Incorrect Physics in Call of Cthulhu!

[Kai Lord]

Add to this the simple fact that the news media will generally show the more damaged of the two vehicles in a report and you see how this misperception can happen. We all remember those rules of the road movies from high school that show the car completely destroyed in an impact. What they rarely ever showed you was the semi trailer that had a dented bumper and broken headlight and that was about it.

That's because the semi was just a decoy; it was only carrying sand.

 

[Rowenstin]

Yes, the book is utterly wrong and don´t take in account relativistic effects. From that point of view, two cars crashing at 250000 km/s each one is the same as a car that crashes into a brick wall at 500000 km/s which is absolutely impossible. So, by the book, the cars dont crash and no damage is dealt

 

[Blacksad]

Yup. You do have double the kinetic energy. Divided by two cars, that makes, for each car, exactly the same kinetic energy as if one of them hit a brick wall. If each car suffered double damage, it would mean quad damage in total. Which means four times the kinetic energy. That's wrong.

isn't kinetic energy equal to (m*(v^2))/2 ? thus when you double the speed, or when two cars drives in opposite direction with the same speed, you have four time the original energy, divided between two cars, it effectivly double the damages, doesn't it?

As far as I know, the Cthulhu rules seems correct.

 

[Ulrick]

African or European?

African or European car?

heh heh

Ulrick

 

[applenerd]

Any use of an equation in a rule is going to be far more unpopular than an technically incorrect rule using addition. Addition is easy. Equations take more time and impede forward progress in the game by that much more. The whole idea of rpg's is to abstract the "reality" of the gameworld into a set of easy to run mechanics so that players can concentrate on the important part, the roleplaying.

 

[Blacksad]

Any use of an equation in a rule is going to be far more unpopular than an technically incorrect rule using addition. Addition is easy. Equations take more time and impede forward progress in the game by that much more. The whole idea of rpg's is to abstract the "reality" of the gameworld into a set of easy to run mechanics so that players can concentrate on the important part, the roleplaying.

I don't know how the design team of Starship (or Warship) for Alternity would react to such a statement

 

[Castellan]

isn't kinetic energy equal to (m*(v^2))/2 ? thus when you double the speed, or when two cars drives in opposite direction with the same speed, you have four time the original energy, divided between two cars, it effectivly double the damages, doesn't it?

As far as I know, the Cthulhu rules seems correct.

I think a lot of people might have missed the URL in my original post. Go to http://www.farmingdale.edu/~kramerpr/teaser/head-on.html abd check out the well-written explanation why the CoC rules are wrong.

Ultimately, using equations in a game is a bad idea. The end result is that you should probably either (A) add the two speeds together and divide by two (even though this is technically wrong), or (B) treat the head-on collision as if both cars hit a brick wall (i.e. if car A is traveling at 50 MPH, and car B is traveling at 70 MPH, car A takes the appropriate damage for a 50 MPH collision, and car B takes the appropriate damage for a 70 MPH collision.

Neither of those solutions is correct in the Real World, but adding the speed together and applying the damage to both parties is grossly incorrect, and unfair to the imaginary passengers therein! Therefore, I'd probably use one of the two above adjustments.

Hmmm... Any physicists want to get together for a Physics CoC game? I can see it now:

GM: Okay, Phil, you hit the cultists with your 1984 Mustang at 43 MPH, coming off of the entrance ramp onto the highway. Let's see, that looks like a 15-degree angle to me --.

Phil: No way! That's easily a 17.5-degree angle, and don't forget that the on-ramp has a downward grade of 1.2-percent! Oh, and Lisa's character ate that burrito just before we got into this chase, so we need to take into account her weight difference, too!

GM: Okay! Okay! *punches scientific calculator a few times* Now the cultists are in a 1996 Ford Bronco, going 65 MPH, and there's a light North-Northwest crosswind of about 5 MPH. The road is wet because of a slight drizzle, and it's 4:30 PM local time, and 53 degrees Fahrenheit.

Phil: Okay! I slam into the rear quarter-panel of the car while breaking hard-left so I can send them into a spin!




Yeesh... I need a life.

 

[Impeesa]

Momentum is conserved. It is a linear relationship, so assuming roughly equal mass (which they do tell you to account for), simply adding the velocities works fine. Make one negative and you'll have a pretty good approximation of the final speed of the system, too. Now, for all the people spouting the kinetic energy formula... energy is conserved too... but much of it is released as sound and possibly heat. So that's really irrelevant, there's no accurate way to model that.

--Impeesa--

 

[Suldulin]

[edit: nevermind]

 

[Blacksad]

Momentum is conserved. It is a linear relationship, so assuming roughly equal mass (which they do tell you to account for), simply adding the velocities works fine. Make one negative and you'll have a pretty good approximation of the final speed of the system, too. Now, for all the people spouting the kinetic energy formula... energy is conserved too... but much of it is released as sound and possibly heat. So that's really irrelevant, there's no accurate way to model that.

--Impeesa--

It's a shock, so the Energy doesn't have the time to be immediatly released in heat or anything else at first, the kinetic energy is a good approximation in this case.

Originally posted by Castellan
I think a lot of people might have missed the URL in my original post. Go to http://www.farmingdale.edu/~kramerp...er/head-on.html abd check out the well-written explanation why the CoC rules are wrong.

I haven't missed it, but it's inaccurate.

let say you go from 200m/s to 50m/s in 1s, it's effectivly a 150m/s*s acceleration, and you continue to go forward.

let say you go from 50m/s to -50m/s in 1s, it's effectivly a 100m/s*s acceleration, and you go backward.

the first acceleration is the worst to the human body. the link you gave say the opposite. also it use a wall as the innert object and not a car of similar mass in the example, so it tends to modify the results.
[edit]
ie if the wall is elastic the car will keep all the energy if it is plastic (I don't know if it is the correct term in english), half of the energy will be released in the wall.
[/edit]

and yes I agree that a simple rule is better than an equation, but when a simple rule can be used to reflect reality, I feel it is better.