# Physics at extreme speeds

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Appologies, but my question is a bit general. I'm working on a completely over the top racing game, involving extremely high speeds, between 200mph - 1500mph and above. ( it is heavily inspired by the F-zero series, as well as the anime movie Redline ) Since we are really pushing this as far over the top as we can take it, I would like to pull in some real world physics where possible. For example, after a certain speed, air friction alone becomes enough to ignite an object. What type of physics based considerations would you recoment taking into account? I'm not looking for specific formulas or anything, just any thoughts that might be relavent, or worth considering. Thanks!

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Well one thing you will have to do some worrying about is when you get going really fast - you can't use regular bounding box collisions because you will pass through things. I think some neat real world things would include a sound and a vapor ring when you exceed the speed of sound. Also turing becomes more difficult and the chances of your car losing all traction on the road is quiet high. If you where really going that fast your car would also flip over from the air going under it, but that would be lame to add.

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For example, after a certain speed, air friction alone becomes enough to ignite an object.

It's actually not air friction that creates the heat. It's the compression of the air. The actual friction creates very little heat compared to the compression. (For example, compressing air into an air tank will heat it up, and releasing the air will cool it down).

What type of physics based considerations would you recoment taking into account? I'm not looking for specific formulas or anything, just any thoughts that might be relavent, or worth considering. Thanks!

I'd suggest using continuous collision detection for such great speeds, or else you'll get tunneling (object passing through each other). As for realism, I'd suggest taking air drag into account. Tunnel vision might be an interesting effect to play with.

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I'd suggest using continuous collision detection for such great speeds, or else you'll get tunneling (object passing through each other).

I'm actually really glad you both mentioned this, since it would have completely slipped my mind.

It's actually not air friction that creates the heat. It's the compression of the air.

Interesting. I didn't know that. Thanks! Random side thought, would that mean that in the wake of the vehicle, as the air decompresses it would become proportionately cold?

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I'm working on a high-speed racing game with real physics too  but not quite in the 1500mph range...

One of the first tests I did with our physics engine was to recreate an F1 car and create a track with a corkscrew and loop in it, to test the urban legend that with enough down-force you could drive on the roof. According to my simulation, you can -- as long as you don't slow down, you can drive on walls and upside down (with less grip than when driving on the 'floor'), due to the downforce (or upforce now?) being much stronger than gravity, glueing yourself to the driving surface.

I plan to make use of this to create plausible F-Zero/Wipeout/etc type tracks, with crazy twists and turns, which in theory would actually be drivable with a fast car.

I think some neat real world things would include a sound and a vapor ring when you exceed the speed of sound.

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Very cool. Did you write any of your own physics for it? I'm using Unity, but I don't know it well enough to say if the default physics will be enough.

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For example, after a certain speed, air friction alone becomes enough to ignite an object. What type of physics based considerations would you recoment taking into account? I'm not looking for specific formulas or anything, just any thoughts that might be relavent, or worth considering. Thanks!

I use Bullet. It does not model this phenomena and likely never will. How would I implement this feature? I would implement it on top of the physics object, taking in considerations all velocities and run appropriate logic on need. I guess I would just look up a table so artists can tweak it.

As fun as "real physics" is, it is rarely physically sound, albeit it sure looks like it.

As a side note: you might consider cheating the players, when your internal speed is in m/s but you present them as km/s or whatever. Once the levels are properly authored, it will look and feel the same.