# Re-conceptualizing Introductory Physics Mark A. Peterson Mount Holyoke College May 9, 2007.

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Re-conceptualizing Introductory Physics Mark A. Peterson Mount Holyoke College May 9, 2007

Is there any alternative to …? Physics starts with Newton, and F=ma. Its subject is the motion of point particles.

An alternative view … Physics starts with Archimedes and Galileo Its subject is proportionalities in Nature One of its main goals and uses is common-sense estimation, using known proportionalities, dimensional analysis, and a few important data, including natural constants

Laboratory 1: Scaling in Bones A suggestion of Galileo: The length L and diameter D of homologous bones in animals should scale as D ~L The argument is that the required bone strength goes as L, but the actual bone strength goes as D. These should grow together. 3/2 3 2

Log-log plot of femur diameter D vs. length L

How is this starting point unusual? It is biological, and complex It is approximate, not precise It emphasizes proportionality (here in the form of a power law), via geometry (volume and area) It draws on history in a serious way, not as something merely supplementary It is an interesting, open-ended problem

Geometrical Optics Proportion and geometry, in a theory of how we see. Historical reference: perspective in Renaissance painting Mathematics: angles, small-angle approximation Utilitarian interest: optical instruments

Time Clocks: angular clocks; oscillator clocks; logarithmic clocks (decay) History: longitude, pendulum, GPS system Mathematics: sine and cosine as functions Mathematics: the effect of small perturbations (binomial approximation)

Equilibrium: forces and torques proportion again: Archimedes’ law of the lever Hooke’s Law, elasticity theory, geometrical factors (recall bones lab) Microscopic picture: springs in parallel and series, and the forces between atoms

Equilibrium: Energy An alternative conceptual picture of mechanical equilibrium: Minimization of potential energy. Kinetic energy and speed Conservation and non-conservation of mechanical energy: approach to equilibrium

Fluids Density, pressure: geometrical factors again, volume and area Archimedes’ principle, buoyancy Phenomenology of moving fluids Blood flow

Equilibrium: Thermal Temperature, Internal Energy Work (finally!) and conservation of energy 19 th century context : Rumford, Joule, Carnot Entropy and free energy Microscopic picture

Second semester More conventional, but still includes unconventional topics, like electrochemistry, and action potential in neuron Continues to draw heavily on the story line of physics: Young, Galvani, Volta, Oersted, Joule, Maxwell, Hertz, Planck, Einstein… Continues to emphasize continuum objects (like that most useful of concepts, energy current density, in W/m, i.e., brightness, loudness, “hotness”, etc., with frequent reference to sense perceptions.) 2

Student views “more coordination between physics, chemistry, and biology classes would be helpful, so that the information presented in each complements what’s taught in the others.” “I felt that dimensional analysis is the most useful thing that I learned in physics” “when we come across a concept that occurs in biology, such as enzymes (today), we should first discuss as a class how we know them in a biological sense AND THEN move on to …

Physics & Biology Making the Connections By Dana Alessi Spring Semester 2007

Physics as the Foundation “Many key advances in the biological sciences have been made possible by physics-based techniques. The future of biomedicine depends on collaboration between the two fields.” - Valerie Jamieson, Physics World, September 1999 http://physicsweb.org/articles/world/12/9/8

A Few Connecting Themes Energy & Heat Energy & Heat –Metabolism, ATP, brown fat, hibernation, homeostasis. Proportions Proportions –Anatomy Fluids, Poisseuille & Bernoulli, Viscosity, Osmolarity Fluids, Poisseuille & Bernoulli, Viscosity, Osmolarity –Transport in plants, circulatory system, osmolarity in homeostasis (kidney function), turgor pressure in plants. Optics Optics –Optometry, microscopes. Electrical Currents Electrical Currents –Nervous system, cell membrane transport, electrochemical gradients. Oxidation & Reduction Oxidation & Reduction –Electron transport chain in aerobic respiration (animals & plants!), photosynthesis. Waves Waves –Hearing & sight. –Why we have evolved to hear/see what we do & compare to other species. –Photons X-rays, cancer, bilirubin, vitamin D, melatonin. Radioactivity Radioactivity –Dosage, biological effects, sensitivity of nucleic acids. Young’s Modulus Young’s Modulus –Biomechanics, properties of different muscles & tissues in different species & their uses (structure & function!).

See section 8.17 “The Human Circulatory System” & section 8.18 “A Fractal Model of Circulation” (pages 290-301) of Physics in Proportion, Vol. I, Mark A. Peterson http://library.thinkquest.org/05aug/01883/introtocircman.gif http://www.biologycorner.com/resources/aortic_arch.jpg

http://www.discoveryfund.org/images/Eye_Anatomy-Anat.jpg

“Fish eyes are essentially spherical, unlike ours. Discuss the problem of the focal length of the fish eye, following the discussion in 3.9, not forgetting that, of course, fish eyes must work in water. How can we be sure that there is some essential structure inside the fish eye which is not part of the model in that Section? What could it be?” -Peterson, Physics in Proportion, Vol. I, p.115

See section 3.13.2 “The Microscope” & section 3.13.3 “Two lenses together” of Physics in Proportion, Vol. I, Mark A. Peterson (pages 93-96). http://www.ivyhall.district96.k12.il.us/4th/KKhp/Microbes/ProtistGraphics/microscopes/micros2.JPG

See chapter 16, “Bioelectricity, Electrochemistry” on page 485 & corresponding problems on page 514 Physics in Proportion, Vol. II, Mark A. Peterson http://imagecache2.allposters.com/images/pic/JAG/03-PS121-4~Nervous-System-Posters.jpg Electrical Charge & Potential http://www2.montana.edu/cftr/images/IonChannel2.gif

http://www.columbia.edu/cu/biology/courses/c2005/handouts/etccomplexes.jpg

http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig/35.07.jpg

http://www.midamericahearing.com/images/Ear%20Anatomy.GIF http://www.ucihs.uci.edu/hesp/images2/waveform.jpg

“In the last century it was noticed by nurses in France that newborns with a temporary jaundice condition, leading to a buildup of waste product called bilirubin in their blood, did better if their cribs were placed near an open window. Somehow sunlight accomplished something that artificial lighting in the room did not. This was later realized to be the photodissociation of bilirubin. Why would the two different light sources make a difference?” - Problem 19.3 on page 603 of Physics in Proportion, Vol. II, Mark A. Peterson

http://www.onlinetelemedicine.com/html/product/sam_images/X-Ray.jpg

How much of this works? Labs do get across the idea of VARIABLES that are functionally RELATED. For weak students, this is a big step, and maybe the most successful aspect of the course. Students are surprisingly tolerant of the use of history. Some students report more active thinking about their own perceptions of the world in physical terms, the kind of thing the course asks them to do again and again in problems.

What is class time for? I use just-in-time teaching. Students do a few short problems on a web page, I see their responses before class, and we go over them. I gradually realized that I didn’t have to lecture or derive things. Students were reading! We use class time for problems, group work, discussion.

To repeat! Physics starts with Archimedes and Galileo Its subject is proportionalities in Nature One of its main goals and uses is common-sense estimation, using known proportionalities, dimensional analysis, and a few important data, including natural constants

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