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From the lab, students 'create' the model xf=vt+xo
The Modeling Physics approach does a LOT to resolve student graphing
challenges. A lot.
Learning the modeling method is well worth the time and effort. I
highly recommend giving it a shot.
Students can do the math because most of the math problems don't
require any thought about physics. They have a 3 or 4 variable equation
(maybe 2
eqns) and they plug n chug. It is often done with no physics thought.
Paul.
.:. Sent from a touchscreen .:.
Paul Lulai
-------- Original message --------
From: Anthony Lapinski <Anthony_Lapinski@pds.org<mailto:Anthony_Lapinski@pds.org>>
Date: 07/30/2013 9:59 AM (GMT-06:00)
To: Phys-L@Phys-L.org<mailto:Phys-L@Phys-L.org>
Subject: Re: [Phys-L] [SPAM] Re: The Make-Believe World of Real World
Physics
Allow me to jump in here about graphs. I think kids know how to graph
functions in their math classes. Then they come to physics, and it's a
whole new ball game. So difficult for them, especially with slopes.
Then, I give them a few constant slope lines on a "d-t graph" and ask
which has the highest acceleration. They just confuse the axes and
think it's a v-t graph (like something they've seen before). Some just
never understand graphs. Kids generally find math problems the easiest.
Concepts and graphs are more difficult.
Not sure what the solution is. Kids have difficulty thinking in school
these days, which is why they find physics challenging. It requires
them to think in ways they never have before. And thinking requires
effort. And they have other classes, XC activities, and social lives.
What to do???
Phys-L@Phys-L.org<mailto:Phys-L@Phys-L.org> writes:
I think there is real value in getting students to use graphs to
understand situations and solve problems. But first they have to
understand graphs, and I don't think enough time is spent in math or
physics on that. Do students understand what the points on the graph
represent, do they understand what horizontal and vertical intervals
represent? How do we know they do understand.
These graph solutions can be done with constant velocity problems
first and then advanced to more complicated situations as the student
understanding develops.
Average velocity also has extra meaning when you look at graphs and begin
to talk about slope. I suspect your concern has more to do with the
abstract nature of the way the problem is presented, rather than about
the content. What say you?
joe
On Jul 30, 2013, at 8:44 AM, Philip Keller wrote:
I agree. These are nice math puzzles but they barely feel like
physics
to
me. They have the "if Mary can mow a lawn in 40 minutes..." feel to
them.
I see this particular type of item as part of the black hole of
kinematics. I would much rather skip this and spend that time
trying
to
get my students to use graphs to solve problems rather than formulas.
On Mon, Jul 29, 2013 at 9:40 PM, Paul Lulai
<plulai@stanthony.k12.mn.us<mailto:plulai@stanthony.k12.mn.us>>wrote:
I think this question (how fast / far to have a certain avg speed)
is
a
lot of work that isnt worth the payoff and is also a bit of a trap.
It feels like we are baiting them into trying to do it incorrectly.
I am sure there are science & technical folks that do a lot with
average
speed, but we do next to nothing with it in high school, except ask
trick
questions like this one. I suppose it is a way to check the
difference
btn
speed and the vector nature of velocity. It just seems like there
would be
other ways that could check the same conceptual point and be less
misleading.
I don't do much at all w avg speed. While I am sure it can be
helpful
in
some situations, this isnt an area I am going to go crazy preparing
for.
Paul
.:. Sent from a touchscreen .:.
Paul Lulai
-------- Original message --------
From: Anthony Lapinski <Anthony_Lapinski@pds.org<mailto:Anthony_Lapinski@pds.org>>
Date: 07/29/2013 6:51 PM (GMT-06:00)
To: Phys-L@Phys-L.org<mailto:Phys-L@Phys-L.org>
Subject: Re: [Phys-L] [SPAM] Re: The Make-Believe World of Real
World Physics
Makes sense.
Acceleration is hard for kids. I begin the course with speed,
average speed, velocity, etc. Another "basic" problem/idea kids in
my class
get
wrong is about average speed:
Must average 200 mph over 2 laps. After one lap, you've only
averaged
150
mph. What must be your average speed for the second lap?
Many want to say 250 mph as they want to just average the speeds.
They forget the definition that avg speed = distance/time. Even
after doing problems in class and for homework, they continue to
miss this
question
(and variations of it) on the test. Physics requires a different
way
of
thinking about the world.
You can simplify this with a related question:
On a trip to New York. One way is 60 miles. 60 mph going there and
30
mph
coming back. Is the avg speed for the entire trip less than equal
to,
or
more than 45 mph?
