# Braking force of a truck

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?

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?
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?

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?
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???

Dale
Mentor
2020 Award
A trucks force forwards can be 0.8. Is this true?
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
jbriggs444
Homework Helper
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?
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".

It is plausible that such a truck can brake at 0.8 gees of acceleration. This means that the carried goods can experience an apparent forward force equal to 0.8 times their weight.

Delta2, russ_watters and chrishgv
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)
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
Mentor
2020 Award
Collisions are pretty complicated with lots of things happening very quickly. Whiplash is usually associated with a rear end collision with an inadequate or poorly positioned headrest.

I could envision that during a frontal collision a pallet of bricks could slide forward to the cabin and essentially act as a rear end collision just moments after the original frontal collision. I don’t know any studies on it, but it seems plausible to me.

chrishgv
Ok. After a collision. He is saying a pallet off bricks (anything) will move backwards after a crash. I this possible?

Dale
Mentor
2020 Award
Ok. After a collision. He is saying a pallet off bricks (anything) will move backwards after a crash. I this possible?
For a frontal collision I can’t envision how it could happen. For a rear end collision certainly the can happen.

chrishgv
ok thank you. He's stating his theory on the basis of whiplash. It just seemed against the laws of physics to me. He teaches this class to 20 people a week. Can i get any feedback to show how he is going wrong?

Dale
Mentor
2020 Award
Can i get any feedback to show how he is going wrong?
Can you explain the argument in detail?

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.

Dale
Mentor
2020 Award
the lorry crashes
A frontal crash or a rear end crash?

frontal crash. on his diagram after the crash the pallet has moved backwards in relation to the headboard of the truck.

frontal crash. on his diagram after the crash the pallet has moved backwards in relation to the headboard of the truck.
he states there is a force pushing the pallet back? how is this possible? tx

I just can't see a point where the pallet has gone backwards

Dale
Mentor
2020 Award
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.
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
jbriggs444
Homework Helper
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.
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.

hmmm27, Dale and chrishgv
handwavium wow. waves hands. The guy is a great teacher.

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 tomorrow

Dale
il sober up before i post again. don't worry i'm not driving i'm on a course this week. feel free to add more for clarification.

just sobering up a bit and thinking about your answers. 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? I don't think he understands this. He thinks whip lash comes from the (recoil?)

nasu
Gold Member
Ask him what is the point of wearing sit belts. If you are pushed backwards during frontal collision, I mean.

jack action
Gold Member
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?
From Wikipedia:
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.

256bits
Gold Member
Am i right in thinking that you can only get whiplash from a rear end hit?
No.
More often, occurrences of whiplash are from a rear end, but half as many can be from frontal, and also from a side collision.