Difference between revisions of "gravity"
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(No latex plugin here, so tidied up a touch. Also fixed sign of F.) |
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| − | ''' | + | '''Gravity''' is the tendency of objects with mass to accelerate toward each other. |
'''Newton's law of universal gravitation''' states the following: | '''Newton's law of universal gravitation''' states the following: | ||
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Every point mass attracts every other point mass by a force directed along the line connecting the two. This force is proportional to the product of the masses and inversely proportional to the square of the distance between them: | Every point mass attracts every other point mass by a force directed along the line connecting the two. This force is proportional to the product of the masses and inversely proportional to the square of the distance between them: | ||
| − | F = G | + | ''F'' = - ''G'' ''M'' ''m'' / '''r'''<sup>2</sup> |
where: | where: | ||
| − | F is the magnitude of the | + | ''F'' is the magnitude of the gravitational force between the two point masses |
| − | G is the gravitational constant | + | ''G'' is the gravitational constant |
| − | + | ''M'' is the mass of the first point mass | |
| − | + | ''m'' is the mass of the second point mass | |
| − | r is the distance between the two point masses | + | '''r''' is the distance between the two point masses |
| − | Assuming SI units, F is measured in | + | Assuming SI units, ''F'' is measured in Newtons (N), ''M'' and ''m'' in kilograms (kg), '''r''' in metres (m), and Newton's gravitational constant ''G'' is approximately equal to 6.67 × 10−11 N m2 kg−2 (Newtons times metres-squared per kilogram-squared). |
| − | It can be seen that the | + | It can be seen that the force ''F'' is always negative. This sign convention is consistent with its electromagnetic equivalent ''Coulomb's Law'', where a positive force means repulsion between two charges. |
[[Category:Glossary]] | [[Category:Glossary]] | ||
{{Stub}} | {{Stub}} | ||
Revision as of 00:44, 14 April 2006
Gravity is the tendency of objects with mass to accelerate toward each other.
Newton's law of universal gravitation states the following:
Every point mass attracts every other point mass by a force directed along the line connecting the two. This force is proportional to the product of the masses and inversely proportional to the square of the distance between them:
F = - G M m / r2
where:
F is the magnitude of the gravitational force between the two point masses G is the gravitational constant M is the mass of the first point mass m is the mass of the second point mass r is the distance between the two point masses
Assuming SI units, F is measured in Newtons (N), M and m in kilograms (kg), r in metres (m), and Newton's gravitational constant G is approximately equal to 6.67 × 10−11 N m2 kg−2 (Newtons times metres-squared per kilogram-squared).
It can be seen that the force F is always negative. This sign convention is consistent with its electromagnetic equivalent Coulomb's Law, where a positive force means repulsion between two charges.