g on the moon != g on earth, they're completely different values and hence once subbed in the meaning of the equations gets limited to "only valid on X planet's surface".
Quoteg on the moon != g on earth, they're completely different values and hence once subbed in the meaning of the equations gets limited to "only valid on X planet's surface".
That was my point. My 'mass' (using 75kg) is the same throughout the universe and can't change (unless I eat lots of food while venturing around space). a = g doesn't only exist on Earth, but can exist anywhere in the universe too.
So saying because we are on Earth, and acceleration due to gravity is 9.8, then ma = mg, isn't really correct.
So saying because we are on Earth, and acceleration due to gravity is 9.8, then ma = mg, isn't really correct.
So saying because we are on Earth, and acceleration due to gravity is 9.8, then ma = mg, isn't really correct.
It is correct, but only in certain situations. Basically no equation is truly universal, all have limitations.
f = ma <-- only directly usable as an approximation between a very large mass (earth) and a very small mass (eg a person) OR between two very distant bodies where their radii are much less than their seperatory distance. Otherwise the results are quite wrong (you have to break each mass down into smaller pieces & integrate the results instead).
f = m * 9.8ms-2 <--- all of the above restrictions, but now also only valid on the earth's surface (and technically in some other places in the universe, but this explanation is good enough)
f = 75kg * a <--- only valid for things of that weight, eg approx a human
f = (width * length * height * density) * a <-- only valid for rectangular prisms of constant density
I'm trying to understand exactly why ma = mg.
Obviously ma = mg in this case. After reading, it's equal because we are on Earth. If I weighed myself on the moon, then ma = mg, however, if everything is relative to gravity on the moon, then ma = mg on the moon. For the most part, ma would equal mg anywhere in the universe providing gravity and acceleration are the same.
Am I missing something in the translation of why ma = mg?
I'm trying to understand exactly why ma = mg.
I took physics, and, the concept of weighing myself on the scale and learning it's really our mass, I'm confused about ma = mg (this began after watching the Big Bang Theory).
...
Physicists aside, we treat gravity as a force because it matches our everyday language, and makes sense of our everyday experience. But it is a misleading line of thought, according to General Relativity.
https://www.universetoday.com/108740/how-we-know-gravity-is-not-just-a-force/
Generic Newton's force formula:
F = m * a
Weight force on any planet (substitute a with gravitational acceleration):
Fplanet = m * gplanet
Weight on any planet in kg:
weightplanet = m * gplanet / 9.81
I am consistently amazed at the tangents and minutiae that appear in response to such a simple question....
Obviously ma = mg in this case.
We only wish to emphasize here the following points: (1) the electromagnetic theory predicts the existence of an electromagnetic mass, but it also falls on its face in doing so, because it does not produce a consistent theory—and the same is true with the quantum modifications; (2) there is experimental evidence for the existence of electromagnetic mass; and (3) all these masses are roughly the same as the mass of an electron. So we come back again to the original idea of Lorentz—maybe all the mass of an electron is purely electromagnetic, maybe the whole 0.511 MeV is due to electrodynamics. Is it or isn’t it? We haven’t got a theory, so we cannot say.
We must mention one more piece of information, which is the most annoying. There is another particle in the world called a muon—or μ-meson—which, so far as we can tell, differs in no way whatsoever from an electron except for its mass. It acts in every way like an electron: it interacts with neutrinos and with the electromagnetic field, and it has no nuclear forces. It does nothing different from what an electron does—at least, nothing which cannot be understood as merely a consequence of its higher mass (206.77 times the electron mass). Therefore, whenever someone finally gets the explanation of the mass of an electron, he will then have the puzzle of where a muon gets its mass. Why? Because whatever the electron does, the muon does the same—so the mass ought to come out the same. There are those who believe faithfully in the idea that the muon and the electron are the same particle and that, in the final theory of the mass, the formula for the mass will be a quadratic equation with two roots—one for each particle. There are also those who propose it will be a transcendental equation with an infinite number of roots, and who are engaged in guessing what the masses of the other particles in the series must be, and why these particles haven’t been discovered yet.
But then it is spoiled by this:QuoteWeight on any planet in kg:
weightplanet = m * gplanet / 9.81For starters, kg is a unit of mass - not a weight. Secondly, what is that divide by 9.81 all about?
So saying because we are on Earth, and acceleration due to gravity is 9.8, then ma = mg, isn't really correct.
It is correct, but only in certain situations. Basically no equation is truly universal, all have limitations.
f = ma <-- only directly usable as an approximation between a very large mass (earth) and a very small mass (eg a person) OR between two very distant bodies where their radii are much less than their seperatory distance. Otherwise the results are quite wrong (you have to break each mass down into smaller pieces & integrate the results instead).Excuse me? F = ma is one of the fundamental laws of Newtonian mechanics. It is always exactly true, without exception, in a Newtonian framework. What makes you think it is an approximation?
Also, how do I insert LaTeX formulas in this forum?
To do displayed math, just put it between double dollar signs. I don't know if there's a way to do it inline.
One thing we can all agree on is mass remains constant, it can't change throughout the universe.