How much does the Earth weigh?

[matty2670]

Well, come on then, tell me...

[dawkins]

The earth weighs approx 6 billion trillion metric tons as calculated by Henry Cavendish in 1797

[Loosehead]

5.97x10E24 Kg's

[matty2670]

Wow...
I wasn't expecting that

[shammydodger]

Ah, Henry Cavendish. A man on a different planet to the rest of us.

[scotstone]

The Earth is weightless but has a mass of 5.97 x 10E24kg.

[gen2]

Thank goodness for some Scot's sanity. It is amazing how many people never listened to their science teachers at school and still confuse mass with weight.

I was going to suggest taking the Earth on a trip round the solar system to demonstrate how the weight will change in different places, but came up with two problems:
1) How would you make a big enough spring balance? and
2) Where would you suspend it from?

[JustSia]

Despite the fact that I find it quite irritating also, these terms are acceptably interchangeable in every day life, unless you are a scientist.

[gen2]

Sorry to disagree JustSia, but I would say that these terms are regularly 'confused' in everyday life and that it is ignorance that makes it acceptable to those that don't know anything different.

[JustSia]

Gen2, I know exactly what you�re saying, but at the risk of sounding pedantic, ignorance signifies the lack of knowledge, one can hardly confuse something he/she doesn�t know about. We are all ignorant in one way or another. And to say that the fairly recent distinction between mass and weight (within scientific circles) should automatically be adopted by laymen, whether or not they are aware of kinetics and general relativity, is an unreasonable expectation. Either way, I shall let you be the first one to inform the Weight Watchers of their new name.

[kuhugaq]

Earth's Weight (Mass): 5.972 sextillion (1,000 trillion) metric tons. That's 5,972,000,000,000,000,000,000 tons! Actually, scientists prefer to refer to this measurement as the Earth's mass instead of weight since weight is the result of Earth's gravitational pull on another object. And the Earth cannot pull on itself! As the Earth orbits the Sun, it is weightless. If the Earth were placed on the Sun, it would weigh more than if it were placed on Jupiter, the largest planet in the solar system but much smaller than the sun. Yet, Earth (or any other object for that matter) would have the same mass regardless of where it is located.

[shammydodger]

Ok, so "weight" only applies to terestrial bodies does it?

The Earth isn't weightless. What does the Earth weigh? I don't know. But, at a first guess, I would say it is the mass of the earth multiplied by the acceleration due to gravity. So, approx what Loosehead said, multiplied by 9.81 (in Newtons).

How can something that has mass not have weight?

[kuhugaq]

justificaction

[JustSia]

Shammydodger, my physics knowledge is miniscule, hence not questioning the calculations. Obviously the Earth is not weightless but (this is where I am getting confused) in order to calculate its weight! or gravitational force acting on it shouldn�t you first choose a body against which to do the measuring (i.e. sun). I don�t understand where object acceleration comes into. Isn�t it the straight forward Newton�s calculation or am I confusing it with something else?

F= G*m(Earth)*m(sun) /( r^2)

= [(6.6742 � 0.0010) * 10^-11 Nm^2kg^-2] * (1.9891 * 10^30kg) * (5.9742�10^24kg) / (0.000 016 * 9.460 730 472 580 8�1015 m)^2

= whatever that might be

Please, please, please correct me if I am wrong I am completely lost with it. I am probably making a complete idiot out of myself but hey, if 'you don't ask you don't get'.

[scotstone]

Weight is the measure of the gravitational force of a large mass on a much smaller mass and in the SI system is measured in Newtons. This weight can be calculated by measuring the acceleration of the smaller mass towards the larger mass caused by this gravitational force. On the Earth the acceleration is approximately 9.81m/s2.
From Newton's 2nd law of motion the gravitational force i.e. weight can be calculated from:-

weight(N) = mass (kg) x acceleration(m/s2)

A space satellite orbiting the Earth is considered weightless because the gravitational force exerted by the Earth is cancelled by the centrifugal force due to the orbital speed. For the same reason, as Earth is orbiting the Sun, it is also considered weightless.

Mass is constant irrespective of location whereas weight is dependent on the gravitational pull of a larger mass. For everyday use this distinction is unimportant but in physics and engineering it is necessary to know which to use.

[JustSia]

Now I�m even more confused. I thought that, in the case of the above satellite, the state of weightlessness is due to the free fall and that is generally described by the 1st Newton�s law. It also applies to Earth orbiting the Sun. This is what bothers me, since there is still a gravitational pull the object is not strictly weightless but the existent force is balanced by the orbiting speed giving the appearance of weightlessness, yet the force is still there. Arrrrggggh, now I know why I prefer chemistry, lol.

[mibn2cweus]

The time has come for me to weigh in on this discussion to see if I can incite the wrath of the scientific community:

�Weight� is a context dependent concept with a variety of definitions, thus the confusion. When substituted for the term �mass�, �weight� often becomes a redundant linguistic nightmare.

Mass is substance and weight is force.

The mass of an object is determined by the quality and quantity of the matter of which it is made, independent of gravity. Mass is the weight of an object in a precisely specified force of gravity with no other forces applied. The specific force of gravity that must be used for measuring mass is derived from the force of gravity present at the Earth�s surface but since this force varies for different locations on the Earth�s surface a specific force of gravity has been chosen to serve as a standard for measuring mass.

Conversely, an objects weight is proportional to its mass and the force of gravity that exists at the location at which this measurement is performed rather than a selected standard force of gravity. Weight is gravity dependent.

The weight given for the Earth in previous posts (actually the Earth�s mass) is the sum of what we would measure if we weighed all of the substance of the Earth, one scoop at a time in standard gravity.

[Tim123]

Weight exists when a body is subject to a gravitational force, but cannot be accelerated by the force. On the surface of the earth, there is a force that would like to accelerate everything towards the centre of the earth at 9.8 ms-2. However, the surface of the earth, or the floor of the building, or the chair you are sitting on, stops this happening, so you and the chair exert a force on each other, and you have weight. if you are in freefall, and there is nothing to stop the force to which you are subjected accelerating your body, you are weightless. The earth is in this situation with regard to the gravitational attraction of the sun and so is weightless. Satellites are in this situation with regard to the gravitational attraction of the earth, and so are weightless. No need to invent the totally bogus and confusing 'centrifugal force'.

[scotstone]

The idea of centrifugal force is a useful concept in engineering as the reaction to centripetal force as required by Newtons third law. Freefall is just an alternative explanation as is Einstein's distortion of space to explain gravity hence weight.