Re: Gain and Mechanical advantage confusions

[Tom Ford <tomford@THESCIENCESOURCE.COM>]

Personally, I am confused by any reference to "gain" in this context. I
have found it useful to rely on the terms "mechanical advantage" and
"mechanical disadvantage". In a simple machine, e.g., a force advantage is
accompanied by a displacement disadvantage -- and the other way around.
Real machines might exploit either of these. The ideal mechanical advantage
comes from observing the geometry of the simple machine, while the actual
mechanical advantage comes from measuring the forces involved. All
advantage is given in ratio format, so it is possible to ask for a pulley
system with an Ideal Mechanical Advantage of 1.5 : 1 (without using half a
pulley, of course).

Tom Ford

At 10:16 AM 11/20/01 -0600, you wrote:
> I wanted to throw this out to the community, see what the general opinion
> is on gain and/or mechanical advantage for simple machines.  Here are some
> definitions I have come across-
>
> Force gain (=F/f)
> Distance (or displacement) gain (=D/d)
> Ideal gain (=D/d)
> Actual (or real) gain (=F/f)
> Mechanical advantage (usually = F/f, but also written as D/d)
>
>
> Which of these are most useful to students?  Are some terms used
> preferentially over others?
>
> Personally, I have a problem with the force - distance gain pair because
> one gains at the expense of the other.  I think this is confusing to talk
> about a 'gain' in force and a 'gain' in distance at the same time.
>
> The ideal - actual gain pair is also confusing because the "ideal"
> situation is not the ratio of distances.  If you account for stretching and
> flexing, the "distance gain" is certainly not ideal.  In some cases (such
> as a flexing lever), it seems that the imperfections related to distance
> are more significant than the imperfections related to force.  However,
> when you have a pulley with mass and friction, the imperfections related to
> force will dominate.
>
> Mechanical advantage is just outright confusing when it is sometimes used
> for distance and sometimes for force.  If we restrict it to one, what
> should we call the other one?  You have to assume the force and distance
> ratios are different to get efficiency.
>
> Are there other, more logical, terms out there?