Nose weight too high
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and you MM appear to be either one of those posters that have to post on every single thread about something or feel intimidated by someone who has knowledge above yours?
If you don't like a thread don't read it?
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wow, OK just go back to one of my posts and point out the error in the maths?
for the record you are still saying that weight in front of the axle and not the CoM causes increased nose weight?
I'm not sure what a teacher's expectations are and how any other job exceeds them? or vice versa?
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Nothing magic. Everything shows up in Latest Activity.
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wonder why? well I suppose someone has to
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ah yes, the those that can nonsense, I think I asked you already, so everything you have ever been taught was by people who couldn't? Btw why am I an ex-teacher?
I think you may like the sound of your own voice too?
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but they still taught you, so couldn't they 'do' in the real world and had to turn to teaching?
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Quite so Jennyc. Forgetting any side effects like compression of springs if you add weight in front of the axle then the nose weight increases, as does the load on the axle of course and the C of G shifts towards the axle. Nevertheless you can consider the original C of G of the caravan as one mass then add a second mass forward of the axle and take moments about the axle (which is the fulcrum) then the additional moment added must result in a greater force upwards on the nose hitch to equalise the clockwise and anti-clockwise forces. Of course, the extra load has to be shared by nose wheel and axle (assuming no steadies down) and the proportion shared depends on where the weight is.
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sorry,you mean greater upward force = less downward force (nose weight) ?
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The downward force of the caravan weight is opposed by the ground’s upwards reaction on the wheels and nose wheel which is why you lift the nose up to hitch up. Sorry Corners, but moments are extremely simple if you take them around a fulcrum point like the axle. You can take them about any point like the C of G but then, when you add weight, you increase the counteracting force on the support points I.e. axle and nose. Therefore you have two equations and two unknowns instead of one simple one. Add 100 kg and you add two upward reactions on axle and nose without knowing how much on each.
I will give an extremely simple see-saw example when I get a "moment”. Sorry!
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you are still puncturing your own argument (those that can do, those that can't teach, its one or the other right) if you had teachers (and good ones) then they are in the 'can't' category as defined by your rule
Hey your the one that brought it up!
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I just wanted clarification on what you meant by greater upward force. Assuming the van is level (so we don't have to bring in trig) there are three forces acting on the van, weight acting through the CoM and two different reaction forces on the hitch and axle. I think you are saying that if you now add a weight between the CoM and axle the reaction force at the hitch increases?
Even taking moments about the axle (and as two equations doesn't scare me I always use the CoM and anyway you usually resolve the forces to help solve the styem), the weight of the van and added weight are anticlockwise moments, but the reaction force at the hitch (pointing upwards) is a clockwise moment. As it is in equilibrium the anti clockwise = clockwise moments
Reaction at hitch x distance from axle = weight of van at CoM x dist from axle + new weight x dist from axle
all correct?
wish CT had an equation editor?
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I've read but not commented on this thread....until now...
i don't have a teaching degree (although my daughter does) but am a pretty practical sort of person when it comes to physics and mechanics.
the post above describes what (I agree) will happen (in real life) and can easily be visualised using the seesaw image....
a seesaw is placed incorrectly on its fulcrum, with the centre of gravity off centre.....the seesaw tilts in that direction....
in order to level the seesaw, a force must be added to the opposite side of the fulcrum.
is anyone really saying that, if (for example) a person sat close to the fulcrum on the downward side (but not as far down as the COG) then, miraculously, the tilted seesaw would rise?
ive been on many seesaws in my life and have never seen this happen.
what happens in real life is that the tilted side hits the floor with a crash.
now, I'm not one to think that the world is flat, I've seen too much of it to know this isn't true....but caravan noses rising when a force is added to the nose wheel side of the axle.....? not something I've encountered.
im perfectly happy with Hitch and Jenny's position above which pretty much nails it....
the COG (ahead of the axle) does apply a turning force and loads the nose wheel....adding a further mass ahead of the axle adds a further turning force in the same direction, hence increasing the load on the nose wheel.
again, only my simplistic view based on logic (my original profession) and real world experience.....
im sorry Corners but you have failed to convince me (and many others it seems) of what you say is 'proof'......
anyone got a spare caravan and a nose weight scale?
