Three or so weeks ago, I was stuck in 65-mph traffic behind a flat-bed tractor-trailer carrying enormous spools of metal that were probably 8 feet in diameter and weighed a good 2-3 tons each. They were strapped in a vertical position (on their side) on the truck. The tie-down straps looked seriously undersized, yet I couldn’t pass the truck, so I started thinking of accident scenarios.
Question: Let’s say some cargo (steel I-beams or aluminum ingots or pallet of gypsum board) fell from a truck. Is an automobile always able, under normal driving conditions, to stop faster than the falling cargo, to avoid getting hit? Assume that one’s reactions are fast and accurately calibrated, and that one sees the cargo about to fall. Assume a dry, level highway and both vehicles are moving at say 70 mph.
Is there any object that can come to a rest faster than a breaking automobile? Wouldn’t most any falling cargo roll somewhat, due to angular momentum?
Well, at the moment it leaves the truck the cargo is traveling slightly less than 70 miles per hour. If it’s a giant ball of yarn you probably won’t have a problem stopping in time because you will be braking and it won’t be and will merrily roll downhill.
If it’s something that will stop very quickly due to mass/surface area, like say a crate of anvils, I’d say dodge, don’t try to stop in time.
Impossible to answer, unless we know the following distance of the second car.
From experience I can tell you that I have been able to stop / swerve when shit came off trucks in front of me. But I also allow more following distance than most people.
Once we establish the following distance, then we have to know what car the following car is. Brake capacity very greatly between different cars.
It just depends what falls off and how it lands. A modern car with ABS is extremely good at stopping quickly. It rests on four rubber devices specifically designed for gripping a road. It has special devices attached to each designed to be able to exert maximum stopping force without breaking traction.
Most random things that might fall off a truck are not going to be surfaced in grippy rubber, and even if they are, they are going to hit and roll, negating whatever grippy surface they might have. Even groman’s crate of anvils is going to crash and roll down the road, not land flat and skid to a stop. Even if it does land flat and skid to a stop, wood slides better than rubber tyres with modern ABS brakes attached.
I wouldn’t say it is impossible to imagine something that might be wide and flat enough not to roll, and surfaced with something that might grip and stop very fast, but I think that would be very much the exception.
Right, anything that can stop before you can will have to be stickier than the rubber on your tires. (Maximum stopping force is the product of the coefficient of friction for the object’s material and the normal force it exerts on the road).
Also, I’d imagine any heavy objects that manage to penetrate and deform the asphalt or dig themselves in in some manner could also stop faster than you.
That said, human response times are highly variable, ranging from 200-400 ms in a “lab setting,” but out on the road where you might be tired, talking, distracted by screwing with your radio, etc. they could be up to a second or longer.
Point being: don’t risk it. Allow for an appropriate follow distance.
Purely anecdotal evidence. I was behind a flatbed truck a few years ago (one of those designed for carrying other vehicles, with a sloped back) that had a large box of something sitting on it. The box was unsecured and every time the truck would bounce (it was empty other than this box) the box would bounce a few inches back. I was in fairly heavy traffic (though moving well) and so I just backed off a respectable distance.
Eventually what I was expecting happened. The box bounced back onto the sloped rear of the trailer and slid down it onto the road. I was able to brake, signal and change lanes before reaching the box, which was still sliding along the road as I passed it.
If I hadn’t been able to change lanes I’m confident that I would have been able to stop before hitting the box though I will repeat that I saw what was happening and had backed off from the truck before it fell. If I had been following at standard Atlanta traffic distance (20 feet at 80 mph) then it might have been a different story.
The answer to the OP is no. Just picture a huge block of playdough fallng off a truck, or a block of silly putty, which is similar but would have a higher coeficient of friction. ABS and the right tires do a remarkably good job of bringing a three-thousand mass mounted on wheels to a stop, but there are many objects that would come to a stop quicker.
How about you name one that actually might fall off a truck in the real world? I dunno about you, but I haven’t seen too many giant blocks of Pla Doh or Silly Putty trucking down the interstate lately.
I suppose a factor I hadn’t considered was weight. I suppose if a big flat box with rubber feet filled with, umm, a cello in packing foam might have such a good friction to weight ratio that it might stop pretty quickly. But then something with those sorts of characteristics probably isn’t going to do too much damage to you when you hit it, either.
Wait, that doesn’t make sense. Normal force is mg, and momentum is mv. G is 9.8 m/s[sup]2[/sup], and V is ~31 m/s. There’s no way normal force could be greater than momentum.
Sounds like you should move to a happier place. How about: A bag of fertilizer, dog food, sand. A bag of coffee, tea, sugar, flour, salt. A magazine. A carton of milk. A bean bag chair. A crate of grapes. A folded-up quilt. A down pillow. A bag of clothes going to Goodwill. A box of clothes. A rug. A rack of clothes. A package of chopmeat. A case of bottled water. A dead chicken. A bag of charcoal briquettes. A sofa. A box of books. A palette of olive oil. A tree with the ball attached. I’d even bet: a full sheet of sheetrock. And, of course, a rube.
You are about 0.7 second behind the truck (70MPH = 102.6feet/second) Tailgating like that, I am going to assume unless you are very lucky, and paying a lot of attention, you will hit the object.
Most of these things are going to roll. All the boxed and bagged things will. None of them are comparable to a big blob of play doh. Some of the very light and un-aerodynamic things like folded up quilts are going to stop fairly quickly but they are in the “so light they don’t matter” category.
A pallet of bricks is going to smash apart and the bricks are going to slide along for quite some distance. There’s nothing magical about them that’s going to make them stop suddenly.
