I am curious... how accurately have we weighed things? Is there a point where the weight of an object will not stay still? To see this, I imagine, we would have to weigh something in grams to something like 20 decimal places and it would have to be somewhere completely devoid of vibrations. Is there an accuracy point where the weight is no longer fixed... where we would have to calculate the average weight rather than know the exact weight?

Gravity flucuations will cause the weight of an object to vary.

Plus, I suppose, the moon being overhead would cause the weight to be less for the same reason that the moon causes the tides.

Weight in a more formal definition is the "normal force" acting on an object given that the object is placed on a surface that is perfectly parallel to a plane tangent to the Earth's surface at the point of weighing. This normal force will ensure that the object remains basically unmoved. It will fluctuate depending on the forces on it that are trying to make it move (gravity mainly since we've taken out vibrations and wind).

 

As mentioned, the precision in which you can measure an object's weight will be hindered by the gravitational fluctuations present. If you are going to precision approaching infinity, you will need to take into consideration the presence of the Sun, planets and possibly all stellar objects. Oh, and the bulging of the Earth as well as other assymetries (non-homogenous density) that will cause the gravitational field to vary on the Earth's surface.

we would have to weigh something in grams to something like 20 decimal places

 

Just a quick note weight is measured in units of Newtons, not grams, this is a unit of mass.

Gravity and weight are the same thing. Weight is the result of the gravitational interaction.

OK... what I was wondering is this...

 

Is it possible that mass (we'll say on the surface of the Earth, for example), at a small enough scale, actually has a kind of brownian motion? And it is only the NET or AVERAGE motion that is seen to be 9.8m/s/s in a downward direction?

 

I believe this would cause slight variations to occur in the sufficiently accurate) measured weight of a (sufficiently small) object.

 

OR

 

If the mechanism of gravity was something akin to gravitons, then each graviton would have its own effect on a small bit of matter. A kind of a tug (let's say). Many gravitons cause many tugs, and together they would create (on OUR much larger scale of matter and time) an apparantly smooth acceleration of 9.8m/s/s

 

If we were to measure an (again, sufficiently small) object accurately enough, shouldn't we be able to detect a 'jerkiness' in it's weight due to the individual gravitons?

Also, the apparent wieght of something may vary simply because the equipment used for measurements could be inaccurate. A downward draft can significantly through of a weight, especially for smaller scales and smaller wieghts. That's why most labs have glass cases to protect the scales from this phenomenon.

My weight seems to vary quite often. Just yesterday, one of our secretaries commented that I had lost weight recently.

If you kept all gravity the same, weight would not vary, however, this is near to impossible, as you can't just ask a planet to stop moving

If you kept all gravity the same, weight would not vary, however, this is near to impossible, as you can't just ask a planet to stop moving

 

No, you can't ask a planet to stop moving, but assuming you could, or better yet, assuming you could account for the effect of the motion of all these bodies in your measurement, how do you know that the weight of an object would not vary (or fluctuate) at a precise enough measurement?

 

Is it a definite consequence or law of field theory that gravity is fixed.. even down to planck scales?

 

And what about quantum theories of gravity... with the graviton involved, gravity is still smooth? Still an exact figure no matter how precisely you measure it?

how do you measure an object's mass if there is no gravity?

how do you measure an object's mass if there is no gravity?

 

Sorry, that's just my 'signature'... I've changed it now... should be less confusing.

 

 

(edit- my signature was 'there is no gravity... just inertia'... to answer the question, my signature should have (more accurately) said something like : 'Gravity is just inertia' since, of course, there IS gravity.)

Gravity and weight are the same thing. Weight is the result of the gravitational interaction.

 

Incorrect. Weight is a measurement of how much a certain mass is affected by the gravity that is applied. A classic example are olympic records that are achieved in places farther away from the earth's center. Your weight changes on how far you are away from the earth's center. You're mass is constant, but the gravity is changing, thus you're weight is directly proportional to your mass and the gravity acting upon you. This is why you're weight changes from planet to planet as well, and why you are *basically* "weightless" in space.

 

Also, you can most likely measure mass without gravity in the equation. Gravity and Mass demonstrates weight.

"how do you measure an object's mass if there is no gravity?"

By producing what is equivalent of gravity: apply a force and measure its acceleration.