2006-09-05 06:36:51 · 22 answers · asked by jeet 1 in Science & Mathematics ➔ Astronomy & Space
The weight (more properly, the mass) of the Earth and other bodies can be determined from applying the laws of gravity. The mass of the Earth can be determined simply from the force at gravity at its surface. The equation of gravity is F=GMm/r^2, where G is the gravitational constant, M and m are the two masses, and r is the distance between the centers of mass. The key to measuring the mass of the Earth was determining the value of G. This was first done by Henry Cavendish in 1798.
Masses of other bodies can be determined from the orbits of objects around them. In simplified form, you set the force of gravity equal to the centripetal force needed to maintain the orbit (mv^2/r) and solve for M.
2006-09-05 06:53:37 · answer #1 · answered by injanier 7 · 0⤊ 1⤋
Ok, wieght is how heavy something is, its the mass of a planet thats important, so how do we measure the mass of a planet?
first thing we have to do is work out how strong gravity really is, not anything's gravity, but the general value.
we have the equation: weight = Gravity * mass1 * mass2/ distance squared
written f=Gm1m2/r^2
what you do is get 2 masses and measure the force between them (say two 1lb weights near eachother) that way we can get a value for G
once we have G, we can measure the mass of the earth by weighing a known mass right here on the surface.
when you have the mass of the earth and you know its orbit round the sun you can calculate the mass of the sun.
likewise, once you know the mass of the sun you can calculate the mass of any planet that you know the orbit.
2006-09-05 13:50:23 · answer #2 · answered by a tao 4 · 0⤊ 0⤋
The biggest balancing scale you've ever seen!
Actually, the way the mass of a heavenly body is estimated (as we are not sure to an exact degree) is from it's gravitational pull.
We know a body's gravitational pull is directly proprtional to it's mass.
So if we know an object's acceleration towards a body at a certain distance, we can ascertain that body's mass.
This stems from the equation for gravitational force of a body,
F = GMm/r^2 ...
or,
a = GM/r^2 ... Thus a body's mass is given by,
M = a*r^2/G
This one of the way we estimate mass. There are other much more accurate methods, however, this is the one that is simplest to explain and understand.
2006-09-05 14:41:16 · answer #3 · answered by AresIV 4 · 0⤊ 1⤋
The measurement is based on the gravitational effects caused by the sun, its distance from the planet in question, and the overall mass of the planet. From there you can approximate the effects of those forces in a matter of weight put upon you body by all of the force being applied to your body. ( Depending on which measure you use the may account for the atmosphere as well. This is determined by spectral analysis of the light being returned to ground and satellite based telescopes.)
2006-09-05 13:47:06 · answer #4 · answered by Super Sean 3 · 0⤊ 1⤋
It's more accurate to talk about their "mass". Weight depends on the local gravitional field.
One way to estimate the weight is through their gravitational effects, by the orbits of their satellites or the drag and pull on other planets.
2006-09-05 13:40:20 · answer #5 · answered by Zhimbo 4 · 0⤊ 0⤋
Obviously, they are not directly weighed. The volume is determined, then mass is calculated based on average density of the object.
Mass can also be determined by the gravitational influence that a body has on a nearby body of known mass.
For distant stars, the size relative to the Sun is determined based on luminosity, X-ray emmisions, etc., then a mass is determined.
2006-09-05 13:42:10 · answer #6 · answered by Duluth06ChE 3 · 0⤊ 2⤋
Going to basics...Weight is based on the gravitational pull of a mass like Earth and another mass like me. Mass and weight are two different things. Weight is referred to when you have gravitationa pull. Mass is just how much matter is in it.
The weight of planets are educated estimates based on known and theorized things. For example, we can estimate how much water there is on Earth and calculate its weight. However, no one knows what is in the center of the Earth, so it is just a guess. All weights are only estimations of what we believe to be there and that includes all planets.
2006-09-05 13:56:31 · answer #7 · answered by CHEPIBE72 5 · 0⤊ 2⤋
We study about "mass". It is measured by their gravitational affect. g=(GM/square of r). G is a constant. If the radius of the celestial body is known and its acceleration due to gravity, then the mass can be calculated
2006-09-06 10:14:13 · answer #8 · answered by sakura 2 · 0⤊ 0⤋
My guess is that they estimate the weight by the mass and size of the planet. Using this they can probably get a good estimate
2006-09-05 13:42:20 · answer #9 · answered by Judgerz 6 · 0⤊ 1⤋
The planets are weighed by calculating the time it takes to complete their orbits, I don't know exactly how because im not in NASA, but they measure the time of one orbit and something to do with their diameter, Its a bit vague but thats all i know. ^^
2006-09-05 13:44:32 · answer #10 · answered by Phoebe ^^ 1 · 0⤊ 0⤋