We were talking about carrying a load. We have to make sure the load is safe. The biggest force a hgv truck produces under breaking is 0.8 going forwards. does this seem correct?chrishgv said:Hi guys I'm a truck driver. Not sure if I'm posting in the right place so i apologise. Iv'e been on a course today about trucks. The course leader was talking about forces. A trucks force forwards can be 0.8. Is this true?
This is probably correct . My real questioning is when he said that.. Because people get whiplash. There is a force pushing backwards when you break hard. He says a pallet on the truck will move backwards after a crash?chrishgv said:We were talking about carrying a load. We have to make sure the load is safe. The biggest force a hgv truck produces under breaking is 0.8 going forwards. does this seem correct?
A truck’s force certainly could be 0.8 in some units. Are you familiar with the concept of units? Like distances can be measured in inches or miles or meters. Forces are usually measures in Newtons or pounds (pounds can be confusing because it is sometimes a unit of force and sometimes a unit of mass and so context is needed)chrishgv said:A trucks force forwards can be 0.8. Is this true?
For those of us in the U.S., a "HGV" truck is a Heavy Goods truck. Which is what we would call an "18 wheeler" or a "semi-trailer truck".chrishgv said:We were talking about carrying a load. We have to make sure the load is safe. The biggest force a hgv truck produces under breaking is 0.8 going forwards. does this seem correct?
Iv'e had a drink. Bare with me. On the course he says there is a force pushing backwards after a crash. He references whiplash. If a pallet off bricks was moving forward on the wagon during a crash. could a force push it backwards afterwards?Dale said:A truck’s force certainly could be 0.8 in some units. Are you familiar with the concept of units? Like distances can be measured in inches or miles or meters. Forces are usually measures in Newtons or pounds (pounds can be confusing because it is sometimes a unit of force and sometimes a unit of mass and so context is needed)
For a frontal collision I can’t envision how it could happen. For a rear end collision certainly the can happen.chrishgv said:Ok. After a collision. He is saying a pallet off bricks (anything) will move backwards after a crash. I this possible?
Can you explain the argument in detail?chrishgv said:Can i get any feedback to show how he is going wrong?
A frontal crash or a rear end crash?chrishgv said:the lorry crashes
he states there is a force pushing the pallet back? how is this possible? txchrishgv said:frontal crash. on his diagram after the crash the pallet has moved backwards in relation to the headboard of the truck.
When the truck crashes its acceleration is backwards (in the external inertial frame). So in the truck’s frame the inertial force is forwards. Relative to the truck the bricks will be accelerated forwards. There isn’t any rearward force on the bricks relative to the truck.chrishgv said:a lorry is traveling forward. a pallet of bricks is against the headboard of the trailer. the lorry crashes. after the crash the pallet of bricks moves backwards. he has an arrow on his chart showing the pallet moving backwards. he says for every action equal reaction. the pallet is moving backwards in his opinion.
You could get some bounce, perhaps -- the truck bounces from the wall and the brick pallet bounces from the front wall of its compartment. One would have to speculate about what components are elastic enough to provide much bounce. An argument on a basis of "equal and opposite reaction" sounds like vigorous handwavium.Dale said:When the truck crashes its acceleration is backwards (in the external inertial frame). So in the truck’s frame the inertial force is forwards. Relative to the truck the bricks will be accelerated forwards. There isn’t any rearward force on the bricks relative to the truck.
I'm assuming i was correct then? He's a good teacher. I'm here because i want to help him and his lessons. I'l give him this link tomorrowDale said:When the truck crashes its acceleration is backwards (in the external inertial frame). So in the truck’s frame the inertial force is forwards. Relative to the truck the bricks will be accelerated forwards. There isn’t any rearward force on the bricks relative to the truck.
From Wikipedia:chrishgv said:teacher mentions in his lesson that the head rest in a car is to stop whip lash. Am i right in thinking that you can only get whiplash from a rear end hit?
A WHIPS [Whiplash Protection System] equipped seat is designed so that the entire backrest helps to protect the front occupant's neck in a case of a rear impact.
No.chrishgv said:Am i right in thinking that you can only get whiplash from a rear end hit?
After the crash, possibly, due to the relaxation of elastic compression forces on the pallet from the bulkhead, or from the elastic compression properties of the contents within the pallet.chrishgv said:He says a pallet on the truck will move backwards after a crash?
All these scenarios seem to depend on a significant amount of resilience. A major part of vehicle design for dealing with collisions is permanent distortion of the structure to dissipate the energy. I can't think of any element of the tractor and trailer that might have longitudinal resilience, built in, except the driver's seat.256bits said:After the crash, possibly, due to the relaxation of elastic compression forces on the pallet from the bulkhead, or from the elastic compression properties of the contents within the pallet.
Sounds reasonable. I'd be curious as to what the greatest movement he's seen, is.chrishgv said:He says a pallet on the truck will move backwards after a crash?
Put the pallets on wheels, which they are not ( usually ) and the floor- pallet reduced friction would have interesting effects.sophiecentaur said:The only mechanism I could think of that could produce a backlash effect could be if the pallets were not secure and could carry on traveling forward after the trailer had stopped. They could then hit the inside front of the trailer and nudge it forward. That would cause the driver to feel a forward impulse.
Shifting loads are a real embarrassment. Even a pot pf paint in the back of your car can give serious grief if it's not secured. Some of what's described in this thread is very frame dependent and a lot of statements should be tidied up before they can be taken seriously. People 'feel themselves thrown forward' and that colours a lot of descriptions - from teachers as well as the general public.256bits said:Put the pallets on wheels, which they are not ( usually ) and the floor- pallet reduced friction would have interesting effects.
So would I. Elastic distortions would surely be a lot less than plastic, if there is any significant movement. The exception could be vertical 'bouncing' as suggested.hmmm27 said:I'd be curious as to what the greatest movement he's seen,
Ah, well... my assumptions are of an impact with a bridge abutment at suburban speeds ; also a straight-bed (2-5 ton) truck (amended to include a tractor-trailer, after I reread the thread) ; carrying, a pallet of bricks about 4'cubed (which turns out to be wrong : a pallet of bricks is only 5 bricks high, massing about 1.25t).sophiecentaur said:Shifting loads are a real embarrassment. Even a pot pf paint in the back of your car can give serious grief if it's not secured. Some of what's described in this thread is very frame dependent and a lot of statements should be tidied up before they can be taken seriously.
True, but - even though the effect is much less with a squat pallet (ie: low CoM) - I think it would still be significant enough to count.Elastic distortions would surely be a lot less than plastic, if there is any significant movement. The exception could be vertical 'bouncing' as suggested.
What component of the chassis / body would distort elastically? Vehicles are designed to suppress flexing because that affects behaviour with instantaneous loads (as with the collision and bumps in the road) `In collisions, the requirement is to absorb the energy and not to store it and deliver it back into the situation. Freak conditions can induce vertical motion (one vehicle ending up on top of another) but even that is dealt with by the barriers hung down from the tail of trucks.hmmm27 said:- I think it would still be significant enough to count.
