96

So, I learned in physics class at school in the UK that the value of acceleration due to gravity is a constant called g and that it was 9.81m/s^2. I knew that this value is not a true constant as it is affected by terrain and location. However I didn't know that it can be so significantly different as to be 9.776 m/s^2 in Kuala Lumpur for example. I'm wondering if a different value is told to children in school that is locally relevant for them? Or do we all use the value I learned?

you are viewing a single comment's thread
view the rest of the comments
[-] kamills@sh.itjust.works 22 points 9 months ago

We learned 9.82 m/^2. But in the classes I have as an engineering student we use 10 m/s^2. And I wish I was kidding when I say it's because it easier to do the math in your head. Well obviously for safety critical stuff we use the current value for wherever the math problem is located at

[-] huginn@feddit.it 18 points 9 months ago

9.8 is close enough to 10 for most human scale calculations. No need to have extra sig figs

[-] driving_crooner 16 points 9 months ago

Pi = 3

Sin(x) = x

And now, g = 10. Smh.

[-] Tar_alcaran@sh.itjust.works 18 points 9 months ago* (last edited 9 months ago)

I have a "pi^2 = g" shirt, and every engineer I know loves it, every friend with a scheme background needs to point out that it's wrong.

[-] captainlezbian@lemmy.world 6 points 9 months ago

I’ve seen engineers use all of these. Bridges still work

[-] captainlezbian@lemmy.world 4 points 9 months ago

Yeah air resistance is a stronger factor than those .2 m/s2. If we can ignore it we can ignore both

[-] Overzeetop@kbin.social 7 points 9 months ago

Interesting that I learned 32.2 ft/s, but only 9.8 m/s - one less significant figure, but only a factor of two in precision (32.2 vs 32 = .6%; 9.81 vs 9.8 is only 0.1%). Here's the fun part - as a practicing engineer for three decades, both in aerospace and in industry, it's exceedingly rare that precision of 0.1% will lead to a better result. Now, people doing physics and high-accuracy detection based on physical parameters really do use that kind of precision and it matters. But for almost every physical object and mechanism in ordinary life, refining to better than 1% is almost always wasted effort.

Being off by 10/9.81x is usually less than the amount that non-modeled conditions will affect the design of a component. Thermal changes, bolt tensions, humidity, temperature, material imperfections, and input variance all conspire to invalidate my careful calculations. Finding the answer to 4 decimal places is nice, but being about to get an answer within 5% or so in your head, quickly, and on site where a solution is needed quickly makes you look like a genius.

[-] r_thndr@lemmy.dbzer0.com 2 points 9 months ago

Even then, once you figure in a safety factor of 2 or 3 as a minimum, the extra precision really gets lost in the fog anyway.

[-] kamills@sh.itjust.works 1 points 9 months ago

I gotta say, that explanations sounds way better than shrugging and saying "close enough". But then again our teachers usually say "fanden være med det" meaning "devil be with that" actually meaning "Fu*k it" when it comes to those small deviations

[-] Overzeetop@kbin.social 1 points 9 months ago

our teachers usually say “fanden være med det”

There's a lot of wisdom in that. ;-)

[-] applebusch@lemmy.world 5 points 9 months ago

Going to guess civil. I work on space systems and we don't have one number. We have the g0 value, which is standard gravity out to some precision, but gravity matters enough we don't even use point mass gravity, we use one of the nonspherical earth gravity models. It matters because orbits.

[-] kamills@sh.itjust.works 3 points 9 months ago

Nope. Mechanical engineering. So usually we say g=10 and then make the steel a bit thicker and call it a day

this post was submitted on 26 Nov 2023
96 points (95.3% liked)

Ask Science

8465 readers
53 users here now

Ask a science question, get a science answer.


Community Rules


Rule 1: Be respectful and inclusive.Treat others with respect, and maintain a positive atmosphere.


Rule 2: No harassment, hate speech, bigotry, or trolling.Avoid any form of harassment, hate speech, bigotry, or offensive behavior.


Rule 3: Engage in constructive discussions.Contribute to meaningful and constructive discussions that enhance scientific understanding.


Rule 4: No AI-generated answers.Strictly prohibit the use of AI-generated answers. Providing answers generated by AI systems is not allowed and may result in a ban.


Rule 5: Follow guidelines and moderators' instructions.Adhere to community guidelines and comply with instructions given by moderators.


Rule 6: Use appropriate language and tone.Communicate using suitable language and maintain a professional and respectful tone.


Rule 7: Report violations.Report any violations of the community rules to the moderators for appropriate action.


Rule 8: Foster a continuous learning environment.Encourage a continuous learning environment where members can share knowledge and engage in scientific discussions.


Rule 9: Source required for answers.Provide credible sources for answers. Failure to include a source may result in the removal of the answer to ensure information reliability.


By adhering to these rules, we create a welcoming and informative environment where science-related questions receive accurate and credible answers. Thank you for your cooperation in making the Ask Science community a valuable resource for scientific knowledge.

We retain the discretion to modify the rules as we deem necessary.


founded 1 year ago
MODERATORS