The Nature of Scientific Inquiry Observe Describe Explain

A Silly Example Observe: Look at the man’s picture. Describe his skin tones Explain: How might he have acquired that look? {mechanism}

What tasks do scientists do? Observe some natural phenomenon {i.e. measure two or more physical quantities} Describe the relationship among the physical quantities {often this can be expressed as a mathematical formula} Explain the relationship {e.g. a cause and effect “mechanism”}. Explanation must be consistent with other accepted explanations

Scientific Inquiry Terms An observation is often called an experiment {when physical quantities are controlled} A description of the relationship among two or more physical quantities is called a law An explanation of the causes of the relationship is called a theory

I hate the 5-step scientific method!!! The 5-Step Scientific Method

“Many [of the Physics textbooks we reviewed] teach the “scientific method” illustrated step-by-step. The idea that there is such a method, or that memorizing the steps can be helpful, is [an abomination] to practicing physicists.” Dr. Clifford Swartz et al., in The Physics Teacher, May 1999, page 297

But Wait, Dr. B! You presented Observe, Describe, Explain as if it was a sequence! True, but I’m just doing that to organize my lessons. I like that order because it is different than how I “learned” Physics back in the day.

“Science walks forward on two feet, namely theory and experiment. Sometimes it is one foot which is put forward first, sometimes the other, but continuous progress is only made by the use of both - by theorizing and then testing, or by finding new relations in the process of experimenting and then bringing the theoretical foot up and pushing it beyond, and so on in unending alternation” Dr. Robert Millikan, Nobel Prize in Physics: 1923

“I venture to think that the people who talk most about [the Scientific Method] are the people who do least about it… Scientific method is something talked about by people standing on the outside and wondering how the scientist manages to do it…In short, science is what scientists do, and there are as many scientific methods as there are individual scientists.” Dr. Percy Bridgman, Nobel Prize in Physics, 1946

The Three Pillars of Gen Physics Make accurate measurements (observations) of physical quantities – including units! Combine these physical quantities in mathematical formulas (descriptions) and be able to manipulate these algebraically. Learn the concepts and theories (explanations) and understand how they are consistent with relevant observations and laws.

Different Types of Models Conceptual Model: All in your mind, like Imagine the conditions inside a tornado… Physical Model: Such as a scale model, or a Free-Body Diagram. Mathematical Model: the equation describing the relationship between two or more physical quantities (e.g. PV=nRT). All models represent some aspects of a real system (too complex to represent all of it).

Counterexample (NOT science) The Dresden Maya Codex Observations of the planet Venus Description: mathematical formula could accurately predict future positions of planet Venus based on the observed patterns in the data. Explanation? Even the Mayans wanted a mechanism to explain the observations. See Encyclopedia Brittanica at

Counterexample (NOT science) Mayan Explanation: The god Kukulcan traveled around the heavens with his brother, the Sun (FAIL!!). Science is for the natural world, not the supernatural! Also, this explanation does not generate any mathematical relationship! So it’s not compatible with the description. See Encyclopedia Brittanica at

Modeling the Solar System Observations: By the early 1600’s the (heliocentric) orbits of the (six) planets were accurately known. Johannes Kepler discovered a mathematical model relating radius and period of planetary orbits. Now called Kepler’s 3 rd Law: P 2 = kR 3. Kepler’s theories were unsuccessful: orbital radii modeled by 6 celestial spheres separated by 5 Platonic Solids; planetary motion explained by solar magnetism (Sun as spinning magnet). Neither part is compatible with observations!

Modeling the Solar System (cont.) Titius-Bode Law: (n+4)/10 {for n = 0, 3, 6, 12…} successfully described spacing of known planetary orbits in “Law” successfully predicted orbital radius of “missing planet” between Mars and Jupiter. Description is not precise, and it breaks down for Neptune; also, no physical mechanism has ever been found to explain it (just a numeric coincidence).

The Complete Package Newton’s Gravitational Theory unites it all: (“gravity causes orbital motion”) So, but Thus or Theory is consistent with observations & descriptions.