It's a great peer instruction question as the math is relatively
easy
to
do in your head, and those that understand the problem can explain
it
to
others. Still challenging for some. Very interesting discussions to
hear
in the classroom!
So do others teachers have similar experiences with these types of
average
speed problems?
Phys-L@Phys-L.org<mailto:Phys-L@Phys-L.org> writes:
I can certainly envision lots of students claiming the
acceleration
at
the peak is zero. However, i think this answer comes from
students trying to memorize physics points rather than think about
and analyze physics. In my experience, students that answer a=0
remember there is something unique about the top. They remember
something is zero and
they
go with a =0 since we are asking them about a.
If we ask them if there velocity at the peak will remain constant,
few
will say /yes the velocity will be 0 and will stay 0 at the top
forever
and the ball will never fall/.
Our challenge is to get them to analyze the scenario and avoid the
temptation to answer reflexively.
In my opinion, that is the challenge w a lot of the challenging
and trick/tricky physics questions students encounter in their
first
course.
Have a good one.
Paul.
.:. Sent from a touchscreen .:.
Paul Lulai
-------- Original message --------
From: Kirk Bailey <kirkbaile@gmail.com<mailto:kirkbaile@gmail.com>>
Date: 07/29/2013 5:01 PM (GMT-06:00)
To: Phys-L@phys-l.org<mailto:Phys-L@phys-l.org>
Subject: Re: [Phys-L] The Make-Believe World of Real World Physics
I can't remember where or when, but I know I read that the number
one misconception (based on how many students still missed it at
the end
of
the
course) was the acceleration of an object thrown straight up at
the
peak
of
its trajectory. Just understanding that it isn't zero at the top
is
a
non-trivial objective, and I don't see it as an easy question in
any student universe.
On Mon, Jul 29, 2013 at 4:19 PM, Anthony Lapinski
<Anthony_Lapinski@pds.org<mailto:Anthony_Lapinski@pds.org>>wrote:
Right. And a student in a physics class should answer it
differently (correctly). Acceleration = rate of change of
velocity = gravity = constant (in free fall).
Unless, of course, I am missing something or in a different
universe.
Phys-L@Phys-L.org<mailto:Phys-L@Phys-L.org> writes:
Folks on the street indeed are likely to think of acceleration =
speeding
up and deceleration = slowing down. therefore acc at top = zero.
Every beginning physics student should be able to think of the
velocity
graph with it's slope and areas included.
On Jul 29, 2013, at 3:36 PM, John Denker <jsd@av8n.com<mailto:jsd@av8n.com>> wrote:
You might be a redneck physicist if you buy 48 cans of Big
Flats beer and cool them off using liquid nitrogen.
On 07/29/2013 07:29 AM, William Maddox wrote:
In this universe the acceleration of a ball at peak question
would
not be considered ill posed in the context of a physics test
following chapters on projectile motion and gravity.
Congratulations on living in such a nice universe (A).
Meanwhile, there are plenty of people on this list who live in
a different universe (B), where students find this question
hard or at least counterintuitive.
I reckon this list is extremely valuable, because it allows us
to recognize and discuss the difference between these two
universes.
-- Why is this an easy question in one universe but not the other?
-- Can we move everybody from universe (B) to universe (A)?
-- If so, how?
I remind everybody yet again that many things that seem hard at
the beginning of the road seem easy (and are easy) at the end
of the road.
=============================
Physicists tend to write as little as they feel necessary.
... which can be a big part of the problem, if they misjudge
what is "necessary". This is known to be a problem whenever
experts are talking to non-experts, including students.
Miscommunication makes things hard, even things that ideally
"should" not be hard.
_______________________________________________
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http://www.phys-l.org/mailman/listinfo/phys-l
_______________________________________________
Forum for Physics Educators
Phys-l@phys-l.org<mailto:Phys-l@phys-l.org>
http://www.phys-l.org/mailman/listinfo/phys-l
_______________________________________________
Forum for Physics Educators
Phys-l@phys-l.org<mailto:Phys-l@phys-l.org>
http://www.phys-l.org/mailman/listinfo/phys-l
--
Kirk Bailey
Never use a big word if a diminutive synonym is as efficacious.
_______________________________________________
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http://www.phys-l.org/mailman/listinfo/phys-l
_______________________________________________
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_______________________________________________
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http://www.phys-l.org/mailman/listinfo/phys-l
_______________________________________________
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http://www.phys-l.org/mailman/listinfo/phys-l
Joseph J. Bellina, Jr. Ph.D.
Emeritus Professor of Physics
Co-Director
Northern Indiana Science, Mathematics, and Engineering Collaborative
574-276-8294
inquirybellina@comcast.net<mailto:inquirybellina@comcast.net>
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