Steel Slide. Sheet Steel in transport moving at high speed.

How much chain is too much?...

Answer, how much have you got?... and have you got any more?....
If in doubt, use another one.

Set off, brake sharply before you get out of the yard, if it moves at all, go get more chain.

Now you know as much as I do on that subject.

Except, if it moved, you dont have the experience I have, because NOTHING moves when I chain it down.....
I have seen most everything, but am willing to see just one more trick if you got it?...

a better myth would be that an kind of plate or sheet load will wander while in motion, unless properly secured down. - I am not sure steel will wander at highway speeds, but I can say for a fact that a stack of plywood will cheerfully play air-hockey at 60 MPH.

it has to do with deceleration rates.

take a test car collision. if the car has an 8 foot long crumple zone, and the collision is such that it uses all of the crumple zone; if the dummy is securely belted to the seat, then as soon as the car impacts the barrier, he will begin decelerating, and will decelerate from the test velocity to zero in approximately 8 feet. on the other hand, if he is unbelted, he will continue at the test velocity until he strikes the steering wheel, before he begins decelerating - so there is an initial impact with the steering wheel and then the more rapid deceleration over the shorter distance (because part of the crumple zone has already crumpled before he hit the steering wheel.)

or to use a different analog: you have two boxers. in test one, boxer one places his glove against boxer two's chin. in test two, he starts with his glove a foot back. in which test do you believe he will be able to hit boxer two harder?

I huess to spell out what I am saying - you are not measuring the force required to bring the load to a stop - you are measuring the force that the load applies to keeping the guard in motion, and with a space between the two, the difference in kinetic energy at impact is different, which means that the load is striking the guard with more force.

final analogy: if you are driving your car with a 1000# brakeless trailer hitched on, and make a panic braking, how much damage does it do to your car? then if you are driving your car with a plank in a 1000# car tailgating you and make a panic braking, how much damage does HE do to your car?

it is about relative velocities and collision forces.

with a proper load, the load and the guard are both going at the same speed on impact, so the interaction between them is more of a push with a space, the guard has already slowed down significantly before the load hits it, so it is a collision.

okay. take two trucks and put on a concrete roller - one chocked against the guard and one chocked a foot back from the guard.

run the truck into a barrier such that it crushes 2 feet of the truck before it all comes to a stop. - from 50 MPH.

truck 1, with the roller against the guard, will bring the roller to a stop in two feet. - when the force first hits the guard, the roller is going 50 MPH, and the guard is only marginally slower.

truck 2, with the roller a foot back from the guard, will have already crushed a foot of the cab before the roller hits the guard and begins to decelerate. the guard is now trying to bring the same roller to a stop from the same velocity, in ONE foot. when the roller hits the guard, the roller is still going 50 MPH, but the guard has already been decelerated to around 25 MPH.

addendum: I think it is a case of it being so simple, you're having trouble seeing it. if the load is against the guard, they are inertially coupled - in a collision, they stop as one. if the load is not against the guard, they are not coupled - and there is a collision between the load and the guard.

well, it has the commonality with a road roller that its working part is round. other than that, one is made of concrete and one is for pressing down asphalt.

again, I say to you, if a guy is going to punch you in the chin, is it going to hurt more if he starts with his fist against your chin or if he starts from a foot back? if you do a panic braking is it going to damage your bumper more if you have a brakeless trailer on your trailer hitch, or if you have a plank sending a text message from a foot behind you? when a karate demonstrator breaks a board, does he start with his hand on it, or does he pull it back? what is the commonality? the difference between a push and a hit.

if you take that road roller and set it so all the chains holding it back have a foot of slack in them, do you expect it will stop when it hits the end of them as well as it will stop if they are already drawn up tight? when you tow a stuck vehicle, do you draw the towline tight before you apply power, or do you leave slack in it?

take your bathroom scale and set a 20 pound box on it. read the scale. now lift the box 6 inches and drop it on the scale. what was the peak weight the scale showed?

if the load shifts forward and strikes the guard in a collision, it will deliver more kinetic energy than if it cannot take a running start at it. full stop. in short: it takes less strength to keep it from moving than to stop it once it starts. you KNOW this.

That is what I meant in case of the photographed STGO load above.(Crane in TLW's post)

If I drop a 20kg on a stationary set of scales, the scales are not moving.
If I drop a 20kg box attached to a set of scales, that is the readings that would make more sense, then dropping the box with a one inch gap between box and scales, and both are moving at the same speed, identical to the previous, and both have to stop with the same force, so why the difference in readings?...

I know.

Its because the scales will stop a micro-second before the box.

But why does that make a difference?... the only thing that has changed is time its self, or the time of events.
If you look at it in that way, it kind of infers that time has mass.
And that cant be right?...
Can it?...Brian Cox Physicist

And on that, if the time between impacts changes, from micro second to full second, how much difference is there in impact force?....

Is there a difference then between a load that is loosely leaning against the headboard, and one that is fixed there with bloody huge bolts.

Is there a difference in force between dropped objects under gravity and objects at the same speed travelling horizontal.

And if so, why?...

I know, I am a bloody nuisance with all these questions....
Anyone got a link to Brian Cox?....
(The Brits amongst us may get that one quicker....)


[edit, thats unfair, here, this is who he is... Brian Cox Physicist ]

let me try it another way - loading a load that has the potential to slide forward and not having it against the guard is like loading your truck and securing the load to your minimum satisfaction, then removing a tie down.

perhaps.

you should load cargo that has the potential to slip forward, against the cab guard for the same reason you should have all your tie downs secured tight. your cab guard is just another tie down, and not having it secure allows the load to start shifting. remember, it is not speed that does the damage - it is difference in speed.