#visviva #energy #work #inertia #leibniz #newton #galileo

Energy is a key word that has been frequently used by physicists and non-physicists. Nevertheless, what is Energy? Is it a substance or not? Do electrical lines transport electirc Energy from on place to another? What is the Rest Energy of proton? What is the Self-Energy of electron? etc. To answer these questions, it is necessary to go to the roots.

Do you remember I said I will discuss energy, heat, and work in-depth in my recent talks? Today, I am going to talk about the related basic issues. Or should I say, I am going to start discussing the related issues, because it seem unlikely one talk is enough.

The world we have known is constantly in motion, from tiny biochemical molecules, to clouds in the atmosphere, and to the heavenly bodies such as the sun and the moon.

Indeed, every object is in motion, according to Galileo's relativity. But why? This is an old question which can be traced back to Aristotle in ancient Greek, one of students of Plato whose teacher was Socrates.

According to Aristotle, the reason why an object is moving is because some force is always acting on it. Further, he argued, the velocity is proportional to the force. Hence, motion is due to force. Sounds convincing, right? This could be the logic of introducing the so-called “living force” I am going to discuss today.

6.For nearly two thousands years after Aristotle, nobody had questioned this idea until Galileo grew up. Unlike others, Galileo investigated natural phenomena based on experiments.

8.One would say: simple, it is caused by friction. However, the young Galileo didn’t stop his thinking there. Instead, he asked himself: What would happen if the friction, including air resistance, were gradually diminished?

9.The conclusion drawn from his thought experiment was unexpected: an object would spontaneously keep its velocity forever.

10.So, Aristotle was wrong, a new concept was born, called, inertia, the most strange behavior of a non-living object. One may call it as stubbornness.

11.It was a paradigm shift in human’s history in understanding the nature. Motion just exists without any external force. The moving atoms, the moving planets and satellites, even the growth of trees, and out thoughts, are independent of the Aristotle’s force. That’s why one can think freely once all constrains are disposed.

12.I will return to Galileo's inclined motion experimenter because more new insights into motion can be gained from this simple experiment.

13. Galileo’s inertia was incorporated into Newton’s three laws of mechanics, the first law. Further, the relation between a change in velocity of an object and a force exerted was formulated by Newton, F=ma, where a=dv/dt is acceleration, known as the second law at the core of Newtonian mechanics.

14. I remember my teacher said: “Newton was merely puzzled by the First Push, because he believed that his mechanics based on his calculates can predict any mechanical motion given the First Push. That’s why he spent years to study alchemy and theology, apart from physics.”

15.However, another basic issue emerged during the 17th century from studying collisions between objects, such as this one demonstrated with this Newton’s cradle. As you can see, something must have been transferred among the metal balls, but what is this something?

16.Initially, the “something” was simply called as motion, but soon two seemly exclusive opinions were formed: one was mv, eventually known as momentum; (notice that both Descartes and Newton were in favor of using momentum, but Newton’s momentum is a vector, whilst Descartes's momentum is a scalar.) another is mv^2, advocated by Leibniz, Newton’s rival, as you might have known.

17.As early as 1638, Galileo wrote in his Dialogues Concerning Two New Sciences: “In the absence of resisting media, vertical fall is a uniformly accelerated motion, and hence the square of the speed acquired during fall is proportional to the height of fall.” So, one could argue that Leibniz was not alone.

18.In 1686, Leibniz published a short Note entitled:”A Brief Demonstration of a Notable Error of Descartes and Others Concerning of a Natural Law.” Obviously, the “others” here included Newton. In this Note, Leibniz first openly rejected the Quantity of Motion used by Descartes, namely, the product of mass and velocity.

19.In essence, Leibniz believed the world, or the whole universe, as a huge and sophisticated machine with a magical, God-given substance, the quantity of motion he preferred. He named the substance as vis viva in Latin, meaning: living force.