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Re: [Phys-L] The Make-Believe World of Real-World Physics

My students find forces (Newton's laws, friction, centripetal force)
especially counterintuitive. Yes, the laws are simple to state, and
teachers understand them. But for students, they go against their personal
experience and that's what makes them counterintuitive and difficult to
grasp.There are other good examples of these, especially in circuits and
optics. I survey my students (anonymously) each trimester, and they share
what topics/concepts they find challenging

Phys-L@Phys-L.org writes:
Your original statement was that many physics CONCEPTS are
counterintuitive. These examples are not concepts, they are behaviors. I
agree the behaviors are counterintuitive, just like magic tricks. The
concepts which explain the behaviors are NOT counterintuitive. And just
like magic tricks, once you understand the concept, you're left to
appreciate the skill of the prestidigitator even if you understand the
concept.

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of Anthony
Lapinski
Sent: Tuesday, July 16, 2013 4:54 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] The Make-Believe World of Real-World Physics

These are just my observations over nearly 25 years of teaching -- at
four
schools in three states. Physics ideas make you really think, unlike
those in
biology or chemistry. I'm not really talking about falling bodies. You
can easily
drop two (different mass) steel balls, and they will hit at the same
time. This
might be counterintuitive, but at least students can SEE this demo. I'm
talking
more counterintuitive things like these:

MOTION: Throw a ball straight upward. What is its acceleration at the
peak?
The ball and three hill problem (constant angle, concave, and convex) -
which
hits the bottom first?

FORCES: Helium balloon in car. When the car accelerates, which way does
the
balloon move?
Two equal masses attached to the ends of a string which passes over a
pulley. What is the string tension?
Tug-of-war -- which team pulls with more force? What determines the
winner?

GRAVITATION: Orbiting astronauts in the ISS. They float, but is gravity
acting
on them?
SPRINGS: Cut a spring in half, what happens to its stiffness?
MOMENTUM: To best knock something over, would you throw a ball that
sticks or one that rebounds?
FLUIDS: When an ice cube melts in a glass of water, what happens to the
water level?
Stick your finger in a beaker of water on the scale (but don't touch the
bottom). What happens to the scale reading?

HEAT: Why do some pots have copper bases and steel sides?
Ball and ring demo. Heat it -- what happens to the hole?

ELECTRICITY: Three bulbs connected in series to a battery. Which bulb
receives current first?
SOUND: What wave property is primarily responsibility for your voice
sounding louder through a (non-electric) cheerleader horn?
OPTICS: To see more of yourself in a plane mirror, should you hold the
mirror
closer, farther, or do you need a larger mirror?
If you cover the top half of a lens, what happens to the real images
formed?

These are some of the many peer instruction questions I ask my (high
school) students for the topics I teach. Very practical and
counterintuitive as
they stump most of my kids, even my "honors" ones.
Would your students find these counterintuitive? These questions are
intended to make students think in ways they never have before. And
thinking (and, thus, physics) is difficult.

Anyone have other "counterintuitive" questions?


Phys-L@Phys-L.org writes:
-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of Anthony
Lapinski
Sent: Friday, July 12, 2013 10:19 AM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] The Make-Believe World of Real-World Physics

Compared to most other subjects they take in high school. This is
because
many physics concepts are counterintuitive. And then there's the math
element, reading/interpreting word problems, graphing, etc. Physics
IS difficult. I'm not comparing physics to "living in the real world"
--
that's apples
and oranges. I'm talking about physics as a part or their academics.
Toughest
(intro) subject they will take. This has been my experience.

You say many physics concepts are counterintuitive. As I get older and
teach more, I am doubting that more and more. I believe that what
seems to students to be "counterintuitive" is probably just a failure
to actually think about what is happening. Part of improving our
teaching is related to pointing the students to actually think about a
situation rather than merely reacting.

One of those counterintuitive concepts may be "falling objects near the
surface of the Earth accelerate at the same rate, ignoring air
resistance." (Don't pounce on my wording.) What we have to do is guide
the students to not think of acceleration as a "fundamental" property,
but to get them to examine the force. More massive objects DO have
more force on them , mg, where g is NOT the acceleration "of gravity"
but the strength of Earth's gravitational field. Another concept is
that the strength of the field doesn't depend on the falling object,
but on
Earth's mass and distance, etc. Then get them to think what the
associated acceleration should be (a = F/m = mg/m = g (for a numerical
answer, NOT a concept)).

As physicists teaching physics, we need to rid ourselves of the idea
that physics concepts are counterintuitive and begin to develop better
explanations that emphasize the intuitive basis of physics. And that's
why we should oppose biologists and mathematicians who took one
introductory physics course or passed some education multiple choice
test from EVER teaching high school physics. I'd rather receive a
student who never had physics in high school vs. one who had a poor
teacher.
_______________________________________________
Forum for Physics Educators
Phys-l@phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l


_______________________________________________
Forum for Physics Educators
Phys-l@phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l
_______________________________________________
Forum for Physics Educators
Phys-l@phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l