**Galileo Galilei**

*"Galileo ... is the father of modern physics -- indeed of modern science" - Albert Einstein ( 1879 - 1955 )*

Galileo Galilei ( Tuscan - Italian, 1564 - 1642 ) by Giusto Sustermans

From **"***Discorsi e dimostrazioni matematiche, intorno à due nuove scienze***"** ( Discourses and Mathematical Demonstrations Relating to Two New Sciences, Third Day: Naturally Accelerated Motion )^{∗}, 1638, by Galileo Galilei, his final work in physics covering his preceding 30 years, stated

**"** ... that in equal times bodies moving at different speeds cover distances in proportion to their speeds**"**

and

**"**A motion is said to be uniformly accelerated, when starting from rest, it acquires, during equal time-intervals, equal increments of speed**"**

wherein he experimentally arrived at his famous **"**Law of Falling Bodies**"** equation:

In the experiment, Galileo presumably used a water clock comprised of an **"**extremely accurate balance**"** to measure the amount of water collected and hence to measure durations of elapsed time during which balls of different weights [ and therefore different masses ] were rolled along an inclined ramp in order to study the effects of earth's gravity. Out of these experiments he derived his famous **"**Law of Falling Bodies**"**:

As a result of the above equation, Galileo Galilei was the first to experimentally make the attempt to determine the value of of or simply , the standard acceleration of earth's gravity [ latin: *gravitas*, *gravis* ( heavy ) ] effect at sea level, where the modern accepted value is 9.80665 ( meters / second^{2} ). Please note that is a vector quantity owning to the fact that it points between the centers of any two masses which makes manifest the appearance of gravity.

Nevertheless, Galileo's two major contributions to modern physics were the **"**Law of Falling Bodies**"** and the **"**Law of

Inertia**"**.^{∗∗∗}

**Thomas Harriot - Preceded Galileo in Celestial Observations Using a Telescope**

Before Galileo Galilei's telescope peered at the Moon by several months earlier, there was English Thomas Harriot ( 1560 - 1621 ), astronomer, mathematician and celestial cartographer who first drew an extra-terrestial map of something outside of the bounds of earth. Harriot did this in July, 1606 of the Moon and continued to draw ever more detailed maps of lunar surface and craters whose accuracy remained unchallenged for several decades thereafter.

**One of Only Two Extant Galileo Telescopes Arrives in Philadelphia**

The James Webb Space Telescope and Sunshield: Extraction and Deployment - launch date: 2014

^{∗}

note: English source translation: Henry Crew and Alfonso de Salvio - Macmillan, 1914

^{∗∗∗}

note: latin: *in* + *ars* = *iners*, meaning unskilled or artless whereas Kepler used the word for bodies at rest and Newton gave the word 'inertia' its modern mathematical meaning of bodies in undisturbed, straight - line motion unless subject to forces of acceleration.