You often need to review your approach to any given
problem, until you get to its very core. To this purpose, Michel Joly
(1993) suggests two techniques: Crossed Segmentation and
Causal Analysis .
Causal Analysis belongs to external mapping (see the
author’s example in “Idee che rendono…come trovarle”)
though it might be used in internal mapping, as well.
An oil production and distribution company was
looking for something to propose to car drivers. So, the company members
examined car drivers’ problems and tried to work out a product
to solve them. Winter was approaching and soon snow lovers would leave
for a week’s skiing holiday. The company managers thought about
car drivers who are not used to cold. They would leave the city and
finally get to the mountain resort at dusk, with their folks. A few
miles before arriving, they would slip on an ice block, smash against
a rail and begin their snow holiday in a freezing luxurious hotel,
having to pay for an unexpected accident.
The real problem was how to prevent a car from skidding
on the ice.
Why does it skid? Because the rubber friction coefficient on the ice
is low. Why is it low? Many would answer that ice is smooth. Is it
true that a smooth surface has a low friction coefficient?
You realize that it is not true if you place a sheet
of paper on an upright glass and remove the air between the two: your
sheet does not drop or comes off only after a while.
Therefore there must be another reason. Why then two surfaces supposed
to have a high friction coefficient could spoil our poor driver’s
holiday?
A group of technicians was confronted with this issue; some of them
stated that there was something between the rubber and the ice, maybe
some water. Why water? Where might it come from?
What about hot rubber? Indeed, it is hot but it comes into contact with
the ice only for a short while, therefore it cannot melt the ice crust.
What about rubber friction? Cars skid even when they are standing…
How about the tyre pressure on the ice? It is true; ice melts under
a certain pressure, even at 5 or 6 degrees below zero.
Which is the tyre pressure on the ground? It is about 2 bars (pumping
pressure). Is it enough to melt the ice straight away (adiabatic melting,
id. without heat transfer)? Experts say no.
What then? The water hypothesis was not odd at all. Do such pressures
really exist? After all, pressure results from a mass applied to a surface.
What about the contact surface between the tyre and the ground? A careful
test proved that the tyre gets worn on the road and has more or less
evident harms (shellings, scratches, furrows). The contact does not
take place on a huge surface; on the contrary it is scattered within
an apparent contact surface with the ground or the ice. So, the car
weight rests on a few contact points, thus putting a pressure that is
much bigger than 2 bars, id. over the adiabatic limit. The ice placed
on the contact points melts under the wheels pressure. The car begins
to skid, the pressure pushes a bit further, ice melts and the car cannot
stop.
So, if it works like this, how can you remove irregularities and make
the surface smooth?
Obviously, you do not need to always adjust tyres, otherwise they would
get spoiled in a short time.
What about filling holes? With what then?
By dint of thinking, they generated the following idea: they covered
rubber with a kind of foam, so they created an undamaged contact surface
for the ice crust. In this way, they reduced peak pressure and without
peak temperature ice did not melt any longer.
This product can now be found in aerosol cans; drivers that leave for
skiing resorts can buy it before smashing against a rail on a freezing
road. However, the foam layer fades away and needs to be rebuilt…
Brilliant, isn’t it? Our grandmothers wore their woollen tights
on their shoes, thus filling any holes and increasing the real contact
surface between their feet and the ice crust. As a result, they did
not risk breaking their legs so much.” (Joly, 1993)