# Changes

## Wikijunior:Solar System/Uranus/Titania

, 12 years ago
How much would Titania's gravity pull on me?: some bits seemed needlessly confusing for our audience, reword
Nearly half of the moon is made of frozen water. The rest is rock and a mixture of frozen gas.

==How much would Titania'sI gravity pullweigh on meTitania?==

Titania is a small world, but if you weighed 100 pounds or 100 kilograms on Earth, your weight on Titania would be 100 of the same units. If you want to find out exactly how much you would weigh on Titania, just take your weight from Earth, or the doctor's office, and multiply it by 1. Have you learned yet what happens when you multiply any number times one? It just stays the same, doesn't it?
But that's a pretty boring fact. So there must be something more to it&mdash;and there is! Maybe you have visited a science museum where one of the exhibits showed you that your weight would be different on some other planet.

The word ''weight'' is something that we use with several different meanings. Most of the time we use it to measure how much stuff we have. That is the meaning we use when we say that a bag of sugar has a net weighweight of two kilograms or of four pounds. That is also the meaning we use when we weigh ourselves at the doctor's office or at the gym, or when we calculate our Body Mass Index.

But we also sometimes use ''weight'' as a measure of howthe hard something is pressing downward becauseeffects of gravity. Gravity is what pulls us towards the center of the Earth when we are on Earth, or towards the center of Titania if we were on Titania. So, using this sense of ''weight'', we weigh more on Earth than on Titania because Earth's gravity pulls us towards the Earth's center more than Titania would.

The fact that these are slightly different meanings is something which even many grownups have a hard time understanding. Surprisingly, it is often teachers who have problems understanding this. Most teachers who teach younger children don't have too much trouble with this. It is usually the professors who teach science classes to older kids in college who have a hard time understanding this.

If you want to find out exactly how much you would weigh on Titania for this other meaning of weight, you need to use different units. You might just borrow the names of the units we normally use for this purpose, and use the same number here on earth with a new unit that we will call kilograms-force or pounds-force. If we do that, then on Earth the number of these units you weigh in this new meaning of the word ''weight'' is the same as the number of pounds and kilograms you weigh at the doctor's office. But if you go to a different planet or moon, then your weight in pounds or kilograms would stay the same, but your weight in pounds-force or kilograms-force would change. So it doesn't work so well to use the names that are so much alike, if you are not on Earth. In order to keep track of the differences more easily, you can instead use a newer unit that was invented to help keep you from getting confused about these differences.