{"id":2772,"date":"2020-03-13T17:53:59","date_gmt":"2020-03-13T16:53:59","guid":{"rendered":"https:\/\/www.quantum-bits.org\/?p=2772"},"modified":"2022-08-12T17:13:27","modified_gmt":"2022-08-12T16:13:27","slug":"what-are-forces","status":"publish","type":"post","link":"https:\/\/www.quantum-bits.org\/?p=2772","title":{"rendered":"What are forces ?"},"content":{"rendered":"

This question stems from discussions at work<\/a> about the notion of “data gravity”, which, 10 years after its inception, seems to make a comeback and draw some kind of vague buzz within the Data & IT community. It quickly turned out that this concept – though appealing from afar – is one of these so many crackpot<\/a> concepts that Wolfgang Paul<\/a> would call “not even wrong<\/a>“.<\/p>\n

Indeed, the concept relies on misconceptions about sciences & physics in general, and the way (gravity) forces works and behaves in particular. McCrory’s “gravity formula” (which, somehow, tries to mimic Newton’s law of gravity) reminded me of one of my high school physics teacher’s favorite saying: “don’t mix elephants and wild strawberries in a formula !” (“Vous m\u00e9langez les \u00e9l\u00e9phants et les fraises de bois !<\/em>“).  <\/p>\n

So, let’s forget “data gravity” and … let’s go back to basics: what are forces ? <\/p>\n

\"\"<\/p>\n

What are forces ?<\/strong><\/p>\n

Let’s first have a look at the etymology of the word: “force<\/em>” comes from Middle English “force<\/em>“, which comes from the Old French word “force<\/em>” … which comes for latin “fortia<\/em>” : strong<\/em>, brave<\/em>, courageous<\/em>. <\/p>\n

By extension, “force<\/em>” describe any capacity of exercising an influence or producing an effect. “Force<\/em>” is therefore a relatively ill-defined concept. But, at the same time, is also a highly intuitive notion: in this definition, “force<\/em>” is related only to strength<\/em>, and strength is something that anybody can immediately feel<\/em> and experience<\/em>.<\/p>\n

Historically speaking, it took a long time to clearly define the concept, by relating forces not to strength, but to motion<\/i>. <\/p>\n

Following this path, philosophers such as Aristotle<\/a> or early scientists such as Archimedes<\/a> retained nevertheless fundamental errors in understanding force, due to an inadequate view of frictions and of the nature of natural motion: <\/em>the belief – at the time – was that a force is required to maintain<\/em> motion (even at a constant velocity).<\/p>\n

Aristotelian physics began facing criticism in medieval science, but its shortcomings would not be fully corrected until the 17th century with physicists like Galileo Galilei<\/a> or Sir Isaac Newton<\/a>: a force is any interaction that will change the motion of an object<\/em><\/strong>. Using mathematics, Newton formulated his laws of motion<\/a>, that were not improved for nearly three hundred years.<\/p>\n

This all changed<\/strong> in the early 20th century, where observations<\/strong> lead physicists to completely new insights, giving birth to relativity<\/a> and quantum mechanics<\/a>. <\/p>\n

Skipping Aristotelian physics, in the next paragraphs, we will explore the notion of force, within the historical framework of Newtonian physics and within the frameworks of today’s physics.<\/p>\n

Newtonian physics<\/strong><\/p>\n

Laws of movement were set out in 1687 in Newton’s masterpiece “Philosophiae naturalis principia mathematica<\/a>“. These three laws are the principles underlying the movement of bodies (i.e., what is now called classical mechanics). They describe the relationship between a body and the forces acting upon it, and its motion in response to those forces. They are completed with the law of universal gravitation (i.e. what is now called classical gravity).<\/p>\n

Newton’s first law<\/strong> is the following (inertia principle): “Every body persists in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed.<\/em>”<\/p>\n

In other terms, a particle not subject to forces moves (related to inertial frame) in a straight line at a constant speed. This is known as uniform motion<\/strong>:<\/i><\/p>\n