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Physics Force Gravity

Overview of the Force of GravityGravity is a term used for gravitation for objects relatively close to Earth. Gravitation is the force that attracts bodies of matter toward each other, often at great distances. Gravity is the force that pulls objects toward the Earth. 


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The equation for the force of gravity is F = mg. The major result of this force is that all objects fall at the same rate, regardless of their mass. Gravity on the Moon and on other planets have different values of the acceleration due to gravity, but the effects of the force are similar. 


 Questions you may have include:* What is the gravity equation?* What is the most outstanding characteristic of gravity?* What is gravity elsewhere?Gravity equationAccording to Newton's Law of Universal Gravitation, gravitation is the force that attracts objects toward each other. 


The equation for that force is:F = GMm/R2For objects relatively close to the Earth, the equation reduces to:F = mgwhere* F is the force pulling objects toward the Earth* m is the mass of the object* g is the acceleration due to gravity; this number is a constant for all masses of matter* mg is the product of m times g(To verify that F = GMm/R2 = mg for objects close to Earth, see Gravity Equation Comes From Universal Gravitation Equation.)


 The gravitation for objects close to the Earth is called gravity. Once an object gets into outer space, the gravitation equation takes over.Acceleration due to gravityThe acceleration due to the force of gravity on Earth is g:g = 9.8 m/s2 in the metric or SI system of measurementg = 32 ft/s2 in the English system of measurementIn the equation F = mg, you must use the same measurement system for mass, m, as you do for g. 


WeightThe weight of an object is the measurement of the force of gravity on that object. You weigh something on a scale, according to the force that the Earth pulls it down:w = mgwhere w is the weight in newtons (N) or pounds (lb).The weight of 1 kg of mass is w = 9.8 newtons.Objects fall at the same rateThe most outstanding characteristic of gravity is the fact that all objects fall at the same rate—assuming the effect of air resistance is negligible. 


This is because the acceleration due to gravity, g, is a constant for all objects, no matter what their mass.This seems counterintuitive, since you would expect a heavy object to fall faster than an object that weighed less. But it is a fact. Try dropping two objects at the same time, from the same height, making sure they are heavy enough not to be affected by air resistance. You will see they hit the ground at the same time.Gravity elsewhereWhen you talk about gravity, you mean gravitation near the Earth. However, the same gravity equation holds for objects near the Moon or other planets, except that the value of g is different. 


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In those cases, you typically tell where the gravity is, such as "gravity on the Moon" or "gravity on Mars."Gravity on the MoonThe force of gravity on the Moon is approximately 1/6 of that on the Earth for a given mass. Thus:Fm = mgmwhere* Fm is the force or weight on the Moon* m is the mass of an object* gm is the acceleration due to gravity on the MoonThe value for gm is 1.6 m/s2 or 5.3 ft/s2. That is approximately 1/6 of the value for g on Earth. Thus, an object on the Moon would weigh about 1/6 of its weight on Earth.Weight on the MoonIf you weight 60 kg (132 pounds) on the Earth, you would weight only 10 kg (22 lbs) on the Moon. 


Dropped objectsIf you dropped two objects of different weights on the Moon, they would fall to the ground at the same rate. You wouldn't have to worry about the effect of air resistance, since there is no air on the Moon.Since gm = g/6, the objects would fall at a slower rate.