Carryfast:
Buckstones:
Carryfast:
Gembo:
If those coils are 10 ton each, how much force do they have at 40 MPH? A lot more than 10 ton.^ This is the question in contention.The scientists seem to think that it’s all about the relative speed between the load and truck.According to them so long as that relative speed is kept to zero then all they need to do is apply an opposite 1g pull,or even less with a bit more friction against the load bed,to cancel out all of the kinetic energy contained within the 40 mph load which sounds like bollox to me.That’s even without factoring in any potential shear loadings against the straps by the load.
IE their whole case is that a 10t + lump of metal travelling at 40 mph contains no kinetic energy at all,so long as it’s supposedly stopped from moving relative to the load bed,by supposedly applying an opposing pull equal to its static gravitational weight.
Which seems to defy all the laws of kinetics to me.
The laws of kinetics simply say Energy = Mass x (Velocity squared) divided by 2, Momentum (not Corbyn’s mates)
= Mass x Velocity.
These apply to the entire vehicle and its load, the issue of restraining the load (as for passengers with seatbelts) is purely what force is necessary to keep the load in place under a deceleration of the whole vehicle.I never said the load had no kinetic energy, I used Newton’s Law of Force = Mass x Acceleration, from which one g of deceleration or acceleration will cause a mass to exert a force equal to its weight.
That is why you weigh what you do, and astronauts weigh nothing.Great so we put a 10t + steel coil in the cargo hold of the space station with no straps on it at all then we reduce orbital velocity for a lower orbit and the thing will just stay there and not punch its way through the side because it weighs nothing ?.
Or we fire an 88 mm anti tank shell at the armour of a Sherman it will just stop and fall to the floor and do no damage when it hits the side because at that point it’s lost its velocity and is travelling at the same speed as the tank.As opposed to the laws of kinetics in which both the mass and the velocity subject the formula are exchanged for energy which just smashes and/or melts the armour.
On that note if you agree the 10t + load retains its kinetic energy,that being 40 mph’s worth in the case of the truck load and anyone’s guess in the case of the space station.How can you then only rate the load security based on 1 g of deceleration only supposedly exerting a force on anything in its way that’s only equal to its static weight.
When surely at least some of the formula should be based on the laws of kinetics and inertia.
On that note I’d guess that a race car 4 way safety belt system and anchorages or for that matter even a standard car system has a lot more strength than just that needed to suspend the static weight of a person above the floor ?.
OK. Taking the earth as our datum. A lump will have a kinetic energy relative to the square of it’s speed. Our ten ton lump has 4 times the energy at 40 kph as it does at 20 kph. Our truck as a whole has 4 times the energy at 40 kph as at 20 kph. All good. So our brakes need to dissipate 4 times the energy from 40 as from 20. (Thats why sports motorcycles have huge brakes, not because they’re heavy but because they’re very fast). That is all true.
But it is a but of a red herring.
We can see that our truck will not decelerate st more than 1g. (We’re ignoring aerodynamics as we’re not going too quick and have no spoilers). We are being slowed by brakes but our deceleration is decided by the amount of grip we have. With normal tyres on a dry road we’ll have a coefficient of friction of 1.0 at max.
So friction (the grip we have on the road) is the limiting factor. Out truck, call it 20 tons is pushing down (weighs) 20 tons and so (mu=1.0) receives a ‘pull’ from the road of 20 tons. In order for the 10 ton load to slow down at 1g too, that must receive a 10 ton pull. Assuming no headboard etc, that pull comes from the friction between load and bed. If we have mu of less than 1 we need straps or chains to ‘push’ that lump harder onto the bed.
The speed of the vehicle doesn’t affect the amount of FORCE to stop it, for any given rate of speed change. However you are correct the speed does affect the amount of ENERGY we need to get rid of. Stopping from 40 will get our brakes 4 times as hot, as from a stop from 20.
I’m confident that’s all correct. And I’m equally confident that I’ll never be asked to write a textbook.
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