|The subtle Tower of Pisa experiment|
(Cf. discussion here, lab exercise here)
O -- OBSERVE apparent facts & patterns in nature6 --> A good place to begin is where a good slice of the Scientific Revolution began: with a swinging pendulum, and with experiments with lenses, with falling/rolling objects and basic optical instruments.
H -- HYPOTHESISE: what are the explaining “laws”?
(Here, we try to get at cause-effect links, models and theories that describe & explain patterns in the world.)
I & P -- I & P -- INFER & PREDICT: Based on the suggested “laws,” what will happen in other situations?
ET -- EMPIRICALLY TEST: We try to validate through experiments or observational studies, to see if we can reasonably trust the predictions. (We must always be open to correction: Science is provisional.)
a: Galileo, the key person involved, watched a pendulum in church as a student, and "timed" swings with his pulse; noticing that wider faster swings took more or less the same time as slower, shorter swings. (This holds if the swings are not more than about 6 degrees of arc. [See my short primer for teachers here, thoughts on insightful learning here and my preferred spiral curriculum framework here.])
b: Later on, he experimented with falling objects, and saw that a heavier object and a lighter one [once air resistance was factored out] will fall at pretty much the same rate, contrary to expectations. (With air resistance, there will be a slight delay of a lighter ball of the same size, e.g. wood/steel. Cf. modern exercise using modern technologies and software, here. This makes for a great class sized communal experiment.)
c: Hearing of telescopes -- probably from the Netherlands -- he built his Galilean telescope [with a diverging lens as eyepiece, giving an upright image]; and impressed his city with the commercial possibilities. Making such an instrument is a great, highly instructive and surprisingly do-able exercise:
d: Then, Galileo made a higher magnification [x 30] instrument and looked up at night, making astonishing discoveries about the universe. He also looked at the Sun -- we should NEVER do that, it burns holes in the retina of the eye [this probably contributed to his eventual blindness] -- and saw the phenomenon of sunspots. Instead, project the sun's image to a piece of card held behind a telescope.
e: He was probably aware of the astonishing behaviour of the Camera Obscura, whereby a pinhole in one end of an enclosure creates an inverted image on the opposite side, that can be seen through a translucent screen.
f: Later on, he experimented with heavy balls rolling in polished troughs and saw that if you have a U-shaped trough, the ball tends to rise to the original level. So he did a thought exercise: what if you made a perfectly smooth trough and then did not ever bring back up the far arm of the U? Would not the ball roll on forever . . . a form of the First Law of Motion: the principle of inertia by which what is at rest remains that way unless disturbed, and what is moving tends to keep its same motion going unless disturbed.
g: Similar exercises with inclined troughs point to the relationship between force and acceleration summed up in the Second Law of Motion: force is proportional to acceleration for the same mass.
h: Flicking one marble on a flat trough into another of the same mass will lead to the first stopping dead and the second heading off at the same speed. This points to the Third Law of Motion: when two bodies interact the forces of action and reaction are equal in size and opposite in direction.
(A great analysis exercise is of how we walk by pushing back on earth [50 -100 kg vs 6 * 10^24 kg], then how a car, a motor boat, a propeller aircraft, a jet plane, a rocket and a helicopter move.)
I: General Physics
II: Newtonian Mechanics
III: Energy and Thermal Physics
V: Electricity and Magnetism
VI: Atomic Physics
PS: For reference, I suggest Motion Mountain.