I have consistently included the earth, but admit to being unsure of how much momentum could be lost to that, and what the limiting factors might be.
Ignoring the engine braking, what you seem to be suggesting is that it would be impossible to accelerate a trailer at the same rate (of the order of 1g) by pulling on it with a mbuttively powerful tractor unit, because it was so stuck to the earth by its tyres that you were effectively trying to drag an 8000km diameter lump of mostly-molten rock with it ? Doesn't that seem unlikely ? Sure, clamp the trailer brakes on and you can give the lorry an almighty thump and not get much forward velocity as a result, but that's not the case we're debating here.
Just by way of another data point, we are arguing about two vehicles with a relative mbutt ratio of 20:1. Something of the order of 20 times less mbuttive than the average car is the average human being. If you ran an Olympic athlete, weighing 12 stone, at 20mph into the back of a stationary car, without letting him bounce off, but instead made him sufficiently squidgy that he crumpled over the boot, how likely is it that someone inside the car only just managed to notice the impact ? (Ignoring stiction, which is far more resistant than rolling friction.) Momentum transfer to the heavier object is independent of actual velocities, just velocity differences, if my sums are correct. Would a car impacting a stationary lorry at 20mph (brakes off) also fail to rouse the driver ?
northern drivers....the worst 5271Mark Foster Having driven into Manc-Salford everyday for the last 3 years, that is a given. Manchester rules of the road. A red traffic...
I too would admit that a 40mph closing speed with no apparent effect on the lorry driver sounds unlikely. My only "experience" of this is that my father once rear-ended a lorry when he hit some ice under braking. The lorry was at a virtual standstill and the driver was only just aware of the impact. But from the damage to the car, I'd estimate the impact speed was maybe only 5mph. I wasn't in the car at the time - just saw the crumpled bonnet afterwards.
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Cruise Control dangerous 5270Nope, there have been numerous incidents of cars running into stationary lorries and the lorry driver not being aware. Even a vehicle with a lesser...
