Re: Relationship between Earth Moon

[John Clement <clement@HAL-PC.ORG>]

I think that Tina's work probably does show that there is a major
misconception about the size and distance of the moon.  However, there is
some truth in the questions about whether the students really understand
scale diagrams.  Since 25% of my advanced students, and 75% of my regualar
students (16/75 students are advanced) do not understand ratios, they
probably also do not understand scaling. Astronomy is often a course which
students are likely to take with the mistaken idea that it is easier than
physics, chem., or bio., so a large fraction of students in the intro. class
are likely to have lower thinking skills, and are not likely to understand
ratios.

The idea that the mass of the moon is 1/6 of the earth's, is a natural
conclusion based on the 1/6 value for g on the moon.  Since the value of g
depends on 2 variables, understanding the actual reason for g will be
impossible for the majority of students.  This require understanding
equations with 3 variables, which is a very high level skill generally
accessible only to formal thinkers.  For a fuller explanation of this see
Shayer&Adey "Really Raising Standards".  Notice that this same difficulty
applies to any 3 variable equation such as F=ma, Density=mass/volume ...

F=mg can be easier if g is always given as 9.8N/kg, and is not treated
initally as a variable.  I would also agree with previous posts that treat g
as a field strength, but I would never use that term.  Instead I think that
initally students need to come to understand g as an experimental result
which allows one to calculate the force once one knows the mass.  Later on
the idea can be introduced that it is not universal, and that it varies from
one planet to another, and even later that it can be calculated from NTN's
gravitation law.  I would always call the acceleration due to gravity a_g
(_ means subscript), and perhaps more advanced students could learn the
connection between the 2 ideas.  The equivalence of units is very difficult
for lower students, as most of them can not handle fractions properly.  They
will divide m/s by s and then say that the seconds cancel to give m. Of
course they will sometimes say that dividing 1/2 by 2 will give 1, but if
you present them with the idea of dividing a half pie into 2 pieces, they
will not see the contradiction.  To them math is just a set or memorized
tricks, with little connection to reality, and they do not understand that a
contradiction is showing them that their original result is wrong.

John M. Clement
Houston, TX


> Fine.  Is there somewhere in the hundred pages where a student claims
> that he/she can fly to the moon?
>
>
> On Fri, 14 Sep 2001, Tina Fanetti wrote:
>
> > Uhm.. It is justified in my 100 page Masters thesis
> >
> > Tina Fanetti
> > Physics Instructor
> > Western Iowa Technical Community College
> > 4647 Stone Ave
> > Sioux City IA 51102
> > 712-274-8733 ext 1429
> >
> > > > > Jack Uretsky <jlu@HEP.ANL.GOV> 09/14/01 09:47AM >>>
> > Hi Tina-
> >         Sorry, but I don't think that you have justified your conclus=
> > ion
> > that "most think ..."  More likely, I think, is the conclusion that y=
> > our
> > people do not understand the notion of a scale drawing in the context=
> >  of
> > the given astronomy problem.
> >                                 Regards,
> >                                         Jack
> >
> >
> >
> > On Fri, 14 Sep 2001, Tina Fanetti wrote:
> >
> > > > > > I find it hard to believe the statement above.
> > > How did you obtain the data that suggests that
> > > "most students in college do not grasp the relationship
> > > between the earth and the moon" and that "most think
> > > that the moon is close enough to take a plane to?<<<<
> > >
> > >
> > > I came to this conclusion based on interviews and on surveys handed=
> >  o=3D
> > > ut to students.  The survey questions were:
> > >
> > > 1..  Explain, as clearly as you can, why it is the Moon sometimes a=
> > pp=3D
> > > ears as a full bright circle like this,  (drawing of circle)=3D09an=
> > d so=3D
> > > metimes the Moon can appear as a crescent like this, (drawing of cr=
> > es=3D
> > > cent).
> > >
> > > 2.  .  On the back of this page, draw the Earth-Moon System as a sc=
> > al=3D
> > > e model.  (This means draw the Earth and Moon the correct sizes for=
> >  a=3D
> > >  sheet of paper.  Also, make sure that you have the correct distanc=
> > e =3D
> > > apart for a sheet of paper.)  Don't worry about being exact, just b=
> > e =3D
> > > as close as you can.  Please explain why you drew the Earth-Moon Sy=
> > st=3D
> > > em the way you did.  Please be sure to label all the items in you s=
> > ke=3D
> > > tch!
> > >
> > > After collecting all the surveys, before and after instruction.  I =
> > me=3D
> > > asured the circles and set up ratios.  Most Student drew the earth =
> > an=3D
> > > d moon less then 3 earth diameters apart. =3D20
> > >
> > > I can send you the actual data if you would like
> > >
> > > Tina
> > >
> > >
> > >
> > >
> > > Tina Fanetti
> > > Physics Instructor
> > > Western Iowa Technical Community College
> > > 4647 Stone Ave
> > > Sioux City IA 51102
> > > 712-274-8733 ext 1429
> > >
> > > > > > Herbert H Gottlieb <herbgottlieb@JUNO.COM> 09/10/01 05:46PM >>>
> > > On Mon, 10 Sep 2001 10:09:53 -0500 Tina Fanetti
> > > <FanettT@QUEST.WITCC.CC.IA.US> writes:
> > > > I would have to agree with the statement that most students in
> > > > college do not grasp the relationship between the Earth and the M=
> > oo=3D
> > > n.
> > > =3D3D20
> > > > My thesis was looking at college students' scale of the Earth-Moo=
> > n
> > > > system and most think that the Moon is close enough to take a pla=
> > ne
> > > > to.
> > > >
> > > > Tina
> > >
> > >
> > >
> > >
> > > Herb
> >
> > --