(Steven Shelikoff) wrote in message
Are you actually trying to say that if I have a boat/trailer that weighs
10,000 lbs and the hitch is 10' from the axle and the hitch weight is
1lb, then I add an extension on the end of the tongue to increase the
hitch to axle distance to 15' and the hitch extension weighs a million
pounds, that I have not changed the location of the cg of the
boat/trailer in relation to the fulcrum, which is the axle?

Yep, if you are not including the hitch in the calculations, then yes.
What YOU seem to have not included, which would make YOUR analysis
fatally flawed, is the fact that the fulcrum point is NOT the CG, and
ADDITIONALLY, you've done NOTHING about the fact that the fulcrum is a
long ways from the CG in the Z direction.

If that's what you're trying to say, then I can only reiterate my
original point, which is that it's amazing to me the lack of
understanding of simple physics from quite a few posters that this
thread has brought to light.

Steve

I agree. You don't have a clue.

On 12 Dec 2003 04:26:12 -0800, (basskisser) wrote:

(Steven Shelikoff) wrote in message
Are you actually trying to say that if I have a boat/trailer that weighs
10,000 lbs and the hitch is 10' from the axle and the hitch weight is
1lb, then I add an extension on the end of the tongue to increase the
hitch to axle distance to 15' and the hitch extension weighs a million
pounds, that I have not changed the location of the cg of the
boat/trailer in relation to the fulcrum, which is the axle?

Yep, if you are not including the hitch in the calculations, then yes.
What YOU seem to have not included, which would make YOUR analysis
fatally flawed, is the fact that the fulcrum point is NOT the CG, and

Of course not. As I said above, the fulcrum is the axle. The CG has to
be forward of the fulcrum for the hitch to weigh above 0. So now that
you understand that the fulcrum is at the axle and the CG is not at the
fulcrum, I'll ask you again:

When I said:
Bzzzzt! Wrong answer. It doesn't matter what a foot of the boat and
trailer weigh. The fact that it's wrong can be demonstrated very simply
by taking the problem to an extreme. Say in your example above that
your boat and trailer weighs 10,000 lbs and it's balanced so that the
hitch weight is only 1 lb. If you add 5' to the tongue, you are almost
gauranteed to *increase* the hitch weight unless you use some sort of
space aged material that weighs less then 1lb for the entire extension.

The boat and trailer could weight 1000 lbs/foot and you still would
significantly increase the hitch weight if the extension only weighed 1
lb/foot.

and you replied:
Uh, no...let's see if YOU want to play the game. Find in the above
where you are in HUGE error. Hint: The c.g. of the boat/trailer has
not changed in relation to the fulcrum.

Are you actually trying to say that if I have a boat/trailer that weighs
10,000 lbs and the hitch is 10' from the axle and the hitch weight is
1lb, then I add an extension on the end of the tongue to increase the
hitch to axle distance to 15' and the hitch extension weighs a million
pounds, that I have not changed the location of the cg of the
boat/trailer in relation to the fulcrum?

ADDITIONALLY, you've done NOTHING about the fact that the fulcrum is a
long ways from the CG in the Z direction.

Assume that the trailer is level. If the trailer is level, the Z
direction of the CG contributes absolutely nothing to the weight/balance
of the hitch vs. the wheels.

If you notice in the problem I gave you and Karen, I specified that the
trailer is level. So it doesn't matter where the cg is in the Z
direction.

Steve

"basskisser" wrote in message
om...


Yep, if you are not including the hitch in the calculations,

By "hitch" do you mean the draw bar portion that is rigidly mounted to the
tow vehicle, the actual ball joint, or the tongue assembly that is a rigid
part of the trailer?

Steves primary argument here is that you must consider the added weight of
the tongue extension. Please explain what your statement is inferring.

then yes.
What YOU seem to have not included, which would make YOUR analysis
fatally flawed, is the fact that the fulcrum point is NOT the CG,

Huh???

If the fulcrum point was at the center of gravity then the trailer would be
in perfect balance, I.E., no tongue weight.

and
ADDITIONALLY, you've done NOTHING about the fact that the fulcrum is a
long ways from the CG in the Z direction.

First off, if you are going to make this a multi-demensional problem, it
would be more accurate to refer to the "center of mass" instead of "center
of gravity".

All the discussions thus far have been a static problem."Static" is any
constant velocity situation. Note that Steve already defined a "given" as
the trailer was level, so for the purpose of discussion ignore going up or
down hills. As such, the Z axis is not a factor in the equations. The
center of mass will be somewhere above the center of gravity.

If you want to turn it into a dynamics problem then things get a bit more
complicated. Determining how the tongue weight will vary in an accelerated
frame of reference would require knowing where the center of mass is with
respect to the axel and hitch (ball joint). While you are at it, you might
as well consider the third dimension as well: if the "X" axis is for-aft,
the "Z" axis is up-down, then the "Y" axis is across the beam. If the
center of mass is not on the center line of the hitch then there will be a
moment about the hitch when the rig accelerates.

But that is irrelevant for the discussion at hand, which was limited to the
statics problem, which is pretty much a simple textbook exercise. If you
want to turn this into a full blown engineering project, give us the
necessary information and we can analyze it and tell you how the rig will
respond. But before you do that, why don't you demonstrate that you can do
the simple problem first?

Rod McInnis