Models, Interaction and Energy - Powerful Ideas for Teaching Science

1. Models

o working models - particle model, rigid body model for chair or table, sphere model for Earth, molecular model for gases…This is a model in which we visualize something that "works" (usually invisibly, or behind the scenes) that produces the effects that we see. This is usually a representation in our minds that is patterned after a system in the real world, but we use the flexibility of our ideas to make the model fit the physical reality or data as closely as possible.

o analogue model - example (Fill it out yourself - see below for "answers")

Human Circulatory System: Hot Water Heating System:

veins & arteries : (blood vessels) __________

__________ : water

oxygen : __________

__________ : pump

lungs : __________

__________ : radiators

__________ : thermostat

__________ : overflow tank

blood pressure : _____??_____

white blood cells : ______??____

carbon dioxide : ______??____

kidneys : ____??______

intestine : ____??______

This kind of analogue model allows us to investigate a system without touching it - we may not be able to experiment directly on a human being but we can more easily do this on a hot water system.... The analogy also can alert us to something in one system that is not evident at first glance in the other system. BUT we must be constantly aware of the possible limitations in the analogy - the characteristics and ways of operating appropriate to one system may simply not apply to the other system - or, most interestingly, we must think about them and apply them in a different way in order to get the same result. This is particularly revealing in 'scale' models, which are in a sense a certain kind of working model - we have to be very careful about increasing the size of a model - they may look the same geometrically, but they don't work the same physically, and the ways in which they change can be subtle indeed, though usually subject to analysis and control. Smaller-sized "scale models" are often used in engineering, and sometimes in science, to attempt to find out about how the full-sized object (for example a bridge) will work when it is actually built. Computer models are, of course, now widely used.

o mathematical model - the synthesis of data from the "real world" into a clean, economical mathematical model that summarizes and includes all of the previous phenomenological observations, that can be used to predict the results of experiments that have not yet been performed, and that provides a conceptual basis for solving additional problems and for building new theories has been, essentially, the goal of physics and the dream of physicists since Newton (indeed, since Archimedes). However, the extent to which, and the point at which, mathematical models should be part of courses in science is something that one can debate, and that teachers should consider very carefully.

o Issues for all models -

§ assumptions,

§ limitations and strengths,

§ where they can, and cannot, be used.

2. Interaction Concept.

Motivation - Newtonian point of view and concepts (especially acceleration, mass and force) present high abstract hurdle for beginners. Interaction is a more general, global concept which can then be developed and differentiated to evolve the specific and focused concepts required by Newtonian mechanics.

Requires change to "modern scientific viewpoint":

· Seek explanation of change in influence of (interaction with) outside objects, rather than in "nature" of things, inherent power or "desires," or anthropomorphic projection.

· Inertia of motion - relationship between amount of friction and change in object's speed. Reducing friction means object changes speed less and less. When object goes up slope, its speed decreases. When object goes down slope, its speed increases.

· Experiencing physical interactions with heavy, smoothly-rolling objects - interaction to speed up & slow down, motion in absence of interaction.

· Direct experiences with objects' motion after being constrained in circular path - does it move in straight line or continue in curved path?

· Thermal interactions

· Other interactions - dissolving salt or sugar, Alka-Seltzer in water…

· Interaction-at-a-distance - magnetic, electric and gravitational fields, electro-magnetic waves.

3. Energy Concept.

Can start with food, gas mileage, analogy with money and bank account.

Emphasize energy storage and changes involved when energy is stored rather than merely naming forms of energy.

Passive coupling elements

Degradation of energy

Conservation of energy.

ALL of the above can, and I think should, be part of science courses from elementary school onward!

Now - how about physics courses:

4. Force is a way to describe physical interactions

- where objects change state of motion. This involves thinking about the "point mass" model - the point wherer the force is applied. Definition in terms of spring scale. Always have two objects involved.

5. Distinction between inertial and gravitational mass.

6. Newton's Laws....