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# Special Vs. Galilean Relativity

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Sections
Inertial Reference Frames
Special Vs. Galilean Relativity
Consequences of Relativity
Lorentz Transformations

Concept #1: Special Vs. Galilean Relativity

Transcript

Hey guys, in this video we're going to start talking more specifically about special relativity and we're going to compare it to something called Galilean relativity which is the theory of relativity in classical physics. Alright let's get to it now like I said Galilean relativity is our classical theory of relativity it was established as the name applies by Galileo Newton really put it on solid foundation and credited Galileo for really getting the theory started. In Galilean relativity the problems are very very simple if you have some frame moving let's not talk about frames just yet let's talk about a classic physics problem like an airplane.

So you have some sort of airplane moving with a velocity V through the wind so the wind itself is moving with the speed U so let me call this V prime actually because that's the speed of the that's the velocity of the airplane with respect to the air when you're in an airplane you're often measuring your airspeed sorry you're almost entirely measuring your airspeed unless you have a computer that can calculate ground speed because air speed is what actually matters in an airplane because how quickly the air is moving over the wings is what determines whether or not you fly it doesn't matter how quickly you're moving over the ground it matters how quickly you're moving through the air so the air itself is moving with a velocity of U relative to the ground so the moving frame in this case is going to be the air so the velocity of the airplane with respect to the air is the velocity in the moving frame and the velocity in the lab frame which is just the velocity of the airplane over the ground is going to be the sum of those two velocitys and you can see if you imagine it if the airplane is moving with respect to the air forward but the air is pushing the airplane to the side you can see that the airplane relative to the ground is actually going to be moving at an angle because in the pilot's mind the air is stationary right the plane just cutting through the air and the air is stationary but the air is actually moving with respect to the earth so the actual medium that the plane is moving through is moving and carrying the plane sideways this is what a lot of people just refer to this equation right here as the addition of velocities its simple additive simple addition of velocities in Galilean relativity but this isn't true for special relativity and we'll see the equation that replaces this but it's important to realize right away that Galilean relativity has a completely different ramifications than special relativity the most important one occurs when you're near the speed of light. So if this airplane for some reason was moving at you know the speed of light and the wind was pushing it forward at half the speed of light using Galilean relativity if you measure the airplane speed going overhead it would be moving at one and a half times the speed of light and this violates special relativity because nothing can move faster than the speed of light.