Conservation of Momentum in vehicular collisions is incorrect

I was driving up to a gas station in a comparitively light-weight SUV at quite low speed (<20kph) and accidentally clipped the mirror of a much larger meth van sitting in the road.

This was sufficient to accellerate the meth van to some considerable velocity, propelling it around 20 tiles and causing it to spin out off the side of the road. On the way the meth van hit an even larger Bus, which itself was then hurled some 30 tiles down the road before finally coasting to a stop.

Bearing in mind that the collision force wasn’t even enough to break the wing mirror on the Meth van, the force imparted on it and then to the far more massive bus seems outrageously high.

1 Like

I can’t reproduce on a recent experimental: hitting a parked Meth Lab with an SUV at 20 kph caused nothing to happen, and even hitting it at 35 kph caused it to move a single tile before coasting to a stop.

There was a bug in the code for a while where parked vehicles had a static drag deceleration of -3 mph, which caused them to continuously accelerate when hit. That’s been replaced by a static deceleration of 15 mph and they don’t move much when hit.

1 Like

Yeah, I crashed a beetle into the side of a luxury RV and all it did was demolish the front of the beetle and the hind of the RV, at about 64 mph (Over 100 KPH). It seems a little cheesy, but a beetle is like a fourth of the size of a RV so I guess it’s not much of an issue.

The assumption is that vehicles have their parking brakes on and those brakes are good for 15 mph/turn of deceleration. That’s not true if a vehicle’s engine is running, so you’ll see slightly more spectacular crashes if the other vehicle has its engine running.

At some point, I’d like to figure out a way to model the difference between static friction and kinetic friction, but it’s a fair bit of work due to the code structure.

1 Like

Yeah, in this case even working under the assumption that the vehicles were completely frictionless they were moving FAR too fast and causing quite substantial amounts of damage to each other - all initiated by a collision that would barely be sufficient to knock over a pedestrain IRL.

Worse, each successive collision seemed to be ramping up the total kinetic energy imparted. If I lined up 10 free-rolling vehicles in CDDA and gave the one in back a love tap right now, I kind of suspect that the 10th one in line would either end up a cloud of shrapnel, or would exit the map at supersonic velocities.

1 Like

Is this still happening on a recent experimental, from the past two days? There was a bug but I thought the bug had been fixed. I’d like to know if that’s not the case.

I’ll check when I get home, but I’m pretty sure it was the 0.D stable release, windows tiles - so if you’ve already addressed this in experimental versions, you’re probably fine.

That’s a pretty good sanity check, we can probably add that.