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Re: Free Body Diagram



I try to get them to focus on "What's the force
diagram; does the Earth ever stop its downward pull?"
If they've internalized that a net force means there
is acceleration, they don't have any difficulty. But,
that's a might big if. John Barrere Apex HS, Apex,
NC
--- Chuck Britton <britton@NCSSM.EDU> wrote:
> searching for
> the words that my high school class will
understand and will convince
them (and me) why one is correct and the other
incorrect.

The idea that the vertical acceleration goes to
zero is actually a variant
of the common misconception that students have.
They think that the
acceleration goes to zero when a ball is thrown up
and reaches it's peak
where the velocity is zero. Students may wish to
hang onto that explanation
as the misconception is fairly resistant to change.

VEEEEERY resistant to change!!!!!!

But, long before the idea of a free body diagram is
approached, the
students should have worked MANY velocity vs. time
graph type
problems.

Most HS students can reach the point of correctly
graphing the
vertical velocity of an object that is thrown
upwards into the air.

Once they have drawn this graph - they STILL will
need time to beat
their head against the idea that:
the slope is constant
and that
the slope is the acceleration
so

the acceleration is NOT zero as the graph
crosses the x-axis.

Just because we can recite the correct words, does
not guarantee that
we know what we are talking about.

Velocity graphs will sink in better than words for
some of the more
visual thinkers in your classes.

This posting is the position of the writer, not that
of SUNY-BSC, NAU or the AAPT.


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This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.