Re: [Phys-L] Dirigible Flight Question - Would anyone like to try this....?

[Dan Beeker <debeeker@comcast.net>]

I sort of tried the ramp thing - once. I have an old 26 ft boat trailer 
I use to haul mowers between my house and my dad's house. It is very 
light and has a neat feature where you pull a bolt and the bed will tilt 
up. One then only needs a very short ramp to get things onto the 
trailer. It is evening and starting to get a little dark outside and I 
am in a little hurry as the lights don't work on the trailer - so you 
can probably guess the rest of the story. I hook up the trailer, pull it 
into the back yard, disconnect the bolt and hook up the ramps. As I 
start driving the mower onto the trailer everything is going fine, the 
bed tilts up just as it should and I proceed to drive onto the trailer. 
But as soon as I get most of the weight of the mower on the back of the 
trailer the whole front end of the trailer lifts up some 4 or 5 ft into 
the air. Yes, I forgot to tighten the hitch. Moving too quickly to do 
anything except say "Oh sh_ _ ! I watch in horror as I progress forward 
and the center of mass changes and the tongue of the trailer starts to 
come down, seemingly right on top of the tail gate of my rather new pick 
up. Amazingly, the coupler misses the taol gate and falls right onto the 
ball. I am saved from having to explain how I got the dent in the tail 
gate. If I had had time to hit the brakes on the mower, impulse and 
momentum would have undoubtedly resulted in a dent of some kind. I now 
check carefully and force myself not to get into a rush when I hook up 
the trailer. I also check my fly periodically.

Dan


On 11/6/12 12:00 PM, phys-l-request@phys-l.org wrote:
> Message: 3
> Date: Tue, 6 Nov 2012 09:55:25 -0600
> From: "John Clement"<clement@hal-pc.org>
> To:<Phys-L@Phys-L.org>
> Subject: Re: [Phys-L] Dirigible Flight Question
> Message-ID: <EC44D84D8DA547018904117E8E4337C4@ClementPC>
> Content-Type: text/plain;	charset="us-ascii"
>
> I think the historical definition of dirigible has been completely settled,
> but not necessarily the popular definition.  The language changes faster
> than the dictionaries.  One educated person I asked said a dirigible was a
> cigar shaped object that flew around.  The identification of dirigible with
> a rigid airship may come because "rigid" is in the word.  It is like
> students reaction to "penal institution" as if it were dirty.
>
> Real world problems are great for PhDs to argue over, and also for graduate
> students.  But when it comes to teaching students they need to be selected
> for suitability or reduced to simpler cases.  According to Shayer & Adey
> students ability to think improves if you pose puzzling problems, but not
> too puzzling.  Plain straight forward problems do not improve thinking.  So
> the full blimp problem is not suitable for most students and needs to be cut
> down a bit.  If you pose a problem which is far outside the zone of proximal
> development the student will just shut down in most cases.  Of course there
> is always the 1% who will work till exhausted, of which we are probably
> prime examples.
>
> I agree that textbooks have waaay too many plug and chug problems, and the
> instructors tend to assign them.  By contrast Minds on Physics is designed
> to force students to tackle problems where thinking first is important.
>
> Unfortunately when someone is asking a question about a cut down problem
> designed for students, most of the responses on this list are unsuitable for
> students, but very interesting to most of us.  So useful answers are
> actually only useful if they address the intended application, student
> education or real world engineering.  I do not know what prompted the
> blimp/dirigible/Zeppelin question, so the real world response might have
> been suitable.
>
> By the way, the 45 degree ramp can be perfectly 45 degrees if it pivots at
> the top to change from 45 up to 45 down like a teeter totter.  Of course
> this assumes the ramp is longer than the wheebase of the car.  Would anyone
> like to try this with their own car???
>
> John M. Clement
> Houston, TX

--
Dan Beeker