Galilean Relativity

Ideas that changed our notion about the Universe.

1. Aristotle Fallacy; A notion that objects need force for their movement. It contradicts the idea of inertia. Newton corrected this by introducing the first law, things continue in their state of motion, a quality called as inertia, without requiring force and the motion changes due to application of force.

2. Earth is flat; that there is a boundary where you fall off its edge. [I am not going to explain or tell you how and when we found this was a horrendously hilarious and misleading notion we had. But it might have been used in the past by parents to discipline their teen-age kids. Don’t go out, you will fall off earth. That would have kept them in check.]

3. Rotational Dynamics; Earth is accelerating in a near circle in addition to about itself, so additional forces are acting that changes our observation about the world. Newton tried to understand this (not successful) in his last days, by rotating a bucket full of water, his laws could not explain the effects observed. His laws needed to be modified slightly. The same thing makes objects feel weightless by a given amount if they are accelerating towards a gravitational field (eg merry go round, satellites) This is the basis of many works of Einstein. First came Mach’s Principle which says observations made from objects that are accelerating in circular paths are to be corrected by fixing frames of references to stars that are so far away that the rotational motion is neglected. [if you shake your head while looking at stars and shake your head by looking at nearby objects such as a light post, evidently the light post shakes more and the stars less]. This helps in correcting observed phenomena from earth. Earth moves at 30 kms/second wrt sun …

Still some gravity !!

So talking about gravity fondly I have made a remark “Its not gravity that makes you fall”. You would be shocked as if you fell down but its not due to gravity but something else is at work, Am I a Physicist propounding a phantom theory? The actual statement I made is “Its not gravity that makes you fall, it only makes you fall FASTER”. That was known to Galileo, which we often very conveniently forget and make an erroneous statement that things fall because of Gravity. So it caters to the law of inertia also. So satellites would still fall irrespective of the absence or presence of Gravity. (although the inertia would mean they would be at absolute rest if we do not take into account enough of its past when something had hit it harder to slow it down or sped it up, in any case when enough history has been allowed to see that no forces or extra actions were disturbing its inertia, IT MUST BE MOVING AT UNIFORM MOTION without any debt to a force-bank called Gravity. If Gravity isn’t there the inertia is still the same and it would continue to be moving at the same speed, which as a specific possibility be ZERO)

So apart from the fact that Gravity only causes us to fall faster its also an erroneous fact to say: Gravity is caused by Masses. Or its innocuous looking twin-statement masses attract masses and thats called Gravity. It has two basic history why its often thought or said so. 1. History of how theory of Gravity developed. 2. History of how Gravity was taught.

How to add speeds; Galileo and Einstein won’t agree.

How to calculate the speed of anything, when their speed becomes closer to the speed-of-light. 
This article was originally a comment in the linked article;  Why Nothing Moves Faster Than Light.

— In order to correct the comment I have made earlier  ” unless something is completely mass-less in its rest-frame ” I also add the following. This is a fact which I have realized lately — or rather trapped myself to commit an inconsistent remark, by following the same comment in making other remarks elsewhere. 

But it’s better late than never to realize; when something is mass-less, it will never have a rest-frame, because by Einstein’s transformation rules, known as Theory of Relativity, to be consistent, a mass-less particle will always move at the speed of light c, no matter which frame we are looking at it from. This then leads to the velocity addition formula of Einstein.

Now we will discuss in a slightly more detail the two kind of velocity addition formula, one prior to Einstein and one that came from Einstein’s work. 

Prior to Einstein. 
According to Newton and Galileo ( Galileo Project ), known by a name Galilean Relativity, the following follows; if C moves at speed