Reel Physics: xXx: State of the Union - Riding the Rails

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I forgot about this movie.
I never watched it because I was sad there was no Diesel in it.

You know, I love it when some absurd ass stunt turns out to be plausible, at least mathematically.

4RT1LL3RY:

Are you sure about width being 68"? The important measurement you would be looking at is the wheel track, that gives the distance between the wheels on an axle from the hub. For The Cobra Concept the listed wheel track is 60.6" for the front and 60.4" for the rear. These measurements are from hub to hub so there will be rim to both sides of that measurement. The wheel size listed for the Cobra Concept are 10x18 for the front and 13x19 for the rear. From looking at the images available of the car you can see that the wheels are not centered under the vehicle, but mostly tucked under neither it.

With the 9.5" width rims used with the front tires you could have the front-wheels centered on the hub, from images of the rims you can see they are actually mounted with a bias toward the cars center-line. Even with a centered rim the front wheels will have a distance between them of 60.6" - 2*(4.5") giving us 51.6" between the edge of the rims. this is well within a reasonable bound for this theoretical vehicle on the rails. The rear wheels are more then wide enough to accommodate a rim.

Using the right measurements when doing the math makes it much easier.

TLDR; yes the vehicle would be able to fit properly on rails.

Metal to Metal friction varies less then other substances for sliding friction. For instance they used .61 as there coefficient of friction so the materials they compared using are Aluminium and Mild Steel. The sliding coefficient of friction between dry aluminum and mild steel is .47. Substituting .47 for .61 when calculating the Frictional force you get 3212.22 N, or 722.13 lb of force. That is still enough frictional force to reach 160+ mph.

I love you. I just wanted you to know that Arty.

Top Gear pretty much answered everything you need to know about the subject.

Back to the future... kind of...

4RT1LL3RY:

Metal to Metal friction varies less then other substances for sliding friction. For instance they used .61 as there coefficient of friction so the materials they compared using are Aluminium and Mild Steel. The sliding coefficient of friction between dry aluminum and mild steel is .47. Substituting .47 for .61 when calculating the Frictional force you get 3212.22 N, or 722.13 lb of force. That is still enough frictional force to reach 160+ mph.

Coefficient of Friction table

MUCH better. however the kinetic coefficient is still enough, rather amazingly so with the thermal traction gained from friction and the alignment basically playing ball
we have a winner, it's totally legit. fantastic.

that'd be pretty awesome a super high speed rail track for cars, i want one!

Wait, so was this one dubbed actually possible? (With a couple of liberties)

image

ReelPhysics:
xXx: State of the Union - Riding the Rails

Hop in the backseat with Colby and Jason as they find out if you can indeed ride the rails.

Watch Video

Quite possibly one of my favorite ones thus far guys, keep up the awesome work! By the way, was Colby eating some Lay's WOW chips that day? You know they cause anal leakage right?

4RT1LL3RY:

Lord Hosk:

Anakinnnn:

We gave them credit on that. Of course train tracks are not equal to almost any vehicle wheel spacing... but we just figured most everyone knew that. You also can't stand up in a car going 160mph and can't violently turn at that speed either. What we find interesting in scenes is getting down to the stuff that really is calculable... and not the stuff that we consider common knowledge. If we were a more mainstream show, we might have to dumb it down I guess and actually spell out all the problems with a scene... but, hey.... THIS IS THE ESCAPIST COMMUNITY!! ;)

Jason Dean
REEL PHYSICS

I wasnt saying "bad reel physics people you missed something crucial!" I was just suggesting that since you covered other "ok lets just say this is possible" like the tires blowing out perfectly and the insane turn, that you might have missed the wheel base thing which is not insignificant, although clearly less significant than the turn.

Are you sure about width being 68"? The important measurement you would be looking at is the wheel track, that gives the distance between the wheels on an axle from the hub. For The Cobra Concept the listed wheel track is 60.6" for the front and 60.4" for the rear. These measurements are from hub to hub so there will be rim to both sides of that measurement. The wheel size listed for the Cobra Concept are 10x18 for the front and 13x19 for the rear. From looking at the images available of the car you can see that the wheels are not centered under the vehicle, but mostly tucked under neither it.
image
With the 9.5" width rims used with the front tires you could have the front-wheels centered on the hub, from images of the rims you can see they are actually mounted with a bias toward the cars center-line. Even with a centered rim the front wheels will have a distance between them of 60.6" - 2*(4.5") giving us 51.6" between the edge of the rims. this is well within a reasonable bound for this theoretical vehicle on the rails. The rear wheels are more then wide enough to accommodate a rim.

Using the right measurements when doing the math makes it much easier.

TLDR; yes the vehicle would be able to fit properly on rails.

Metal to Metal friction varies less then other substances for sliding friction. For instance they used .61 as there coefficient of friction so the materials they compared using are Aluminium and Mild Steel. The sliding coefficient of friction between dry aluminum and mild steel is .47. Substituting .47 for .61 when calculating the Frictional force you get 3212.22 N, or 722.13 lb of force. That is still enough frictional force to reach 160+ mph.

