Quick question for the lorry drivers

Pants · 4 Mar 2008 at 19:07

therealnerd2 said:
Ahh crp, I got owned. Maybe you should try rolling down the hill yourself to just make sure eh?

I think that would be even slower. I would get dizzy before the bottom.

Scania · 4 Mar 2008 at 19:09

This thread is comedy, when I've stopped laughing, I may post a proper reply.

4T5 · 4 Mar 2008 at 19:15

Wang said:
Erm, as long as all external forces are the same, so say it is 2 identical lorries with one full trailer and one empty trailer, they will go at the same speed.

Pants said:
Err.... the heavier item will roll down a hill faster... lol.

For example. My bike rolls down a hill at about 30 mph. My car will roll down that hill much faster.

Quoted for Hilarity, posterity & the Sheer hell of a damn good

Wang · 4 Mar 2008 at 19:29

malc30 said:
Quoted for Hilarity, posterity & the Sheer hell of a damn good

Feel free to prove otherwise and i will be happy to admit i am wrong, just that as i remember from my Physics and Maths lessons at college, assuming all other variables are equal, then the mass of an object has no bearing on its acceleration. F=ma etc. The heavier truck will be coming down the hill at the same speed, just with a greater force.

Phate · 4 Mar 2008 at 19:32

[TW]Fox;11228505 said:
No.

malc30 said:
So a 70 tonne loaded lorry will go down a hill the same speed as an empty lorry will it
Motors has brought me the laughs lately.

I should really stop posting at work when in a rush

4T5 · 4 Mar 2008 at 19:34

Wang said:
Feel free to prove otherwise and i will be happy to admit i am wrong, just that as i remember from my Physics and Maths lessons at college, assuming all other variables are equal, then the mass of an object has no bearing on its acceleration. F=ma etc. The heavier truck will be coming down the hill at the same speed, just with a greater force.

Ok.
We are talking accelarating at 56mph & that is the Only clue you're getting.

georges · 4 Mar 2008 at 19:35

Wang said:
Feel free to prove otherwise and i will be happy to admit i am wrong, just that as i remember from my Physics and Maths lessons at college, assuming all other variables are equal, then the mass of an object has no bearing on its acceleration. F=ma etc. The heavier truck will be coming down the hill at the same speed, just with a greater force.

This man is right. When the only force acting is mavity, and given the truck is rolling down the hill >56mph therefore the engine is providing no force, the two trucks will accelerate identically. Of course there are other factors, such as the extra mass reducing the effect of wind resistance, but it also creates more friction so this will probably negate that.
This is pretty basic physics.

Uphill it's a different story, since F/m = a, so a similar powered engine, with less mass will accelerate more.

Downhill, with no engine force, they'll go accelerate at the same rate.

http://en.wikipedia.org/wiki/Gravitational_acceleration

In the absence of any other forces, any object will accelerate in a gravitational field at the same rate, regardless of the mass of the object.

Obviously there are other forces, but I'd imagine they're negligible, and I don't think that's what you're all getting at anyway.

therealnerd2 · 4 Mar 2008 at 19:35

What's accelarating?

[TW]Fox · 4 Mar 2008 at 19:54

therealnerd2 said:
What's accelarating?

The truck.

therealnerd2 · 4 Mar 2008 at 19:58

[TW]Fox;11229605 said:
The truck.

It was me being a spelling pedant

norm · 4 Mar 2008 at 20:20

Who decided on 56mph being the speed limit for HGVs? Seems somewhat arbitrary.

Defcon5 · 4 Mar 2008 at 20:28

norm said:
Who decided on 56mph being the speed limit for HGVs? Seems somewhat arbitrary.

It will probably work out as a round number in Kph

norm · 4 Mar 2008 at 20:31

Indeed, it's a little over 90km/h. But it also came to me average stopping distance for a fully laden HGV might dictate it. And engines are more fuel economic around that speed.

helpimcrap · 4 Mar 2008 at 20:39

i'm giving this thread 5 stars. brilliant!

username · 4 Mar 2008 at 21:21

georges said:
This man is right. When the only force acting is mavity, and given the truck is rolling down the hill >56mph therefore the engine is providing no force, the two trucks will accelerate identically. Of course there are other factors, such as the extra mass reducing the effect of wind resistance, but it also creates more friction so this will probably negate that.
This is pretty basic physics.

Uphill it's a different story, since F/m = a, so a similar powered engine, with less mass will accelerate more.

Downhill, with no engine force, they'll go accelerate at the same rate.

http://en.wikipedia.org/wiki/Gravitational_acceleration

Obviously there are other forces, but I'd imagine they're negligible, and I don't think that's what you're all getting at anyway.

I don't know all the physics stuff so you may be right but I promise that my truck when fully loaded rolls down the hill quicker than the empty truck. It does it every single time too. I think you are allowing too much force for increased friction. The difference between an empty and fully loaded truck is huge. I drive a class 2 (in old trucker language). When empty it weighs about 12tonnes. When fully loaded it can weigh 26tonnes. Twice the weight does a hell of a lot of overcoming of wind resistance and friction hence the increase in speed.

Trust me on paper it might be incorrect but thousands of hairy ar5ed truckers will tell you otherwise.

Psycrow · 4 Mar 2008 at 23:14

The trucks aren't sitting in a vacum and its a cubed relationship between velocity and force in air. The heavier truck, rolling down a hill will go faster due to its ability to overcome air resistance thanks to more energy.

If both trucks were having a race on the moon or something then it would be a different story.

Wang · 4 Mar 2008 at 23:19

malc30 said:
Ok.
We are talking accelarating at 56mph & that is the Only clue you're getting.

Only clue for what? And how are you accelerating at 56mph if it is limited to 56? Surely at this point acceleration is zero. All i ask is to explain the physics behind your statement.

georges said:
This man is right. When the only force acting is mavity, and given the truck is rolling down the hill >56mph therefore the engine is providing no force, the two trucks will accelerate identically. Of course there are other factors, such as the extra mass reducing the effect of wind resistance, but it also creates more friction so this will probably negate that.
This is pretty basic physics.

Uphill it's a different story, since F/m = a, so a similar powered engine, with less mass will accelerate more.

Downhill, with no engine force, they'll go accelerate at the same rate.

http://en.wikipedia.org/wiki/Gravitational_acceleration

Quote:
In the absence of any other forces, any object will accelerate in a gravitational field at the same rate, regardless of the mass of the object.

Obviously there are other forces, but I'd imagine they're negligible, and I don't think that's what you're all getting at anyway.

Agreed, exactly as i was thinking, i was doubting myself as people seemed so confident otherwise. But it is pretty basics Physics.

inferno · 4 Mar 2008 at 23:28

No way, you are wrong, heavier truck will roll faster. Just like a heavier ball falls faster that a lighter ball. In school physics we disregard air resistance!

Scuzi · 4 Mar 2008 at 23:29

Psycrow said:
The trucks aren't sitting in a vacum and its a cubed relationship between velocity and force in air. The heavier truck, rolling down a hill will go faster due to its ability to overcome air resistance thanks to more energy.

If both trucks were having a race on the moon or something then it would be a different story.

Correct.

[TW]Fox · 4 Mar 2008 at 23:30

Wang said:
Only clue for what? And how are you accelerating at 56mph if it is limited to 56?

Becuase the vehicle is going down a hill and thus doesn't need its limited engine to accelerate above 56mph.