Yup, exactly. You don't have to believe experienced mechanics, or even old
physics majors like me. Just pick up a book, any book that has a chapter
on classic physics covering levers and force. Basic high school stuff.
Now I'll compound the problem. The pressure in the system doesn't matter
much as long as the fluid is not compressible. You never need to know what
it is to solve for force, as Mark's equation below implies. Force applied
and relative area are the only variables required to solve for output
force. Input travel and relative area are the only variables required to
solve for output travel.
Like the guy says "youse could look it up".
-----Original Message-----
From: Mark J. Bradakis [mailto:mjb@cs.utah.edu]
Sent: Wednesday, June 20, 2001 2:01 PM
To: fot@autox.team.net
Subject: Re: GT-6/Spitfire brakes
If you take the same setup and apply the 10 psi to a 0.5 square inch
piston you are now getting 10 lbs per 1/2 square inch which is 20 psi
and
you get 20 lbs. of force out of the system.
No, you don't. This is nonsense. If you have a pressure of 10 psi
(that's
pounds per square inch), you have a pressure of 10 pounds per square inch,
over every single bit of area in the entire system. The insides of the
brake
or clutch line, the bore of the fittings, against the base of the bleed
screw,
*any* area inside the system will have that same force.
If that pressure is applied to 1 square inch, you get 10 pounds of force.
If that pressure is applied to 2 square inches, you get 20 pounds of
force.
If that pressure is applied to 1/2 square inch, you get 5 pounds of force.
The force in pounds is the product of the area times the pressure, simple,
basic high school math. Write out the equation, and see how the units
cancel:
pounds pounds inch * inch
Force ------- = Pressure ----------- x Area ------------
1 inch * inch 1
This is classic Newtonian physics. The work that goes in is the same as
the work that comes out. That is, negating the effects of mechanical
friction
and things like the force used to distort the clevis, the pins, etc. on
every
pedal application. Here I use work in the classic physics definition, a
force
applied over a distance.
People are confusing volume, pressure, area and distance in the situation.
They are all related by basic mathematical equations.
mjb.
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