Weight is a measurement of the force on a
object caused by gravity trying to pull the object down. Mars has less
gravity than Earth. Therefore if you were on Mars you'd weigh less because the force
of gravity wouldn't be as strong as it is here on Earth.
Does this mean you would suddenly be thinner on
Mars? No. You would have the same amount of mass as you do on Earth. (Mass is
the amount of stuff inside an object.)
So, on Mars, your mass would be the same as it is
here on Earth. But you'd weigh less because Mars has less gravity than Earth.
Gravity is an attractive force. This doesn't
mean it's pretty. What "attractive" means is that an object's gravity
pulls other objects toward it. Look at the chart (see below). The Earth's
gravity naturally pulls us, and everything else, toward the center of the
planet, which keeps us from drifting off into space.
The Earth isn't the only thing that has gravity. In
fact, every single object in the universe has gravity. The tables you're
sitting at have gravity. They are pulling you towards them. You have gravity,
and you are pulling the tables towards you. We can't see or feel these things
happening because people and tables have a such a small mass that the effects
of gravity cannot be seen.
Mass is the amount of stuff contained inside
an object. It takes a lot of mass to make a lot of gravity. The Earth has a lot
of mass, so it has a lot of gravity. The moon's gravity is about 1/6 the amount
of the Earth's because the moon has less mass than the Earth.
So what does all this have to do with weight?
Well, weight is the force on a object caused by gravity trying to pull
the object down. A scale measures how much gravity your mass has. A person
with more mass has more gravity, and therefore weighs more.
You've probably seen video footage of astronauts
walking on the moon. They seem to float between each step. Remember that the
moon has about 1/6 the amount of gravity that the Earth has? Well, if you went
to the moon, you'd weigh less than you do here on Earth. Does this mean you
would suddenly be thinner on the moon? Absolutely not. Your mass would be the
same -- there is no less of you on the moon. But your weight is different
because the moon's gravity is different.