# gravitational force

### 1.0 Introduction

### 1.1 What is gravitative force?

Gravitational force is defined as a force of attractive force which exerts between two objects with mass. It pulls two objects that have mass. ( Gravitation and Gravity n.d. ) .

### 1.2 Background Information

### 1.2.1 The find of gravitative force

One twenty-four hours, Newton was sitting on his garden and detecting the falling of an apple from a tree. A sudden inspiration appeared in his head. There must be a force exerted on the apple since the apple accelerated while falling down from the tree with zero initial speed. The force is so called “gravity” and the acceleration due to the force is called “acceleration due to gravity” ( Sir Isaac Newton: The Universal Law of Gravitation n.d. ) .

### 1.2.2 Effectss of gravity on planets

If the force of gravitation exerts at the top of the trees and mountains, so it must exercise all the manner to the orbit of the Moon. It is expected that the orbit of the Moon around the Earth consequences from the gravitative force as the acceleration due to the gravitation can alter the speed of the Moon in such a manner it followed an orbit around the Earth ( Sir Isaac Newton: The Universal Law of Gravitation n.d. ) .

### 2.0 The Universal Law of Gravitation

### 2.1 Kepler ‘s jurisprudence of gravity

Kepler ‘s Third Law states that the ratio of the regular hexahedrons of their average distances from the Sun is same as the squares of the periods of any two planets orbit about the Sun.**Phosphorus**represents the clip taken for one revolution about the Sun and**Roentgen**represents the distance between the planet and the Sun. The equation indicates that the period for the planet to revolve the Sun is relative to the radius of its orbit. ( Johannes Kepler: The Law of Planetary Motion n.d. ) . However, the accurate measurings on the orbits of the planets showed that they do non exactly follow Kepler ‘s Torahs. The cogency of the Kepler ‘s jurisprudence is corrected by Newton. The mass of the Sun is highly greater than any other planet. Therefore, the force of attractive force between planets will be little compared to the force due to the Sun ( Sir Isaac Newton: The Universal Law of gravity n.d. ) .

### 2.2 The jurisprudence of cosmopolitan gravity

Law of cosmopolitan gravity provinces that every atom in the universe attracts each another with a force that is relative to the merchandise of their multitudes and reciprocally relative to the distance apart squared. This force exerts along the line of centres fall ining the two atoms. The magnitude of the gravitative force can be calculated utilizing the expression:

**F**_{g}**= GMm F**** _{g}**is the magnitude of the gravitative force

**r? G**is cosmopolitan gravitative invariable

**Meter**and**m**are the multitudes of the two atoms.

**R**is the distance between the two atoms.

The cosmopolitan gravitative force is besides named cosmopolitan changeless as it is expected to be changeless at any times and topographic points. Therefore, it is universally characterized the intrinsic strength of gravitative force ( Sir Isaac Newton: The Universal Law of gravity n.d. ) . The gravitative invariable is really little since we are incognizant of the being of the force of attractive force between objects. The recognized value is G = 6.67 x 10^{-11}Nm?/kg^{2}. Based on the equation, the greater the distance between two multitudes, the smaller the gravitative force ( Universal gravity and weight n.d ) .

### 3.0 Gravitational Fieldss

Gravitational field is defined as the gravitative force felt by a distinct atom in a peculiar country ( Fowler 2006 ) .

### 3.1 Field strength

Gravitational field strength is defined as force,**Nitrogen**per unit mass,**kilogram**. The definition of gravitative field strength is derived from the Newton ‘s 2nd jurisprudence,**?F=ma**. By doing acceleration,**a**, as a topic and so utility acceleration,**a**with gravitative field strength,**g**, and we would obtain a expression,**g = F/m**.**F**represents the gravitative force,**Nitrogen**whereby**m**represents the mass of an object,**kilogram**. Gravitational field strength near to the Earth ‘s surface is the same as the gravitative acceleration, 9.8Nkg^{-1}. When the force is non given, gravitative field strength can be calculated by utilizing the expression,**g = GM/r?**. This expression can be obtained by the permutation of the two equation,**F = milligram**and**F = GMm/r?**. Hence, resulted in the formation of the equation,**g = GM/r?**. The greater the value of**g**, the greater the gravitative field strength ( Universal Gravitation and Weight n.d. ) .

### 3.2 Principle of superposition

In footings of gravity, rule of superposition refers to the entire force of an object. Entire force is the add-on of all the vectors due to the gravitative Fieldss of force moving on the object ( Fowler, 2006 ) . Superposition refers to the multitudes which interact with each other. To happen the entire force, we have to happen the gravitative force for each mass by utilizing the expression, F_{g}= GMm/r? . Finally, add up all the forces by utilizing vector add-on method ( Forces and Fields n.d. ) .

### 4.0 Future of Gravitation

Einstein theorized that gravitation can be explained by the curvature of infinite clip. Space clip is warped by the mass and energy inside of it but non level. Objects travel in consecutive line do non keep by cryptic force but follow the curves in infinite clip. The objects move in consecutive lines along 4-dimensional infinite clip but move in egg-shaped circles in 3-dimensional infinite. Light appears to go in consecutive lines although it is really dead set, curved and changed by the cloth of infinite clip. Although it looks like straight out in forepart of us, it is really around the corner of the Sun because the infinite clip warp morphs the visible radiation. We see merely the consequence of the visible radiation that is being dead set around the Sun. This can non be tested since the Sun is reflecting us right in the eyes and we can non see the stars. However, it is possible to prove out this theory during a entire solar occultation. We are invariably revolving the Sun so we are able to detect the alterations of the motion of the star in orbit ( Space Time: The Fabric of the Universe n.d. ) .

### 5.0 Decision

In decision, based on the acceptable Newton ‘s gravitative jurisprudence of gravity, gravity is a common force. Every atom in the universe attracts every other atom with a force that is straight relative to the merchandise of their multitudes and reciprocally relative to the square of the distance between them. Therefore, gravitative force is depends on the multitudes of the organic structures and the distance between the two organic structures.

### Reference List

*Forces and William claude dukenfields*n.d. , viewed 29 July 2009, hypertext transfer protocol: //electron9.phys.utk.edu/phys136d/modules/m4/efield.htm

Fowler, M 2006*, Gravitational Field*, viewed 29 July 2009, hypertext transfer protocol: //galileo.phys.virginia.edu/classes/152.mf1i.spring02/GravField.htm

*Gravity and Gravity*n.d. , viewed 29 July 2009, hypertext transfer protocol: //alex.edfac.usyd.edu.au/Methods/Science/studentwork/MassoftheEarth/gravitationandgravity.htm

*Johannes Kepler: The Laws of Planetary Motion*n.d. , viewed 29 July 2009, hypertext transfer protocol: //csep10.phys.utk.edu/astr161/lect/history/kepler.html

*Newton ‘s Law of Gravitation*n.d. , viewed 29 July 2009, hypertext transfer protocol: //theory.uwinnipeg.ca/physics/circ/node7.html

*Sir Isaac Newton: The Universal Law of Gravitation*n.d. , viewed 6 June 2009, hypertext transfer protocol: //csep10.phys.utk.edu/astr161/lect/history/newtongrav.html

*Space Time: The Fabric of the Universe*n.d. , viewed 29 July 2009, hypertext transfer protocol: //www.astronomy.pomona.edu/Projects/moderncosmo/alex ‘s % 20page % 201.html

*Universal Gravitation and Weight*n.d. , viewed 29 July 2009, hypertext transfer protocol: //dev.physicslab.org/Document.aspx? doctype=3 & A ; filename=UniversalGravitation_UniversalGravitationWeight.xml