How is it the weight of a planet determined?

Question

How is it the weight of a planet determined?

Answer 1

Hello!

As the acceleration of gravity cannot be measured on other planets (except the rocky interior planets), we cannot find the mass of them, by depending on Newton's law of gravity. That's why we use other methods.
The most common way to calculate the mass of a planet is by the moment of Inertia. I=S[r^2(m)dm], (S=integral) r=distance from the axis rotation, m=mass.
It is easy to find the moment of Inertia from the torque of the body: N=I*a, where
a=angular acceleration=dω/dt (first derivative of angular velocity).
Measurement of the acceleration of gravity is made with Gravimeters, very high tech instruments (space technology).
In astrophysics and geophysics that's how a mass of a planet is calculated.

Answer 2

Simple--you take a table that weighs 10 lbs, put it on the ground, and you have a planet that weighs 10 lbs!

"Weight" is defined as the force BETWEEN 2 OBJECTS that is caused by gravity. It makes no sense to talk about the "weight" of the Earth, because you need something to weigh it against. Whenever we talk about how much something small "weighs," we are actually talking about how much it weighs against the Earth.

What you are really thinking about is "mass." The easiest way to measure a planet's (including the Earth's) mass, is to take an object with known mass on the planet's surface and use the equation:

F = G x m1 x m2 / r^2

Where F is the "weight" between two objects, G is Newton's gravitational constant, m1 is the mass of your test object, and r^2 is the distance to the center of the planet squared. Solving for m2 will give you the mass of the planet.

If you can't actually get to the planet to put a test mass on the ground, you can orbit it with a satellite. Then, use the equation:

m = r x V^2 / G

where m is the mass of the planet, r is the radius of the orbit, V^2 is the speed of the satellite squared and G is Newton's gravitational constant. Note that you don't need to know the mass of the satellite with this setup.

Answer 3

While I don't know if this is the exact way we can determine the weight but here it goes...

Determine the orbit radius and its year length. You can then calculate the gravitational attraction between the two masses.

Additionally, there are moons that rotate the planets and light that bends due to the gravity around these planets.

Sorry its not more specific.

Answer 4

mass determines gravity. not something has weight until gravity pulls on it. so if the earth is greater dense than neptune, yet neptune has greater mass besides, neptune might have a greater gravitational pull. even with the undeniable fact that, a planet's gravitational pull would not make sure the style of moons it has. it somewhat is purely the style of bodies that have been given caught in its orbit. Neptune is on the sting of the photograph voltaic device, so that's greater possibly to run into stuff and pull it in. stuff that gets to earth has to make it previous fairly some different planets and the asteroid belt to get caught in our gravitational pull, plus not get sucked in in direction of the sunlight. that's plenty greater stable for earth to 'capture' a moon.

Answer 5

It is done by taking the estimated average density of known materials present and multiplying by the optically measured volume of the planet.

The size of the planet is determined by triangulation calculations to get the distance from Earth, then measuring the angular sweep from edge to edge to determine the diameter. 4/3*pi*radius^3 gets volume. Volume times average density gives you weight.

The weight can be further cross-checked against the estimates of any sizeable satellites and the "wobble" measured.

Answer 6

I think they determine mass not weight - since weight is gravity dependent.

For mass I am sure they take into average density and size and go from there. With those two numbers you can figure out mass.

Then from there apply conversion stuff to find weight equivalents,

Answer 7

Hi. Weight is mass, mass causes gravity, gravity is a constant called 'g'. The hard part was determining 'g'. They used a torsion scale and found the value, the rest was arithmetic. http://www.stanford.edu/group/kgb/Research/gravity2.html