Saturday, 3 December 2016

Thursday, 1 December 2016


As far back as the late 1800s, U.S. physics teachers expressed many of the same ideas about physicseducation reform that are advocated today. However, several popular reform efforts eventually failed to have wide impact, despite strong and enthusiastic support within the physics education community. Broad-scale implementation of improved instructional models today may be just as elusive as it has been in the past, and for similar reasons. Although excellent instructional models exist and have been available for decades, effective and scalable plans for transforming practice on a national basis have yet to be developed and implemented. Present-day teachers, education researchers, and policy makers can find much to learn from past efforts, both in their successes and their failures. To this end, we present a brief outline of some key ideas in U.S. physics education during the past 130 years. We address three core questions that are prominent in the literature: (a) Why and how should physics be taught? (b) What physicsshould be taught? (c) To whom should physics be taught? Related issues include the role of the laboratory and attempts to make physics relevant to everyday life. We provide here only a brief summary of the issues and debates found in primary-source literature; an extensive collection of historical resources on physics education is available at

Why and how should physics be taught?

When courses in physics (then called “natural philosophy”) were introduced as part of the curriculum in the early academies and very first high schools in the early 1800s, the justification was explicitly practical: knowledge of physical phenomena was taught so people could put it to use in their everyday lives. By the early 1880s, however, high school physics teachers would express a multitude of reasons for teaching the subject, including that of training the mind “to habits of accurate observation and of precise and clear reasoning.” Hands-on laboratory activities came to be seen as necessary, so that physics students could learn “how to observe, compare, and draw conclusions of themselves,” or, in short, “to catch the spirit of inquiry.
Around this time the so-called “inductive method” was widely favored, referring to experimentation that led to student-generated models and explanations for observed phenomena: “[W]e first observe the phenomena sharply and then seek for a cause or for the law according to which the forces act….if the guess is a definite one, definite conclusions (deductions) can be drawn from it which will lead to new observations or experiments….we…continue until one explanation remains that is consistent with all our knowledge and stands all the tests we are able to apply.
Laboratory-based instruction spread rapidly among both high schools and colleges. The well-known “Harvard Descriptive List,” a laboratory guide written by E. H. Hall, incorporated many questions, specifically designed to lead physics students to develop models and explanations to account for their observations: “[I]t has been thought best…to put the student, so far as is practicable, into the attitude of an investigator seeking for things unforetold….He should not be told what he is expected to see, but he must usually be told in what direction to look. He should be required to draw inferences from his experiments.
A generation later, these themes were revisited by research physicists such as the University of Chicago’s R. A. Millikan, who had a special interest in improving both high school and college physics instruction. Millikan succinctly expressed the views of many physics educators regarding the value of physics, saying that:
“[T]he material with which it deals is almost wholly available to the student , so that in it he can be taught to observe, and to begin to interpret  the world in which he lives, instead of merely memorizing text-book facts, and someone else’s formulations of so-called laws….The main object of the course in physics is to teach the student to  to begin to construct for himself…an orderly world out of the chaotic jumble of phenomena which observation presents to him” [emphasis in original].
As these various quotes indicate, early instructional ideals were often envisioned as being based on the inductive method. However, around the turn of the century, an increased emphasis on college preparation along with a growing number of topics to be covered led high school physics to focus excessively on abstract principles and mathematical computations having little physical context, and to a decreasing emphasis on scientific investigation. Cookbook-style laboratory activities took the form of step-by-step procedures, encouraging rote practice and mindless manipulations of laboratory apparatus, rather than inductive reasoning. By 1906, many physics educators had concluded that instruction in physics had gone seriously astray, departing from its original objectives, and they argued strongly for a return to those objectives. For example, physicist C. R. Mann advocated laboratory-based investigations that would engage students’ intuitive thinking, promote inductive reasoning, and help students experience the “spirit of science,” which he defined as a belief that “the world is a harmonious and well-coordinated organism and that it is possible…to find harmony and coordination.” The “New Movement Among Physics Teachers” attempted to gather support for reforms aimed at goals such as this. Later, the increasingly popular “project method” saw students engaged in practical investigations of topics that might arise from their everyday lives and experiences. 
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Wednesday, 30 November 2016

Inside tiny tubes, water turns solid when it should be boiling

It’s a well-known fact that water, at sea level, starts to boil at a temperature of 212 degrees Fahrenheit, or 100 degrees Celsius. And scientists have long observed that when water is confined in very small spaces, its boiling and freezing points can change a bit, usually dropping by around 10 C or so.
But now, a team at MIT has found a completely unexpected set of changes: Inside the tiniest of spaces — in carbon nanotubes whose inner dimensions are not much bigger than a few water molecules — water can freeze solid even at high temperatures that would normally set it boiling.
The discovery illustrates how even very familiar materials can drastically change their behavior when trapped inside structures measured in nanometers, or billionths of a meter. And the finding might lead to new applications — such as, essentially, ice-filled wires — that take advantage of the unique electrical and thermal properties of ice while remaining stable at room temperature.
The results are being reported today in the journal Nature Nanotechnology, in a paper by Michael Strano, the Carbon P. Dubbs Professor in Chemical Engineering at MIT; postdoc Kumar Agrawal; and three others.
“If you confine a fluid to a nanocavity, you can actually distort its phase behavior,” Strano says, referring to how and when the substance changes between solid, liquid, and gas phases. Such effects were expected, but the enormous magnitude of the change, and its direction (raising rather than lowering the freezing point), were a complete surprise: In one of the team’s tests, the water solidified at a temperature of 105 C or more. (The exact temperature is hard to determine, but 105 C was considered the minimum value in this test; the actual temperature could have been as high as 151 C.)
“The effect is much greater than anyone had anticipated,” Strano says.
It turns out that the way water’s behavior changes inside the tiny carbon nanotubes — structures the shape of a soda straw, made entirely of carbon atoms but only a few nanometers in diameter — depends crucially on the exact diameter of the tubes. “These are really the smallest pipes you could think of,” Strano says. In the experiments, the nanotubes were left open at both ends, with reservoirs of water at each opening.
Even the difference between nanotubes 1.05 nanometers and 1.06 nanometers across made a difference of tens of degrees in the apparent freezing point, the researchers found. Such extreme differences were completely unexpected. “All bets are off when you get really small,” Strano says. “It’s really an unexplored space.”
In earlier efforts to understand how water and other fluids would behave when confined to such small spaces, “there were some simulations that showed really contradictory results,” he says. Part of the reason for that is many teams weren’t able to measure the exact sizes of their carbon nanotubes so precisely, not realizing that such small differences could produce such different outcomes.
In fact, it’s surprising that water even enters into these tiny tubes in the first place, Strano says: Carbon nanotubes are thought to be hydrophobic, or water-repelling, so water molecules should have a hard time getting inside. The fact that they do gain entry remains a bit of a mystery, he says.

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