Coefficient of Friction table

Did you take into account the left over horsepower and the potential torque of the drive train? If XXX was to hit the gas too hard he would lose traction almost immediately and start to lose speed. Of course I suppose since he was a secret agent super spy he could probably keep the car's power under control, so this is probably negligible.

Someone make a gif of them in the car.

Guffe:
Hilarious episode ones again xD
Loved the part with you guys inserting yourselves into the back of the car :D

Would it be possible to try and figure out if a bullet that's beeing sliced in half, by a sword (several movies do this), if the halves then fly past the head on each side?
I think I saw a video on TV in some crazy stunt show or something where someone sliced a bullet, with a sword, that went past him but that didn't cover how wide the bullet pieces then flew from each other...

This, every time I see a scene like that, I start wondering how slicing a bullet would affect its trajectory.
If I remember correctly, most guns put a spin on the bullets, I assume the sword puts a stop to that, and through elasticity might even invert it, and/or change the flight path with the bullet pushing itself away from the sword?
And how does a half-bullet behave in flight?

If it is not enough to make the halves miss the head, how does the angle of the edge (how "pointy" the sword is, should be arctan( (swords_widest_width/2) / sword_lengthto_widest )*2 ) affect the result, and what would be needed to push them far enough of their path?

And as a side question, what kind of edge would be needed for a bullet to actually slice itself, and what would the angle be when its actually enough to instead [i]block[/]?

barbzilla:

Did you take into account the left over horsepower and the potential torque of the drive train? If XXX was to hit the gas too hard he would lose traction almost immediately and start to lose speed. Of course I suppose since he was a secret agent super spy he could probably keep the car's power under control, so this is probably negligible.

That is the thing though. It doesn't matter if the wheels are spinning, there is still more then enough frictional force. .47 is the coefficent of kinetic friction of aluminum on mild-steel, (metal slipping on other metal).

And as Lugz said...

The Lugz:

MUCH better. however the kinetic coefficient is still enough, rather amazingly so with the thermal traction gained from friction and the alignment basically playing ball
we have a winner, it's totally legit. fantastic.

that'd be pretty awesome a super high speed rail track for cars, i want one!

So as the rims heat up the coefficient of friction will increase. Also its not hard to tell when your vehicle is slipping. The 2004 Cobra Concept lacked things like Anti-lock brakes, so its a safe assumption that it didn't have Traction-control either. On the Other hand the Cobra Concept shown at the show was electronically limited to 100mph.

Losing grip from wheel spin doesn't make you slow down, exceeding the limits of acceleration of the tire, aka wheel spin, just means you will accelerate slower than if you weren't spinning your tires. Keeping a cars power under control is fairly easy with any experience on icy roads or slick conditions. Except on a rail road you will have much more grip and still have about half the grip as you would on a regular road.

4RT1LL3RY:

barbzilla:

Did you take into account the left over horsepower and the potential torque of the drive train? If XXX was to hit the gas too hard he would lose traction almost immediately and start to lose speed. Of course I suppose since he was a secret agent super spy he could probably keep the car's power under control, so this is probably negligible.

That is the thing though. It doesn't matter if the wheels are spinning, there is still more then enough frictional force. .47 is the coefficent of kinetic friction of aluminum on mild-steel, (metal slipping on other metal).

And as Lugz said...

The Lugz:

MUCH better. however the kinetic coefficient is still enough, rather amazingly so with the thermal traction gained from friction and the alignment basically playing ball
we have a winner, it's totally legit. fantastic.

that'd be pretty awesome a super high speed rail track for cars, i want one!

So as the rims heat up the coefficient of friction will increase. Also its not hard to tell when your vehicle is slipping. The 2004 Cobra Concept lacked things like Anti-lock brakes, so its a safe assumption that it didn't have Traction-control either. On the Other hand the Cobra Concept shown at the show was electronically limited to 100mph.

Losing grip from wheel spin doesn't make you slow down, exceeding the limits of acceleration of the tire, aka wheel spin, just means you will accelerate slower than if you weren't spinning your tires. Keeping a cars power under control is fairly easy with any experience on icy roads or slick conditions. Except on a rail road you will have much more grip and still have about half the grip as you would on a regular road.

I'm sorry, I should have been a bit more clear. When you start slipping due to loss of traction you can't hold the accelerator down, you have to let off the gas and either pump the brakes or the gas until you can match it up and catch traction again, so you lose speed. Even if you held the accelerator you would lose speed though, unless you had enough power to continue to counteract the negative forces. This is like when you hydroplane, you lose traction, and until you regain it you will lose speed, but if you hold the accelerator you will lose momentum slower. As far as being able to feel the slip, that is why I brought up that he is a secret agent and he would be able to handle his car well enough (especially after the unbelievable tire blow to get on the tracks in the first place.

Quick Edit: looking at the friction coefficient you are right, they wouldn't lose speed. He would lose a bit of acceleration pumping the gas though. So I concede the point since he is a super spy.

performance seems a little stiff love the show but I wish they would relax more and have the jokes come more naturally.
hope to see more

American Fox:
Someone make a gif of them in the car.

image

Here you go!

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