Close enough I graduated last year 2023. I couldn’t get in to the college I wanted so I decided to try it a second time. There’s a countrywide exam that gives you a score. It’s called yks. I’m currently studying for that exam.
Rounding of constants always depends on what you are calculating. Getting a rocket into orbit is a case to use the actual local value of g with a bunch of digits (and the change with height, too). If you build a precision tool, some more digits of PI are no bad idea.
But to calculate the lenght of fence to buy to surround a round pond, I actually used 10/3 for “PI plus safety margin” once.
Not necessarily. The two things aren’t related. You yourself burn way more calories in a year than you store in your body or use for growth. Respiration is not just about growing. It’s about using energy for cellular processes: immune system, transporting chemicals around the organism, replacing old cells.
An organism can grow at one rate and use energy (expelling CO2) for other functions at a different rate. They aren’t really related.
They are related, because the energy they use and the mass they grow both come from absorbed CO2.
In other words, every molecule of CO2 expelled by a tree was previously absorbed by the tree. Unlike humans, energy use by trees is carbon neutral. Which means trees cannot grow unless they absorb more CO2 than they expel.
I’m not sure, why you’re interpreting my comment as a general statement. I’m specifically talking about trees. While it’s theoretically possible that they get carbon from the ground and actually respire more into the air than they absorb, while also growing wood, that would be extremely surprising to me. Unless there’s data supporting it, I don’t see why we should entertain the thought…
That makes no sense. The human body is on average carbon neutral. You eat carbon and then you excrete it. Same as trees. Except you don’t continuously grow like a tree for potentially centuries.
Of course it is. No carbon was created. And unless you’re putting on weight, your mass stayed the same. Carbon in, carbon out. I’m not talking about CO2 neutral.
I’m not making up any shit wth? How dense are you? A tree is carbon negative because it sequesters carbon continuously. A human adult is not, it’s carbon neutral - when observed in isolation. The human system is carbon neutral. It doesn’t matter where the car on comes from. You expel the same amount as you injest. I think honestly you’re the one who doesn’t understand what carbon neutral really means.
Turning carbon in the environment into CO2 by oxidizing it is NOT carbon neutral! If that was the case, then every car, plane, and coal power plant would be “carbon neutral”. That’s very obviously not the case.
Being “carbon neutral” means that you, or the operations of your business or your national economy, emit the same amount of carbon dioxide into the atmosphere that you offset by some other means. (Source)
It’s ALL about CO2! For the love of god, go read some articles. You have no idea what you’re talking about.
The next time someone says that to you - point to a tree and explain that - that thing over there is largely comprised of carbon that has been extracted from the atmosphere by photosynthesis- so what are you talking about?
Yeah, it’s the simplest answer, and likely correct. But a more interesting question is why they got it wrong and what assumptions and misconceptions did they make to arrive at the wrong answer.
Well, g is not a real constant, it depends mostly on altitude. The true constant is G. g=9.8 is usually more than enough for your calculations, to the point we often round it to 10 for simplicity, or you remove it completely is the mass is too low. But actual numbers is only the very last step usually. The calculations will be made with letters. The value you use at the end for g depends on the precision you need, so it depends on the precision of the other parameters.
This doesn’t change the issue presented by OP. Sea level is not level across the world. In fact there are much larger differences than most people expect. The Earth is not perfectly round. Earth rotation causes the equator to be affected by a centrifugal force, making it wider there ( more distance to earth core means less gravity ) than at the poles. Overall, gravity at Earth surface level varies by 0.7%, ranging from 9.76 in Peru to 9.83 in the Arctic Ocean, but it’s absolutely not linear. In addition, the Earth is full of gravity anomalies. These cause localized dips and spikes in gravity. Two of the big dogs lips lie in the Indian ocean and the Caribbean. Because water is fluid, sea level is very much affected by local gravity (as well as other factors such as air pressure, salinity, temperature…). Which is also why the moons gravity can cause tides. The permanently lower gravity on these anomalous spots mean that the average sea level here is lower than it would be on a perfect sphere. This difference can be up to two meters in sea level.
G is the gravitational constant, the m’s are the masses in question, and F is the force generated. The r is radius from the center of one body to the other; that is, height. If it didn’t decrease, orbits wouldn’t exist the same way and astronomers would have laughed Newton out of the room.
I could give you a link if you really want, but it’s the Newtonian gravity equation, so it’s probably just going to be “Gravity” on Wikipedia.
G is also fixed in GR, although it’s not guaranteed to manifest in a neat relation like that in every situation because spacetime curvature has a lot of components at every point, and they interact super nonlinearly.
we learned it was about 9.8. We actually measured what it was near our school, and I think it came out to 9.82. We were told it was ok to use either 9.8, 9.82 or 10 in exams.
