TF2 Physics Lesson: The Laws of Force
It appears once again I over presumed and rushed everything, meaning this article is, for lack of a fancier word, wrong. Please scroll through the comments for Drexer’s post regarding this. For the next day or so I’ll keep the article up before deleting or overwriting it. Can’t say how sorry I am folks. -oldmeme
Before you go on reading, this article goes into some of the minuscule areas of the game and may not entirely affect gameplay for everyone, but is nonetheless interesting.
With the scout update leaving a funny taste in most players mouths, we are starting to see the slow decline now in the number of scouts (and those bloody Sandman Scouts). But of all the unlockable weapons release, including the other classes, the Force-a-Nature is by far my favorite. Simply because it loves being different. Its not a mere take “one positive trait and add a new one”. It is almost an entirely different weapon in terms of Scout playstyle. But I’m not here to talk about that. I’m here to talk about the levels for force the FaN exerts when you shoot it for that little extra jump.
To begin, lets look back to pre-Scout update. All you had was a little Double jump. Now imagine yourself jumping from a sizable height and saving your health by executing the double jump. If the ledge is high enough, you will actually lose speed from using the double jump to save yourself.
This is because the force given by jumping goes at a range of somewhere around 80 to 90 degrees of an angle upward. Not to the side. Now to give out that force, the computer needs to give out a strong enough opposing force to let you jump the same height every time. For example, as a Scout, whether I fall a 100 meter height, or 5 meters, I will always reach the same height when I use my double jump to break the fall. This is done by the computer, who comes up with an opposing variable force that will always be equal to x, the exact height the scout reaches with a double jump. This force is variable because of Valve’s handy physics engine that is close to real life physics, gaining speed as you fall, before attaining a constant velocity from falling in those extreme height custom maps.
Here is a handy little picture to show what I mean:
Now this is all well and good, it means you will always get the same height from a double jump. But the interesting fact is that Valve did the very same thing for the Force of Nature (FaN). “What does that mean?” you ask. It means the faster your velocity while in the air, the more force you release to gain the same height every time when you shoot directly down, just like the double jump.
Basically this is a copy paste of the above, but the with the FaN, is that the force is not fixed to a centered direction. You can aim and angle this force. So the force the computer works out to oppose my falling force (I took this to be Kinetic Energy for those following the physics side of this) must be equal to x, were it going straight up. In this case, the force is instead used at an angle and is so great in power, it flings you around like a mouse to a tennis racket.
Again, a helpful picture:
This is why when you double jump and instantly shoot, the opposite direction you are traveling in you do not fly forward. In fact, you lose speed because you are not falling at a fast enough. So if I double jump in one direction, then instantly shoot, I lose variable speed. But if I jump from the second or fourth point on Badlands, and then shoot at a 45 degree angle downward right before I hit the ground, my multiplied force is exerted sideways. Meaning you get a sharp boost of speed that is faster than scouts running speed.
This may or may not be implemented in-game very well, but I did find it incredibly handy on maps like cp_badlands and pl_badwater which had loads of high drops to manipulate this little feature. Try it for yourself and give a comment if you have have had any fun with it already. As always, thanks for reading.
Disclaimer: Unfortunately, this implementation is capped and will not let you shoot yourself to infinity and beyond. The biggest difference will depend on current speed and the angle of which you shoot, best I think at that sweet spot of a 45 degree angle. Use with caution. Not intended for children under the age of three.
Pictures were made by me using Photoshop CS2 and Garry’s Mod. I wanted to work out a sum for this but I am still only through my first year through secondary school Physics and did not get very far… (something along the lines of Ek ? ????Ek = x) . If you are up for the challenge, leave it in the comment box or on the forums. Thanks to indivisible who made an attempt at it for me 
EDIT: Spelling mistakes off the port bow cap’n!
Stumble it!
clubtheseals responded on 18 Mar 2009 at 8:06 am #
YOU’RE BACK! HALLELUJAH!
oldmeme responded on 18 Mar 2009 at 8:08 am #
Mr. Noobinator responded on 18 Mar 2009 at 8:18 am #
i don’t get this at all.
