Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Kinematics of Throwing Balls



"S.Goelzer" wrote:

I find this to be the most persistent problem in this topics.

I found this demo helps _some_ students.

Yup. Some. See below.

Tape a block of soft foam to the top of a dynamics cart (Pasco cart and
track). Block should be about the same volume as cart. Have student push the
cart using the foam. Student's finger should sink into foam when pushing.

Socratic method time:

How do you know when you are pushing?
(feel and SEE - maybe I should incorp a buzzer and switch too!)
When did the push end?
Did the push continue after you stopped touching the foam?
If the foam wad still being pushed after you stopped touching, what shape
would it have?
How is the motion of the cart different when you are pushing and when you
are not?

Push the cart to the student and have the student stop the cart by pushing
on the foam. More questions.

I really like that demo.

Some remarks:

1) Scott is wise to treat the horizontal acceleration
situation before the up/down throwing situation. Learning
proceeds step by step. If the students are confused
by the complicated situation, pick it apart into
sub-problems and deal with the misconceptions one
by one.


2) The Socratic method seems to me a double-or-nothing
proposition. For _some_ students, namely the ones who
have have the right level of background, they learn a
lot. But for other students who don't have sufficient
preparation, they're just lost and symied.

Definitely the method should be used, but only after
sufficient groundwork has been laid.

I suspect it'll take Tina a day or two to get students
to the point where Scott's demo would be effective.

Rick Tarara wrote:

... the standard Aristotelian viewpoint and you can bank on the fact
that more than one of your students will be thinking that way!

Yup.

3) It's easy for us professionals to forget that the
ideas involved here are nontrivial and counterintuitive.
Before Galileo's time, people thought that stasis and
friction were the natural default condition, so that
anything else (such as steady motion) required explanation.
It was a major breakthrough to change the point of view
to say that steady motion was the natural default
condition, so that anything else (such as decaying
motion due to friction) requires explanation.

Students weren't born knowing the right way to think
about this. The first time they see this material,
they have to make some major conceptual shifts.