Ask A Scientist General Science Archive

name         libby
status       other
age          11

Question -   What would happen to your weight if you went on the moon?
Why does this happen?
----------------------------
 
Libby,
 
Weight is what you get when you stand on a scale. Scales are weight measuring devices that 
use a spring or some kind of metal bar that stretches or bends when your weight is applied 
to it. The heavier you are, the greater the amount of stretch or bend. That flexing is 
transferred to the dial of the scale so you can read your weight.
 
The moon is much smaller than the earth. As a result, the force of gravity on the moon is 
only about one sixth as strong as gravity on earth. Gravity is what holds us down on the 
earth's (or moon's) surface.
 
If you were to weigh yourself on a scale here on earth and then could take that same scale 
to the moon and weigh yourself there, the weight read on the moon would be 1/6 your earth 
weight. So, If you weighed 100 pounds on earth, you would weigh only about 16 pounds on the 
moon.
 
Regards,
ProfHoff 840
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You have a certain mass.  Mass is how much stuff you are made of, and it is
the same whether you are on Earth, on the moon, on Mercury, or anywhere else
you can think of.  You are held on Earth by gravity.  Gravity pulling on your
mass is your weight (you will learn in school about gravity as a force, if
you have not already).  The amount gravity pulls on you anywhere depends on
your mass and the mass of the other object (and how far apart the objects
are). The moon is smaller than Earth and has a smaller mass, so the moon
won't pull on you as much if you are standing on it.  The moon's gravity is
about 1/6 that of Earth's gravity.  If you weigh 60 pounds on Earth, fly to
the moon with a scale and stand on it, you will weigh about 10 pounds.  If
you weigh 120 pounds on Earth, you will weigh about 20 pounds on the moon. If
you want to figure out how much YOU would weigh on the moon, take YOUR weight
and divide it by 6.

Pat Rowe
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Libby -

Weight is caused by the mass of two objects that are near each other.  The
bigger the objects, the more the force of gravity.  (And gravity is what
causes weight.)  If you weigh 100 pounds on the earth, you would weigh more
on a larger planet... like Jupiter where you would weigh about 236 pounds.

On the moon, because the moon is much smaller than the earth (but remember,
you are the same size) you would weigh about 17 pounds.  Think what a great
high jumper you could be!  However, in order to survive on the moon you
would need a survival suit that could weigh as much as 300 earth pounds...
or about 50 pounds more on the moon.  Even with that, you and your suit
would only weigh about 67 pounds.  That is lighter than you are as you sit
reading this note.

Have you seen movies of men walking on the moon?  Do they appear to be
lighter?  They are.  More than that, because the moon has less mass (and
therefore less gravitational force) when something falls, it falls more
slowly.

Are you ready for the trip to the moon.  I have been for a long time.  More
than that, it seems there is an interest in returning there.  Let's go!

Larry Krengel

P. S. If you want to calculate your weight in other parts of the solar
system, you can at this web site -

www.exploratorium.edu/ronh/weight/index.html

LK
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Hello Libby!

Before we get into answering your question, there are 2
important definitions that need to be brought into the
conversation.  These include the definitions of weight and
mass.  All too often these terms are used interchangeably,
which drives most scientists up a tree!  

Mass is the amount of matter (material) that makes up an
object.  The tricky definition of mass deals with inertia,
which is probably a bit beyond where you are at in science
class.  Technically mass is a measure of how much inertia
an object displays - but if that confuses you don't worry
about it for now. :)  The important thing to remember about
mass is that it is constant, and therefore if you are on
Earth, the Moon, Mars, or anywhere, your mass is always
going to be the same.  

Weight is defined as the product of a body's mass and the
gravitational acceleration in which the mass is located.
 (Weight = Mass x Gravity) What this means is that your
weight depends on both your mass (which doesn't change) and
the gravitation force of the place you are located.
 Therefore, a place with less gravity would cause an object
to have less weight.  So on the moon, where there is less
gravity, you would weight less than you do on Earth where
there is more gravity.  (Have you ever seen a video of a
Moon walk?  The astronauts, when they step they look like
they are bounce around?  That's because there is so much
less gravity on the Moon.  It looks funny because we are
use to seeing people walk on Earth where there is more
gravity).

Let's look at an example, but we'll use the metric
measuring system because it is the best measuring system to
use in science.

Let's say we have a 1kg object (a kilogram (kg) is a
measure of mass).  The value of gravitational acceleration
on Earth = 9.8m/s^2.  On the moon, gravitation acceleration
is 1.67 m/sec^2.  So how much does that object weight on
the Earth verses the Moon? 

Earth
1kg X 9.8m/s^2 = 9.8 Newtons

Moon
1kg X 1.67m/s^2 = 1.67 Newtons

Although the units used in this calculation may look
confusing (in a few years you'll be a wiz at the metric
system), you can nonetheless see that on the Moon a 1kg
object weighs MUCH LESS than it does on the Earth!

Now, isn't that much better than any diet you've ever heard
of!  Anyone feeling the need to lose weight simply needs to
be sent to the moon ;)  hehehe . . . I crack myself up.