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just been giving this some more thought in the shower....as you do...
we have a lot of farm trailers about at the moment and I tried to visualise this.....
a trailer is (say) 20' long, has its axle only 3' from the rear.
the trailer is empty, yet itsCOG, being (say)10' ahead of the axle is applying a turning moment downwards on the hitch (let's say it's resting on the ground)
the farmer comes along with his fork lift and starts loading up the trailer from the rear first, so bales go on, ahead of the axle but behind the COG....
now, if Corners is correct, the hitch will eventually rise into the air after sufficient bales have been added to counter the original force?
with a layout like this(used to illustrate the discussion) IMHO the only way the hitch could be lifted (not with the tractor) would be to add a massive load in the very rear of the trailer, just behind the axle.
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I’m afraid they Corners is trying to use Maths to demonstrate something that is clearly wrong. You don’t need to take moments to know that putting weight in front of the axle will increase the nose weight. I can see that I will have to tell my see-saw story and bore everybody. Sorry about that but I promise it will be easier to understand than the equations.
Corners - No. if you add weight between the hitch and the axle the reaction force on BOTH the nose wheel and the axle increase, in a ratio determined by where you place the load. It’s so much easier to take moments about a fulcrum because you eliminate one variable. Time for my see-saw story - later!
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is anyone really saying that, if (for example) a person sat close to the fulcrum on the downward side (but not as far down as the COG) then, miraculously, the tilted seesaw would rise.
I've not said that at all, it won't rise but I've said the 'the turning effect at one end will change, that's a big difference. Weights and turning can be added or taken away and that doesn't ways mean motion. You are sitting on your chair? Put a 2 litre bottle of water on your lap, you falling through the floor yet? No but the reaction from the floor has increased to compensate your added weight. place your book over the desk about three quarters? then put a pen on it on the end, does it turn?
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of course it won't rise....I was taking your position to the nth degree...
but, in my example with the trailer, are you saying the more bales loaded into the rear of the trailer, behind the COG but ahead of the axle, the less load there is on the hitch?
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This is my last post and I'm going to the post office to return the two degrees I've studied on this as they are clearly wrong. I'll also need to tell the exam boards that the question I've set like this were clearly wrong. Please post if you want but I won't see it
But none of you have corrected my maths I've noticed?
Anyway bye
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QED?
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Of course we’re all right. It has nothing to do with theories or facts but we’re all right because we do what suits each of us best.
That’s all there is to it so there’s no need for debate at all.
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Debate?😂😂😂. It was spatting in the schoolyard mostly☹️
DD’s last post was the most sense I’ve read👍🏻
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I love see-saws; they are such a good illustration of some very simple rules about moments and levers… and kids love them. They instinctively sit at the right point to balance their weight differences. Also, a see-saw is just like a caravan.
So I go to the local playground with my two mates Fred and Charlie (as you do). Both weigh 100 kg and Fred immediately sits half way down one side of the see-saw. I run around and pick up the end of the see-saw to make it horizontal again. Because Fred is halfway along I only feel 50kg (I exert an upward force of 50kg to counteract half of his weight). The other half of his weight is supported by the centre support which is beginning to creak (it is designed for kids). I am the hitch point, Fred is the caravan Centre of Mass and the centre support is the caravan axle.
Now Charlie jumps on the centre support (don’t do this at home). I feel nothing, but the support is now loaded to 150 kg (his full weight plus half of Fred’s). It’s beginning to strain! Charlie walks towards me and the weight I am holding starts to increase. He gets a quarter of the way along and I now have half Fred’s 50 kg plus a quarter of Charlie’s weight – 75kg. The good news is that the load on the support has gone down. Charlie reaches Fred and they embrace (it’s allowed these days). I am now carrying half of their combined weight i.e. 100 kg. The axle (centre support) is also carrying 100kg. I can just about manage but when they both jump up and down the dynamic load is too much and I drop the end of the see-saw. The Club’s Safety Department are investigating.
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Corners, this is daft. You asked why nobody has corrected your maths. OK, here goes.
Firstly you haven't indicated the downward mass of the caravan at point A (call it M).
Secondly, you have taken moments about the axle, P1, but you have included F1. F1 has no moment about the axle as it is at zero distance.
So, you could say that d1 x M = F2 x (d1 +d2) (as described in my see-saw story)
Then, if you add a weight M2 at a point d3 you get (d1 x M) + (d3 x M2) = (d1 +d2) x F2.
Personally I prefer the see-saw story.
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Note to OP........
We have seen the tail wagging the dog many times on motorways, a large, powerful car is always better. Driven carefully of course!
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, it must be all that up and down ......