WEIGHT

"Weight" is a succinct way of saying "the gravitational force between a planet (or moon or asteroid, or whatever) and a person (or object) standing on that planet (or moon or asteroid, or whatever)". We compute weight using a version of the gravitational formula, with

R₁₂ = the distance between the center of the planet and the center of the person. If the person is standing on the surface of the planet, this is effectively the same as the radius of the planet, R_PL give or take a meter of two...

So the general formula is

As with the generic gravitational formula, we can avoid having to know the value of G by comparing two weights. We can compare someone's weight on Earth to their weight on another planet, or to their weight on an Earth that has had its mass and/or radius changed.

Note that now G and the mass of the person drop out, and we are left with

Or, to look at it another way:

Using the version above, we first calculate the ratio [M_PL / M_E] . Then we compute the ratio [R_PL / R_E] and square it. Then divide one by the other!

In this equation, the units for mass do not matter, so long as they agree. The same goes for the units of distance. We will typically know the value of W_E in pounds.

Sample Calculations

To see some sample calculations with density, click on the examples below

• Example 1
• Example 2

Updated 8/27/99

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