I hope that helps, and good luck!
Susannah Sample
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Your weight would be 1/6th of what it is on the Earth.
This is because the mass of the Moon is 1/6th that of the Earth.

Howard Barnes.
=====================================================
Hi Libby,

Weight is actually the measure of gravity pulling on you.  On Earth, the
Earth pulls on you, and you pull on it.  The amount of gravity is determined
by the size of the two objects pulling on each other.  The moon is about 1/6
as big as the Earth.  So it pulls on you with about 1/6 the force.  So if
you could go to the moon, you would weigh about 1/6 of what you weigh on
Earth.  Weird isn't it?!  Now lets say you get to travel to Jupiter.
Jupiter is A LOT bigger than the Earth, so you weigh a lot more because
Jupiter would be pulling on you with a greater force.

One more weird thing to think about.  You wouldn't get skinnier by going to
the moon, or fatter by going to Jupiter.  The amount of stuff that makes you
up would still all be there.  That's called you mass.  Mass never changes.
Weight changes depending on where you are in the universe.  Your weight
actually changes a teeny bit here on Earth if you are on the top of a very
high mountain compared with your weight at sea level.

I hope this explains a little.  There might be some books in the library
that would be helpful.  Ask your friendly librarian.  Good question.

Happy Science!

Martha Croll
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>     The unexplained answer is almost exactly 1/6. But how that happens is
more important. Isaac Newton discovered the "universal" law of gravity. At
the time, and even today, this law of gravity confuses some people because
they confuse MASS and WEIGHT. The MASS of an object is the quantity of
matter it possesses. You can ask, "How do we know what that is?" But the
answer to that question is too complex to go into here. Just assume that
every object contains a quantity of matter, and that quantity is called its
mass. Give it the symbol 'M'.
    The WEIGHT of an object is the force exerted upon it by all other
objects in the WHOLE UNIVERSE!! Give that mass the symbol 'm'.
    Fortunately, only a few and usually only 1 or 2 objects are close enough
to have their effect important. In our case only the Earth, Moon, and Sun
are important. If we never left the surface of the Earth, the distinction
between MASS and WEIGHT could be used interchangeably, but they are
different. If you have ever ridden on a roller coaster, and felt like you
were being "squeezed" into your seat, or you were "floating" you experienced
the difference in your WEIGHT even though your MASS remained the same.
    Isaac Newton discovered the formula that connects the WEIGHT, the MASS,
and the DISTANCE separating two objects. The formula is: W = G * M * m /
R^2.
In his formula: W is the WEIGHT of the object, M is its MASS, m is the MASS
of the other body, R is the distance that separates the two and G is a
universal constant. G = 6.67259x10^-11 (m^3*kg^-1*sec^-2) but you don't need
this to answer your question, as you will see.
    Standing on the Earth your WEIGHT depends upon your mass, M, the mass of
the earth, m, that remains fixed, and R, how far you are from the center of
the Earth. The reason people confuse WEIGHT and MASS is because, so long as
you remain stationary everything in the formula W= G * M *m / R^2 stays the
same so it doesn't make any difference if you use M or W in comparing two
objects.
    Now back to your Moon question. The ratio of your weight on the Moon,
Wmoon, compared to your weight on the Earth, Wearth is:
Wmoon / Wearth = G * M * m(moon) / (Rmoon)^2 / G * M * m(earth) /
(Rearth)^2. This simplifies by cancellation to: Wmoon / Wearth = m(moon) /
(Rmoon)^2 /  m(earth) / (Rearth)^2. Notice that the ratio of your weight
doesn't even depend upon how much or how little your mass is. The quantities
you need then, are:
m(moon) = 7.35x10^22 kg, m(earth) = 5.9743x10^24 kg, Rmoon = 1.738x10^6
meters,
Rearth = 6.378x10^6 meters.
    So, plugging these numbers in you find that: Wmoon / Wearth = 0.1668 and
1/6 = 0.1667 Hmmm! Is this a coincidence, or is there some underlying
principle??
    There are a couple of other interesting facts. The local force of
gravity, that is the apparent weight of a known mass varies from place to
place on the Earth (and other astronomical bodies too) depending upon
whether you are on a mountain or in a valley and whether you are standing on
dense rock or loose sand. There are instruments that can measure this
difference. The most sensitive are pairs of satellites orbiting the Earth
that compare their position as the pass over the same spot on the Earth at
different times. Using these instruments, scientists are making detailed
gravitational "maps" of the Earth.
    If you would like to know how much you would weigh on other planets,
find the site:
http://kids.msfc.nasa.gov/Puzzles/Weight.asp and plug in your weight.

Vince Calder
=====================================================
Libby,

The gravitational attraction at the lunar surface is one-sixth of that experienced on Earth's 
surface ( a 100-pound person on Earth weighs only 17 pounds on the Moon).  This difference 
allows an astronaut to lift a "heavy" life-support system with relative ease.  If it were not 
necessary to carry such a load, an astronaut could jump six times higher on the Moon than on 
Earth. I hope that this helps answer you question.

Sincerely,

Bob Trach
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