Fg is an abbreviation used in physics and engineering for the force exerted by gravity on an object, normally represented in units such as the newton. Fg is always a conservative force.
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Gravity on earth
On Earth, Fg is equal to the mass of an object (in kilograms) times the acceleration caused by gravity, which is approximately 9.8 meters per second squared. This is represented by the formula:
- <math>\mathbf{F}_{g} = m g</math>
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General cases
Between two objects
The force of gravity between two objects of masses m1 and m2 is described by the formula known as the law of universal gravitation:
- <math>\mathbf{F}_{g} = -G \frac{m_1 m_2}{r^3}\mathbf{r}</math>
where r is the position vector between the two objects and r is its magnitude (distance between the objects). G is the gravitation constant
Between many objects
In the more general case, the force of gravity exerted on an object of mass m from N objects is equal to the vector sum of all the individual, given by the equation:
- <math>\mathbf{F}_{g} = \sum_{i=1}^{N} -G \frac{m m_i}{r_{i}^3}\mathbf{r}_{i}</math>
