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Comment by patrickg_zill | Hacker News Reader

I think the write-up is pretty good.

I would only point that 25 tons of force, isn't really a lot - I mean, the small jack that you use to lift your car can be a 5 or 6 ton device.

You have a vehicle traveling a decent rate of speed, for it to strike or run over anything at all will involve tons of force.

Neat explanation of the sort of math involved, with both SI and US units http://hyperphysics.phy-astr.gsu.edu/hbase/carcr.html . In the example, a car going 30 mph (50km/h) striking a tree will hit with about 48 tons of force.

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> I would only point that 25 tons of force, isn't really a lot - I mean, the small jack that you use to lift your car can be a 5 or 6 ton device.

Floor jacks easily punch through most points on modern cars. In fact, the only place that it is safe to jack up your car are special jack points which are reenforced to bear the load of the jack. The center ones on my car are pretty annoying to get to. Also, your estimate for the ratings of jacks is off by a factor of x2 to x4. Floor jacks, which have a leaver and a hydraulic component, are typically only rated for 2 to 3 tons. Scissor jacks, a manual jack that comes with your spare tire, are typically only rated at 1.5 tons or less.

> I would only point that 25 tons of force, isn't really a lot - I mean, the small jack that you use to lift your car can be a 5 or 6 ton device.

It's not clear to me why you'd say it's not a lot of force while making the comparison to a jack. Take a jack and use it under the wrong spot on a vehicle and you might get a pretty painful display of vehicle penetration, which is what we're really talking about here.

....yet the jack produces 1/5th the amount of force.

Just to put it into explicit perspective.

In both examples that you provided, the cross-sectional area over which the force is applied is greater, so the overall pressure is lower. The magnitude of the force applied isn't the only parameter by which to judge the structural integrity in this particular instance.

I think the rare occurance is not a collision with > 25 tons of force, but an upwards force on the underside of the car by an object capable of piercing 1/4 inch plate steel (and not ricocheting, as I suspect most debris would).

A jack, although maybe rated to 5 tons, is unable to pierce the bottom of my car at 25 tones of force because my car only weighs 1.5 tons. I'd have to run over something at speed that angles upwards after I drive over it, or drop my car onto something sharp (at 35km/h) to achieve a similar force.

I am quite sure much of the driving public never would have thought a battery powered car could go up in flames. That might be the real damage here.

Regardless of Musk's statement, a gasoline powered car would not have suffered a fire most likely in this incident as its fuel source does not stretch to the front of the vehicle. More than likely the debris would have done some serious damage to the underside of the car, if any. There is a lot of open, hollow, space in the underside of most modern cars.

He is handling it wrong by trying to tell people that this car fire is not anything special. Seeing that the fire department had to do quite a bit to contain it means his cars will burn to the ground just like any gasoline car will. I doubt any fire will leave the car in any state but salvage.

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