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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.
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