While I don’t know the answer and that for simplicity it should probably be a global average, it is probably some “constant“ measured from some location in either Europe or North America before they were able to measure globally using satellites.
This reminds me of the story of magnetic detonators for torpedos they tried to use in the early days of WW2. They detect the slight disturbance in the Earth’s magnetic field caused by a gigantic hunk of floating metal, and that triggers the detonation.
However, they did not yet know that the Earth’s magnetic field is not consistent over the whole planet, so while they calibrated it to the local field, it functioned very badly in other regions with different field strengths. Torpedo would either detonate far too early, doing minimal damage, or not detonate at all, just hitting the target ship with a loud thunk.
This was largely responsible for the ineffectiveness of American submarines in the early days of our WW2 involvement. Took us a couple years to sort too.
It was called the Mk 42 in case anyone wanted to read a little more. It’s an amusing story. They never wanted to actually properly test them, because they were so damn expensive. So they just didn’t. lol It wasn’t until enough sailors complained and got a high ranking admiral on their side that it got sorted.
People learned different values for g for a number of reasons, but as far as I understand local variability is not one of them. The primary root cause seems to be accuracy of the measurement over time and the age of textbooks/course material.
Over time we have gotten better at measuring the true value of g through advances in technology and this has caused the taught value to shift a little. The value when initially measured had fairly large error margins, meaning that we were sure it was near a specific value but not sure of the exact value. As the tools improved we have reduced the uncertainty, getting to a more accurate and also more precise value, meaning more digits after the decimal as well as higher confidence in each digit. We have also changed what we mean by g over time, bringing it in line with the metric system and basing it on fundamental values and constants. From my understanding the most recent method relies on how much the repulsive force of an electromagnet with a specific number of culombs passing through is overcome by gravity at a specific distance from the center of the mass of Earth, so a little more removed from backyard science than measuring if things drop at the same speed at the top of a mountain and sea level.
Part 2 is the differences in how recent your material is. In my primary school in a relatively affluent area of an affluent country we had textbooks from the last 10 years. My partner went to a school in the same country but a worse area about 5km away from mine. Their school had textbooks literally 20 years old. In that time the measurements had changed, understandings had changed, and they were therefore taught things that were untrue. These sorts of differences based on geography reproduce the impacts of racism and inequality from the past into the future.
Yeah. 9.8 is what I learned. I was generally aware that locality made a difference, but I had no idea that there was that much of a spread. For anything not involving millions of dollars of rocketry and actual satellites a simplified number is likely good enough. Much like Pi, where a couple digits is good enough for most everything and calculating out past 6 digits or so is infinitesimally small.
I coudn’t find a source for your statement, but I did find that it takes a tree 30-40 years to store a ton of CO2, so maybe that’s what they mean? A tree will store carbon as it grows, because it builds itself with carbon from the air. ecotree.green/en/how-much-co2-does-a-tree-absorb
I think there has to be a certain balance. We can’t just cover a massive field even in trees, that creates an unhealthy ecosystem.
Sometimes, as we try to fix things quickly, we miss or ignore the long-term consequences.
It is probably a statement related to the average tree. Also, I believe hemp and bamboo are not trees (but I’m also not a plant scientist) so not really relevant in a statement about trees.
Ehh, cannabis is a woody annual. At least that’s what I’d call it. It dies every season. In some places a stand can reseed itself or a mother plant or two may overwinter for a maximum of one season by being buried under it’s daughter plants after they collapse from senescence, essentially cellular death from old age, which varies by species.
Hi there! Can you please remove the word “retarded” in your first sentence? This word is now generally considered a slur, which runs afoul of rule 6 “Use appropriate language and tone. Communicate using suitable language and maintain a professional and respectful tone.”
Not your fault, but that is the most annoying calculator I've ever encountered, as someone who uses the metric system.
I mean, what kind of maniac describes the amount of oxygen produced in pounds?
Also are those US gallons or UK gallons?
The increments used for the circumference of the tree is also incredibly weird, 7 and 3/4 inches? Really? Clearly converted metric to imperial. Why not include a slider to switch to metric, if that's what you've based your numbers on?
Probably because the writer is not reporting her own original research. She is reporting work done by others, they often used metric, and any metric units were converted to common US units because the article was intended for a general American audience.
And why isn’t there a button to restore the original metric units? Same reason why when a newspaper reports a translated quote from Macron or Putin or Xi, there is usually no button to restore the original French or Russian or Chinese: the editor decided that it wasn’t necessary for the intended audience.
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