The Luaper responded on 18 Mar 2009 at 8:25 am #
Another interesting fact, if you shoot the FaN directly UP while in midair, you get the same effect as a shot strait DOWN.
oldmeme responded on 18 Mar 2009 at 8:30 am #
@The Lauper
Discovered this today myself when I shot at a mid air Soldier above me, only to fly into his face and get a point back crit shot @_@
Polterjunge responded on 18 Mar 2009 at 8:31 am #
I saw the pictures first and had a look at the official TF2 blog whether they’d released a new post. But then I realized you made them yourself. Good work.
Although, the topic is really geeky ^^
Ozcar responded on 18 Mar 2009 at 8:33 am #
Well, if you’re just wondering about the upwards jump and the “physics” behind that, I’d guess that the boys at Valve simply mirror the velocity of the Y-axis and add a constant that gives it some specific height. With the help of FaN you can direct that stream of extra velocity and thus achieve a speed of v(y) + v(const), which may well be bigger than scout’s normal running speed. I’m not saying this is how it’s really working, it’s just how I would’ve done it.
VEKrueger responded on 18 Mar 2009 at 8:34 am #
Very interesting. I love exploring this like this in-game, even if they don’t completely adhere to the laws of physics. Good read.
n00bie51 responded on 18 Mar 2009 at 8:37 am #
oldmeme, something tells me that English isn’t your first language. Excuse me for nit picking:
1. It’s “affect,” not “effect.”
2. It is “nonetheless,” not “non the less.”
3. You abbreviate it as FaN, so I think you KNOW that it’s correctly termed the Force-a-Nature, not the “Force of Nature,” but for some reason you choose to call it that way.
4. It’s “lose,” as in loss, not “loose,” as in not tight.
There’s probably more that I missed, but whatever, it was an interesting article.
HelisPoe responded on 18 Mar 2009 at 8:40 am #
Confused Tf2 player is confused. Effort at explaining physics of game engine confuzzles me.
oldmeme responded on 18 Mar 2009 at 8:41 am #
@n00bie51
But my Inglish techer tolde me my Inglish is very good?!
Yes, I’m terrible for speeling mistakes, and I tend to drift while typeng.
And only found I spelt the Force-a-nature (I’m a big boy today!) like how I said it sadly. My fault entirely. A redo is in order methinks…
n00bie51 responded on 18 Mar 2009 at 8:49 am #
By the way…
Retarded grammatical meme is retarded. Though I can certainly appreciate the absurd shenanigans of memes, I do not find this particular one to be amusing whatsoever. Perhaps I’m missing something, but how is using the same adjective twice in one sentence supposed to be funny?
Stupid nonsense meme is stupid and nonsense. HAHAHAAHAHAHAHAHAHAHHAA!
kanodin responded on 18 Mar 2009 at 9:19 am #
Fascinating, I had noticed a small part of this effect while playing on watchtower but lacked the necessary background in physics to describe the how and why.
I’m trying to think of a few other maps where this would be useful, egypt springs to mind, as do parts of hydro.
Also Noobie, memes are not created because they are funny, they are created because they are malleable, hard to forget, and easy to repeat, any humor they creates are at most coincidental.
Corodan responded on 18 Mar 2009 at 9:27 am #
I enjoyed this a lot. Geeky physics lessons in video games requiring shotgun blow back is ALWAYS fun to read!
n00bie51 responded on 18 Mar 2009 at 10:07 am #
Personally, I consider memes to be similar to inside jokes (although on a larger scale), and therefore, are supposed to be (or usually are) amusing and humorous.
The Black Watch responded on 18 Mar 2009 at 11:05 am #
Being a second year Physics student. This makes complete sense. And though I was aware of it, I didn’t really think to make an article on it.
kanodin responded on 18 Mar 2009 at 2:14 pm #
inside jokes are only funny because they basically reference a funny shared moment, so I suppose I can see that as being applicable to memes referencing to a funny mistake or something ridiculous.
However inside jokes remain funny because you can physically see the other peoples responses which are themselves amusing, the anonymity of the internet immediately removes that.
Further while the initial phase of a meme is a reference to this theoretical silly event, the spreading of it has no relation to this event. It is instead people mindlessly parroting what others find funny without the reason why, followed by the people they parrot it too further spreading it and thusthe original joke has been completely submerged in this sea of repitition, causing those who originally thought of it to grow bored and annoyed by it.
