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Re: improving textbooks -- some modest proposals



As a case in point I am now looking at Prentice Hall "Exploring Physical
Science, Texas Edition" which is a "new" edition about 5 years ago. It is
copyrighted 95 and 97. Editorial staff: Lorraine Smith-Phelan & others,
Natonal Science Consultants: C. Balko, P. Cominsky, J. Dennard, K. French,
B. Underwood. I don't recognize any of the names, does anyone else know any
of these people? It has a list of 5 contributing writers and about 35
content reviewers and 9 teacher advisory panelists. Again there are no
names that I recognize and only 1 is a PhD.

Now forces and NTN's laws are covered in 1 chapter pp 323-347.

NTN's 3rd law is introduced in boldface as "The third law of motin states
that for every action, there is an equal and oposite reaction". It then
goes on to state in the next sentence, as an afterthought that the forces
are equal and opposite and that forces come in pairs. This immediately sets
up a misconception.

On the same page it shows a jumper jumping out of a canoe in 1 frame and
landing in the water in the next frame. She misses the dock because the
canoe moved backward. There are equal and opposite arrow showing her motion
and the canoe's motion, implying that they are equal. A question asks which
of NTN's laws explains why the juper lands in teh water, not on the dock.
Again NTN3 is equated with motion.

On the next page next to a picture it asks how does NTN3 explain th movment
of a water sprinkler. It has arrows showing the motion of the water and
motion of the sprinkler. Again it reinfoces a wrong interpretation of NTN3.

On another page it shows a strobe picture of 2 balls falling and the balls
are different sizes. You can clearly see the effect of the acceleration on
the balls. Then underneath the picture it says "Two objects will fall to
the Eath at exactly the same rate, regardless of their masses." Now if they
had used the word acceleration it might be correct. However the word rate
is usually used to mean speed or velocity and the implication might be taken
that the speed is uniform. There is no information to guide the reader
about the meaning of the picture. Strobe diagrams are not instantly
understood by students. They need to be taught and studied.

On another page they use arrow width to represent force size and have the
lengths the same so that they meet. This means that large forces have wide
short arrows and small forces long narrow arrows. This will later cause
difficulty when studying vectors.

When they introduce Weight = m g they use g as 9.8 m/s^2. Then they proceed
to do the calculation and magically end up with the answers in Newtons. No
explanation of units is done. Under this circumstance they should at least
use g = 9.8 N/kg. The latter is preferred by the UMPERG group and by the
physics text reviewers in TPT as it is more correct and MUCH less confusing.
I realize the more correct is in dispute on this list, but the TPT article
edited by Cliff Swartz did say it.

I find the writing to be reasonably interesting, and it even takes a
historical perspective in an attempt to bring the ideas into focus. However
there is no attempt at exploration before the reading. All of the labs are
verification labs at the end of the chapter.

The extremely short chapter review has very simple questions which can be
mainly answered by rote memorization. One question "The force that opposes
the motin of an object is called" has a multiple choice answer "friction".
The article should be "A" rather than "The".

One question at the end asks "Although Newton's first law of motino has two
parts, they actually say the same thing. Explain how this can be true using
what you learned about grames of reference" To answer this the student has
to go to a previous chapter to find frames of reference. This is actually
an extremely advanced question, and they are given little support for it.
Students actually have a certain inherent understanding of frames of
reference. What they don't understand is how to judge something from the
correct frame of reference. When asked about a box inside a car moving past
you at 60 mph they will invariably say it is rest even though they are told
that they must judge it from your point of view. Similarly they will say a
coat on top of a car accelerating to the right will fall to your left when
you are standing next to the car.

I find that the chapter provides little support for dispelling
misconceptions. Often they use the word move when they should use
accelerate. The text makes some attempts, but is not adequate, and does not
provide the physical activities which are necessary to help students
understand the concepts. I see places where they are setting up the
misconception that a force is necessary to keep a ball going. This section
would be covered in a week or less so students would probably show no change
on a good conceptual test such as the FCI. This is what I can come up with
in only 30 min of work.

The book is actually very attractive, and the pages are not too busy. Just
glancing at it I would like it. However...

John M. Clement
Houston, TX