Re: Gain and Mechanical advantage confusions

[Rick Tarara <rtarara@SAINTMARYS.EDU>]

I would avoid general definitions in this area--rather discuss the _concept_
of gain or mechanical advantage.  Then look at individual machines and talk
about what they do.  Then you can define gain/mechanical advantage more
meaningfully.   For example, I do an inclined plane experiment where we
define the mechanical advantage as the (weight lifted)/(force applied)  and
the efficiency as (the useful work done)/(energy input).  Both definitions
are somewhat specific to this machine and our use of it.  Don't be too
concerned that the determination of mechanical advantage changes from
machine to machine--that's the nature of the beast.

Rick

**********************************************
Richard W. Tarara
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556
rtarara@saintmarys.edu

FREE PHYSICS INSTRUCTIONAL SOFTWARE
www.saintmarys.edu/~rtarara/
PC and MAC software
NEW! SIMLAB2001--DYNAMIC CARTS now available.
CD-ROMs now available
******************************************************


----- Original Message -----
From: "Gary Turner" <turner@MORNINGSIDE.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Tuesday, November 20, 2001 11:16 AM
Subject: Gain and Mechanical advantage confusions


> 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?