And that is what I meant by humor being coincidental to memes. I may not have a good background in physics, but I know my comedy and memetics and know that they do not mix well.
kanodin responded on 18 Mar 2009 at 2:16 pm #
Oh and that was completely irrelevant to all the article but the author’s name.
Secret Agent Clank! responded on 18 Mar 2009 at 5:27 pm #
You get to do more classical physics in your second year? You mean I won’t just move on to more electric and nuclear forces? =D
The case for the Sandman | ubercharged.net responded on 18 Mar 2009 at 8:00 pm #
[...] and this just made my brain hurt, so I’m ignoring it because I can. [...]
P4TCH responded on 18 Mar 2009 at 8:29 pm #
Nice find…I didn’t know it, and using scout as my main this will come in handy
dekichan responded on 19 Mar 2009 at 4:04 am #
this is my favorite kind of post. It highlights a facet of play that allows one to understand the game better.
Simplified, the faster you are falling, the more the FaN will knockback.
Would the knock back be then adversely affected by low gravity servers?
finally, everyone saw the new how-to vid in the steam forums about new places to triple jump too?
Drexer responded on 19 Mar 2009 at 10:12 am #
Actually, after a lot of testing even with the help of Dracula Guy and after consulting Black Watch and he doing some independent testing too, it seems to be that the conclusions in this article are incorrect.
Considering that this is a videogame and not real life, I should note that the Source engine works with values of velocity and not acceleration(Force). Thus, when you double jump, the engine simply assigns you a certain value for your vertical velocity. Acceleration only works on effects such as air resistance(although that probably is something along the lines of “if(verticalspeed>x)verticalspeed=x;”) or similar.
The vertical velocity which you get from a jump, double jump or fan shot is always the same from the various test performed. that’s why if you stand on the small train car connector that sticks out from cp_well traincars, you can triple jump into the top of the train cars, either by aiming the FaN up, down, or in any direction except the train car(because that would get you away form it obviously).
Apparently the angle at which you shoot the FaN only differs the horizontal velocity at which you are thrown.
As such, I also present here a formula for the distance traveled by a scout depending on the moments when he double jumps or shoots his FaN. Assuming he’s trying to move forwards of course.
x = vx.t2 + vF.cos(?).(vy/a + SQRT( (vy.t2-a(2.t1^2+t2^2-2.t1.t2) / a ) + (vy/a)^2 ) )
x being the Scout’s position as he lands on a surface on the same level as the starting one.
vx being the horizontal velocity of the scout when normally walking/jumping.
vy being the vertical velocity of the scout when starting to jump.
vF being the speed that the FaN gives to the Scout when fired perfectly horizontal to him.
? being the angle between the horizontal axis and the direction the FaN is pointing to.
t1 being the moment when the Scout uses his double jump.
t2 being the moment when the Scout fires his FaN.
a being the value of the acceleration of gravity.
This formula only works if the scout does not land at any moment in between the jumps. Not considering air resistance and terminal velocity.
m1ckyf1nn responded on 19 Mar 2009 at 10:43 am #
Nice diagrams oldmeme, so good in fact that I went to the official TF2 blog because I thought there had been a post!
oldmeme responded on 19 Mar 2009 at 11:24 am #
@Drexer
I’d be lying if I said this did not bother me, but it appears I have been proved wrong
Very well done.
I really cannot describe how foolish I feel, nor can I appologise enough to those who I have misled with the article. I’ll either delete this article soon or write over it with Drexer’s formula.
Speaking of which, Bravo to those who managed to counter my iffy science and coming up with a working formula
Drexer responded on 19 Mar 2009 at 11:48 am #
@oldmeme
No problem. Either way I’ve yet to revise my formula, so there might be one or two things wrong with it. it was jsut a 5 minute work during a class. Don’t delete this article thought, it’s a grand try at explaining TF2 physics and it should not go unnoticed.
If you want to, contact me through Steam and I’ll just provide you with the data I have as well as my conclusions more in-depth. You might even find another explanation that has eluded me.
This was nonetheless, a very well written and thought of article.