# Q & A: Weight vs. Mass

Q:
What is the weight of the moon?
- Tatyana (age 40)
Columbia, SC US
A:
Hello Tatyana, you bring up a very interesting question.  For things like the Moon, weight is not a very practical term.  To answer your question, the words weight and mass must first be explored.

Mass is a measure of how much stuff something has.  To illustrate this I'll use an example.  When a car and a dump truck traveling at the same speeds but opposite direction crash, the dump truck always wins: it has more mass.  Weight is the measure of gravity upon a mass.  That is to say, it is the force that gravity exerts on an object.  So if the dump truck was on the Moon and the car was on the Earth then the dump truck would weigh less because Earth's gravitational field is stronger than the Moon's.

Anyway, the Moon has a mass of 7.3477*1022 kilograms.  For a reference aforementioned baseball has a mass of about 0.145 kilograms and the Earth has a mass of 5.9736*1024 kilograms.  So the Earth is about 70 times more massive than the Moon.   Hope this clears things up for you!

Mark

(published on 10/29/2009)