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In order to understand relativity and its concepts, it is mandatory to attain general knowledge of physics. Throughout this lesson we will touch upon the main principles and laws of physics which led the scientists to the theory of relativity. Newton's three laws, concepts such as velocity, acceleration, force, mass, etc. all act as a basis to the theory of relativity. The Magnitudes As we said in the Vectorial Analysis lesson, there are two kinds of magnitudes: vectorial magnitudes and scalar magnitudes. In this part we will study the main vectorial magnitudes used in the developement of mechanics which later lead to relativity, these magnitudes are: velocity, acceleration and force. Also we will stablish the concepts of distcane and mass. The First Magnitude: Velocity Velocity is the time a particle or object takes to travel a certain ammount of distance. That is why it is always expressed in distance/time units (i.e. [meters/second]). Velocity is probably the easiest to learn of the magnitudes because it is one we're used to. Now let's think a little, where did [m/s] or [km/h] came from? It is rather simple. To obtain a value of velocity we divide the distance by the time. So for example, if a car travels 8 meters in 2 seconds, we would have:
So this car would travel 4 meters every second, that is its speed. Now what would happen if there were two cars, facing one another, both with the same reading on the speedometer. Would they have the same velocity? We had a similar question in the lesson about vectorial analysis, the answer is no. The value of the velocity is known as "scalar velocity" or "speed", but this is just a part of the magnitude since this magnitude is a vector it also has a direction. So for the two cars to have the same velocity they would have to have the same scalar velocity and the same direction. The magnitude that changes velocity is known as acceleration.
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