G is a symbol used in equations relating to gravitation. Capital G represents a number called Newton’s constant or the gravitational constant. Lower-case g represents the acceleration due to gravity at Earth’s surface.
Newton’s constant is often written with a subscript N, thus: G N. This expression occurs in the equation for Newton’s law of gravitation: F = G N m 1 m 2 ÷ d 2. This equation says that the gravitational force (F) between two objects is equal to G N times the product of the masses of the objects (m 1 and m 2) divided by the square of the distance between the objects (d 2). An object’s mass is its amount of matter; the square of a number is that number multiplied by itself.
Scientists generally use metric terms in applying the equation. Force is given in newtons, masses in kilograms, and distance in meters, with G N = 6.67 × 10–11 newton meter squared per kilogram squared. If the value of G N were written out, there would be a decimal point and 10 zeros in front of the first 6.
Newton’s law is named for its discoverer, the English scientist Isaac Newton. The law was published in 1687.
The symbol g occurs in equations relating to the velocity of an object that is falling near Earth’s surface. The velocity of an object is its speed in a particular direction. In this case, the object is falling toward Earth’s center.
One equation that contains g is v = gt, where v is the velocity of a falling object and t is the time during which the object has been falling. The value of g is different at different places on Earth’s surface; a typical value is 9.8 meters per second squared. The equation does not account for other factors, such as air resistance, that influence the velocity of falling objects.
See also Falling bodies, Law of ; Force ; Gravitation .
