# What's up with default gravity?

Discussion in 'Physics' started by Denisowator, Aug 5, 2017.

1. ### Denisowator

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I googled this a bunch, but found nothing.

Basically I just want to know, why is the gravity in the Physics settings, -9.81 by default? Why that number? Was it tested and found to be the most realistic or something?

2. ### neginfinity

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Because it is the default gravity on planet Earth. -9.8 m/(s^2).
https://en.wikipedia.org/wiki/Gravity_of_Earth

The constant is normally taught in school - during the first year that introduces physics.

I kinda thought that everybody knows that.

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### Digital ApeModerator

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Such a hardcore crowd!

5. ### Ryiah

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You're assuming most of us remember it after we've gotten out.

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6. ### neginfinity

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It is not too far removed from knowing multiplication table, IMO.

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7. ### Denisowator

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Well I never studied physics, not to mention teaching/learning systems greatly vary across the world. Also, thanks for the answer and the link.

8. ### Denisowator

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9. ### neginfinity

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That's unexpected. I thought standard school program is supposed to cover basic physics course.

Meaning Newton Laws of Motion, Pascal Laws, Kinetic Energy/Impulse, Joyles, etc, and in higher grades Ohm laws and basic laws of Thermodynamics.

The "g" (9.8 m/s^2) constant appears as soon as the course reaches "F = ma" and starts dealing with constantly-accelerated motion that gives "v*t + a*t^2/2" formula. I think it was either fourth or fifth grade material.

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10. ### BoogieD

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I guess some studied at the Academy of Uranus.

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Zing! XD

12. ### Denisowator

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In my school, you were forced to learn all the basic stuff (English, Mathematics, History, Geography, etc.) and surprisingly Physics was not one. But then after the 3rd year (or at, I can't remember), you got to pick all your subjects. And I didn't pick Physics, because I don't like all those scary looking formulas and acronyms (cause I don't like having to remember so much different data and information). And speaking of remembering, I actually never fully learnt the multiplication table for the same reason.

There are two really big stereotypes in hero v villain type cartoons. The strong idiot, and the weak genius (nerd). And I'm the former.

Last edited: Aug 5, 2017
13. ### BoogieD

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My school was run amok with kids making gunpowder, cannons, hot air balloons and printing photos in the darkroom all day. There was also stuff the teachers knew about.

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14. ### Denisowator

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That sounds oddly sinister.
And was one of those kids Captain Jack Sparrow?

Last edited: Aug 5, 2017
15. ### BoogieD

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Lots of fun actually. The teachers got to learn a few things from the students and best of all, nobody died.

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16. ### Denisowator

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I can only imagine for how long they saw only green or blue after coming out of the darkroom.

17. ### BoogieD

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Yes, I can still taste the fixer.
Back to gravity. Just remember to use close to real world units (meters) and mass weight (kilograms) otherwise the gravity will not appear to be doing it's thing as you expect. A pile of legos will crash quicker than the twin towers.

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18. ### neginfinity

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I had wider selection of subjects at school, and they were all mandatory (and included physics). I think the one subject I forgot the most is Chemistry. Can remember formula for sulfuric and phosophoric acids, but that's it.

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19. ### neoshaman

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I still don't know my multiplication tables, I was always bad at rot learning, IQ test by doctor show I'm slow at processing informations and have very low working memory, both below average. But I used to be great at schools in anything science, I didn't use the taught method, I used my own heuristic, I was always the first to finish all math assignment, but professor where very disappointed when they send me to the blackboard because I did noting like they wanted me to do, which was the worst example to how the class lol. But then I took a dark turn and got into art ... art is nice, fuzzy and all but I should have invested in programming. DAMN IT.

Anyway your weaknesses can make you more efficient if you don't stop at them.

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20. ### alexanderameye

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@Denisowator did you go to school in the United States? I really recommend studying some Physics, it might seem scary I guess, but you'll learn stuff that might be useful in your daily life! And if you don't want to learn formulas by hear, just don't! Learn about the logic behind physics, learn about why things occur instead of the numbers/maths behind it.

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21. ### DominoM

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Here's a good talk on game physics which should clarify things a bit:

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22. ### RSH1

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Why would you assume every school across the globe follows the same syllabus? Or expect people to remember specific constant numbers taught when they were children?

Obviously not as someone asked this question. What was the point in this reply other than an attempt to berate someone for being curious about something?

23. ### alexanderameye

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I don't think that that was @neginfinity 's intention. He just wanted to express that it's pretty weird that not everybody learns this in school. F=ma is one of the most important formulas in physics so for me personally I also expected that people knew the value of g.

24. ### angel_starr_mauas

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Let's see... There is a physical, mathematical reason that Earth's gravity is measured like that. Earth has mass. In unity there is no mass.
I think it's just confusing. Other than having zero effect on the realism of the physics: because, as I mentioned, you'd have to have a celestial object with Earth's properties in order for that gravity to make any kind of sense.
If the default gravity were set to a simple 1, on the other hand - game developers would be able to actually make sense of gravity.
And IMO it definitely should be set to 1.
Because Unity does not mimick realistic physics. And it never will be able to. We don't have the computing power for it. And it would be redundant, and useless, for games.
More importantly: because game developers are not physicists, and neither do not, nor should not, know any physics - that is the whole point of Unity: enabling ease of development. Making it accessible.
Finally, I find the phrase "I kinda thought everyone knew that" to be vane, and disrespectful honestly.
For example: I know some quantum physics. Imagine if I were to reply to quantum physics related questions with that closing phrase "oh? Didn't you already know that? Didn't everyone?". How would that make people feel?
That's right - it would make people feel ashamed that they didn't know it. Ashamed to ask further questions.
It is counter productive. And rude.

25. ### angel_starr_mauas

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Again: why are we talking physics? Are we pretending that Unity is a physics engine?
How about electromagnetic radiation then? And the gravity calculations: do they include calculations of the quantum gravity between objects of different masses?
How about air? Gasses should also be affected by gravity.
Oh, don't even get me started on the particle system... Which physics rules does that follow?

Unity is not a physics engine.
It isn't meant to be.
And it never will be.
It is a game development platform.
It should be simple. Accessible.
Physics belong in CERN. Or NASA. Not in Yooka Laylee.
I hope my point is getting across.
Gravity should be much more simplified.
As it is now: it is convoluted, difficult, and unrealistic.
It's default value is more like an easter-eggish tribute to real physics.

### Unity Technologies

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You are entitled to your opinions like anyone else but the way you're framing them isn't helpful and just comes across as ranting. Maybe try to rephrase what you're saying would be more beneficial.

Also, to mention that you're doing this on a thread where the last post was March 25th 2018.

Last edited: Aug 25, 2019
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