately Newton's theory of gravitation was used to predict the location in the night sky of Neptune based on the motions of Uranus. We have not yet visited other planets or the Sun, but we know their masses. We calculate their masses by applying Newton's law of gravitation to the measured characteristics of the orbits. However, a discrepancy in Mercury's orbit that could not be accounted for using Newton's theory helped to point out flaws in the theory by the end of the nineteenth century. Although Newton's theory has been superseded, it is still utilized for most non-relativistic gravitational calculations and gives suitably accurate results in most applications.

The discrepancy in Mercury's orbit was accounted for in 1915 by Albert Einstein's General Theory of Relativity. Einstein proposed that the effects of gravitation are ascribed to the curvature or warping of the fabric of spacetime. Spacetime is curved by matter, and the degree of curvature or warping is proportional to the mass of the matter. Einstein's General Theory of Relativity has become a fundamental tool in modern astrophysics and provides the underpinning for the current understanding of black holes. Einstein's General Theory of Relativity is not the only relativistic theory. It is, however, the simplest of its kind and is most consistent with experimental data. Several decades after its discovery, scientists realized that general relativity is incompatible with quantum mechanics. Many hope to reconcile any inconsistencies with a Theory of Everything, hypothesizing that 10-26 spacetime dimensions exist.

Clearly, there is much that scientists do not know yet regarding gravitation and celestial objects. We do know, however that gravitational force is the attractive force between two masses. We have observed that objects that have a bigger mass produce a stronger gravitational pull than smaller ones. Additionally, as the distance between objects decreases, the gravitational force between them increases.

Approximate Time | 30 Minutes |

Pre-requisite Concepts | Learners should be familiar with gravity, mass, motion, orbits, and velocity. |

Course | Earth & Space Science |

Type of Tutorial | Concept Development |

Key Vocabulary | celestial, direction, distance |