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发布时间:2013-12-13 12:02:14  

Introductory Physics for stthe 21Century

Why a New Introductory Physics Curriculum?

Case 1:Integrating aspects of contemporary physics

i ) emphatically demonstrates the power of physics principles and

develops knowledge that can ease students’ transition to more

advanced study.

ii) explicitly portrays physics as the vibrantly alive science that it is.

We can modify traditional treatments of the principles of dynamics using momentum and energy concepts so that it can be combined with a few contemporary ideas, e.g., a system’s internal energy contributes to its rest mass and is quantized, to make principled presentations of many 20thcentury discoveries.

Nuclear Atom Nuclear Fission and Fusion

Particle Decay and Reaction Energetics

Spectral-Line Emission and Absorption

Dark Matter Supermassive Black Holes

Aspects of Low-Temperature Thermal Physics

?

A Tongue-in-Cheek Overview of the 20thCentury Evolution of Physics Textbooks1910, Ganot1960 Halliday &

Resnick (from 1977)Steve Durbin, Purdue University2004 H&R/Cummings18th edition!

1949

1928, 1938

Millikan et al.Sears & Zemansky2004 S&Z/Young

190019201940196019802000

Why a New Introductory Physics Curriculum?

Case 2:The knowledge and skills that too many students take away from traditional physics courses is superficial, at best.

i ) evidence from research studies

ii) our own assessments based on subsequent student performance

A skater of mass m=50 kg,

initially at rest, pushes

away from the side of a

skating rink by exerting a

force perpendicular to

the boards of constant

magnitude F=200 N.

The force stops when she

has moved 0.25 m and her

hands lose contact with the

boards.

What is her final velocity? 1200?0.25??50?V22V2?2?V?1.414 m/s to the right

We can certainly argue that a performance like this is evidence of some understanding, but …

1200?0.25??50?V2

2

V2?2

?V?1.414 m/s to the right

Q1. Does any force do significant work on the skater in this situation?

A. Yes, the force she exerts on the boards

B. Yes, the force the boards exert on her

C. Yes, the net force exerted on her by the boards, ice and Earth*D. No

Intuitive, even na?ve, knowledge and the matching of equations to physical situations can be useful resources, even for us. They must, however, be disciplined by more principled knowledge and reasoning.

The Matter & Interactions (M&I) Curriculum

The preceding problem is a typical physics problem in that it asks the student to explain or predict something about the structure or the behavior of a physical system, the skater, in some specific situation. Faced with such a task, what does a physicist do, when they are proceeding with care?

They appeal to fundamental physics principles and construct a model representation of the physical situation, they run the model to make their explanation or prediction and, finally, they assess the adequacy of the result.

M&I fosters the development of richly structured physics knowledge and the ability to use it flexibly and reliably by having students approach problem solving in this way. A handful of fundamental definitions and principles are the core of this knowledge structure.

The Momentum Principle ?????psys?psys,f?psys,i?Fnet,on sys by surr?t

The change in momentum of a system during a time interval Δtis equalto the net force exerted on the system by its surroundings. The time interval Δtmust be small enough that the net force is essentially constant during it.

The net force acting on a system at an instant is the vector sum of allforces exerted on the system by objects in its surroundings. The Energy Principle*

?Esys?Esys,f?Esys,i?Won sys by surr

The change in the energy of a system is equal to the work done it by its surroundings. The work done on a system …

The parallel form of these principles, repeated again in the form of the Angular Momentum Principle, and the analogous ways they are used when constructing models facilitates students’ learning and their use of what they’ve learned.

The Matter & Interactions (M&I) Curriculum

Based on their experience in a traditional HS physics course, the M&I approach to physics and to problem solving may not be what they are expecting.

They may, therefore, find it helpful for you to talk a bit about how

equations they may have memorized and used to answer questions about some kind of physical situation emerge in the new approach. Such equations are built efficiently and with physical meaning when we use our fundamental definitions and principles to construct a model of the situation of interest.

There are many opportunities to point out when this happens.

Modeling builds equations

that apply to specific

situations by applying

fundamental principles to initialfinal

statestatesystems involved and by

making situation-appropriate assumptions and idealizations.

Applying the energy principle to the system consisting of the skater and making the reasonable approximation that the frictional force exerted by the ice on the skater’s skates is negligible, we conclude correctly that no work is done on the skater in this case.

Applying the momentum principle to the system consisting of the skater and making the same approximation, we conclude that net force

exerted on the skater by her surroundings is equal to the force exerted on her by the boards and that her momentum changes accordingly. This implies a corresponding change in the skater’s translational kinetic energy expressed by the equation used earlier to “solve” the problem,

??122Fnet??RCofM??Ktrans?Msys?VCofM?V,fCofM,i?2a useful “theorem” of

Newtonian mechanics

When Possible Integrate Laboratory and Other Activities Model interatomic interactions usinga linear (spring) force law for small displacements from equilibrium separation, d, the atomic diameter.

The Model Solid

atomic diameter

from density

and molar mass

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