Re: [Phys-L] backwards units

[Bill Nettles <bnettles@uu.edu>]

I was playing off of John Denker's tongue-in-cheek statement:
> -> 68.3 percent of all statistics are made up on the spot.
> -> Except on CNN, where it's 88.5 percent of the statistics.

BUT...in my  years of teaching, most of the wrong answers stem from poor control of negative signs (including while managing vector quantities, neglecting to specify positive directions, along with poor algebra, trig, and calculus manipulations, which require close attention to detail),  and incorrect unit manipulation.

When I find someone who is a beginning teacher of algebra in HS/MS/JHS I tell them "It's a minus sign." I then explain they should teach their students to examine their own work for sign errors when they can't get a problem correct.  After a semester, the teacher will tell me I gave them good advice.

When I have students work problems in physics class and they get the problem incorrect (the ones who actually get a final answer), the error is most often due to an algebraic or assigned direction minus sign error or they forgot to convert units.  I force them to find their mistake.  Those who never get an answer are usually the ones who never ask a question, and that frustrates me greatly because it's obvious that they are the ones who don't understand problem solving.  Reminds me of something like leading a horse to water ....

So, the source is my own experience.


-> -----Original Message-----
-> From: Phys-l [mailto:phys-l-bounces@www.phys-l.org] On Behalf Of
-> Richard Heckathorn
-> Sent: Thursday, May 07, 2015 7:41 PM
-> To: Phys-L@Phys-L.org
-> Subject: Re: [Phys-L] backwards units
-> 
-> Greetings, 95% of errors due to sign mistakes, and 4% due to unit
-> conversion problems if true is really telling us teachers what to focus on in
-> problem-solving.
-> 
-> What is the source of this information? My experience would say that
-> students have no clue how to even identify variables and unknown so they
-> can begin to solve a problem. Just an opinion.
-> 
-> Have a Great Day
-> 
-> Website rheckathorn.weebly.com
-> 
-> 
-> 
-> > On May 7, 2015, at 3:34 PM, Bill Nettles <bnettles@uu.edu> wrote:
-> >
-> > Statistics:
-> > 95% of physics problem errors are cause by sign mistakes. 4% are bad unit
-> conversions. The remainder are due to difficult physics.
-> >
-> > -> -----Original Message-----
-> > -> From: Phys-l [mailto:phys-l-bounces@www.phys-l.org] On Behalf Of
-> > -> John Denker
-> > -> Sent: Monday, May 04, 2015 8:21 PM
-> > -> To: Phys-L@Phys-L.org
-> > -> Subject: Re: [Phys-L] backwards units
-> > ->
-> > -> On 2015, May 04, , at 11:52, John Denker <jsd@av8n.com> wrote:
-> > ->
-> > -> >> I like to point out that getting the units wrong might cost you
-> > -> >> 328 million dollars
-> > -> >>    http://mars.jpl.nasa.gov/msp98/gif/m98patch.gif
-> > ->
-> > -> On 05/04/2015 05:08 PM, Bernard Cleyet wrote:
-> > ->
-> > -> > You mean  $125 M?
-> > -> >
-> > -> > This one?
-> > ->
-> > -> I mean this one:
-> > ->
-> > ->   http://mars.jpl.nasa.gov/msp98/orbiter/fact.html
-> > ->
-> > -> 327.6 million dollars.  Rounded off to 328.
-> > ->
-> > -> > http://www.cnn.com/TECH/space/9909/30/mars.metric.02/
-> > -> >
-> > -> > bc not certain he should believe CNN.
-> > ->
-> > -> When not sure, there are lots of ways of checking.
-> > ->
-> > -> 68.3 percent of all statistics are made up on the spot.
-> > -> Except on CNN, where it's 88.5 percent of the statistics.
-> > ->
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