Mass != Weight

On the off chance that anyone who works at the National Air and Space Museum reads this, take heed:

The kilogram is a unit of mass. The pound is a unit of weight. Weight is the gravitational force exerted on an object. Mass is not affected by gravitational fields (barring relativistic effects, at least).

A kilogram weighs 2.2 pounds on Earth, and weighs one-sixth that on the moon. That does not mean that an object’s mass also decreases by a factor of six when you put it on the moon. If you really want to talk about the weight of the stuff sent up on the Apollo missions, start using newtons as your metric measurement instead of kilograms.

And people wonder why the probes we send to Mars go off course.

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