Source: GodfreyKneller-IsaacNewton-1689, Godfrey Kneller, Wikimedia

The equation that is used to calculate the strength of the gravitational attraction between two objects was developed by Sir Isaac Newton. For more information, scroll over the variables in the equation.

Note: The negative sign in the equation is there because gravity is always an attractive force—it always pulls masses closer together. When solving a problem, you can leave the negative sign out, and answer with a phrase such as, "An attractive force of _________N"

Gravitational Force Sample Problem:

Calculate the gravitational attraction between your two classmates, one with a mass of 63 kg and another with a mass of 47 kg if they are 2.7 m apart. If you need help, click on the hint or check your answer buttons.

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Need a hint?

G = 6.67 x 10^-11 N•m²/kg²
m₁ = 63 kg
m₂ = 47 kg
Distance between centers of mass = 2.7 m
F_g = ?
F_g = -G m₁m₂ d²

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Check Your Answer

F_g = -G m₁m₂ d² = - 6.67 x 10^-11 63x47 2.7² = - 2.7 x 10^-8 N
There is an attractive force of 2.7 x 10^-8N

Your weight on the Earth depends on othe mass and size of the earth itself, go to this website and enter your weight to see what you would weigh on other planets.
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Answer the following questions in your notes. Why would weight be different on different worlds? What factors cause this difference? Notice the radii of each planet's surface is different, as is its mass.