In physics, in particular in special relativity and general relativity, a four-velocity is a four-vector in four-dimensional spacetime that represents the relativistic counterpart of velocity, which is a three-dimensional vector in space. Physical events correspond to mathematical points in time and space, the set of all of them together forming a mathematical model of physical four-dimensional spacetime. The history of an object traces a curve in spacetime, called its world line. If the object has mass, so that its speed is necessarily less than the speed of light, the world line may be parametrized by the proper time of the object. The four-velocity is the rate of change of four-position with respect to the proper time along the curve. The velocity, in contrast, is the rate of change of the position in (three-dimensional) space of the object, as seen by an observer, with respect to the observer's time. The value of the magnitude of an object's four-velocity, i.e. the quantity obtained by applying the metric tensor g to the four-velocity U, that is ||U||2 = U ⋅ U = gμνUνUμ, is always equal to ±c2, where c is the speed of light. Whether the plus or minus sign applies depends on the choice of metric signature. For an object at rest its four-velocity is parallel to the direction of the time coordinate with U0 = c. A four-velocity is thus the normalized future-directed timelike tangent vector to a world line, and is a contravariant vector. Though it is a vector, addition of two four-velocities does not yield a four-velocity: the space of four-velocities is not itself a vector space. (Wikipedia).
What is a Four-Vector? Is a Spinor a Four-Vector? | Special Relativity
In special relativity, we are dealing a lot with four-vectors, but what exactly is a four-vector? A four-vector is an object with four entries, which get transformed and changed in a very special way after we change our frame of reference. More precisely, a four-vector transforms like a (1
From playlist Special Relativity, General Relativity
For more information about Professor Shankar's book based on the lectures from this course, Fundamentals of Physics: Mechanics, Relativity, and Thermodynamics, visit http://bit.ly/1jFIqNu. Fundamentals of Physics (PHYS 200) The discussion of four-vector in relativity continues but this t
From playlist Fundamentals of Physics with Ramamurti Shankar
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For more information about Professor Shankar's book based on the lectures from this course, Fundamentals of Physics: Mechanics, Relativity, and Thermodynamics, visit http://bit.ly/1jFIqNu. Fundamentals of Physics (PHYS 200) The four-vector is introduced that unifies space-time coordinate
From playlist Fundamentals of Physics with Ramamurti Shankar
What is the 4th Dimension REALLY? - 4D Golf Devlog #2
A more practical explanation for those interested in exploring 4D spaces. For those not already familiar with basic 4D concepts, here's some videos I can recommend: "Visualizing 4D Geometry" https://www.youtube.com/watch?v=4URVJ3D8e8k "The things you'll find in higher dimensions" https:/
From playlist 4D Golf
The Definition of a Linear Equation in Two Variables
This video defines a linear equation in to variables and provides examples of the different forms of linear equations. http://mathispower4u.com
From playlist The Coordinate Plane, Plotting Points, and Solutions to Linear Equations in Two Variables
Acceleration in Special Relativity | Four-Acceleration
In this video, we will explain acceleration in special relativity. In classical mechanics, acceleration is defined as the time derivative of the velocity vector. In special relativity, we use a similar equation, but instead of a time derivative, we use a derivative with respect to the pr
From playlist Special Relativity, General Relativity
Can You Solve This THREE Dimensional Physics Problem?!?? #Physics #Mechanics #Engineering #3D #NicholasGKK #Shorts
From playlist General Mechanics
System of Equations with Three Equations and Three Variables
Please Subscribe here, thank you!!! https://goo.gl/JQ8Nys System of Equations with Three Equations and Three Variables
From playlist Systems of Equations
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From playlist Physics
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In this video David rapidly explains all the concepts in 1D motion and also quickly solves a sample problem for each concept. Click on and keep an eye on the side scroll to go to the topic you want and to see how far along you've made it in the review video. Here's a link to download the
From playlist Review for AP Physics 1 exam | AP Physics 1 | Khan Academy
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Lecture 6 of Leonard Susskind's course concentrating on Quantum Entanglements (Part 3, Spring 2007). Recorded May 14, 2007 at Stanford University. This Stanford Continuing Studies course is the third of a three-quarter sequence of classes exploring the "quantum entanglements" in modern
From playlist Lecture Collection | Quantum Entanglements: Part 3 (Spring 2007)
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Download Packet: https://goo.gl/Cjrhyr ================================= AP Calculus AB / IB Math SL Unit 5: Existence Theorems and Particle Motion Lesson 5: Particle Motion Practice =================================
From playlist AP Calculus AB
Jet Aircraft Propulsion by Prof. Bhaskar Roy and Prof. A. M. Pradeep, Department of Aerospace Engineering, IIT Bombay. For more details on NPTEL visit http://nptel.iitm.ac.in
From playlist IIT Bombay: Aerospace - Jet Aircraft Propulsion (CosmoLearning Aerospace Engineering)
Average velocity for constant acceleration | One-dimensional motion | Physics | Khan Academy
Calculating average velocity when acceleration is constant. Created by Sal Khan. Watch the next lesson: https://www.khanacademy.org/science/physics/one-dimensional-motion/kinematic-formulas/v/acceleration-of-aircraft-carrier-takeoff?utm_source=YT&utm_medium=Desc&utm_campaign=physics Miss
From playlist One-dimensional motion | AP Physics 1 | Khan Academy
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Visit http://ilectureonline.com for more math and science lectures! To donate: http://www.ilectureonline.com/donate https://www.patreon.com/user?u=3236071 A proton, a deuteron and an alpha-particle are moving with the same momentum in a uniform magnetic field. The ratio of magnetic force
From playlist JEE (MAIN) PHYSICS E&M ELECTRICITY AND MAGNETISM
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From playlist Vector Valued Functions
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From playlist Lecture Collection | Quantum Entanglements: Part 3 (Spring 2007)
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Please Subscribe here, thank you!!! https://goo.gl/JQ8Nys Vector with Magnitude 4 in the Direction of u = (0, 3). We find the vector v with ||v|| = 4 that has the same direction as u = (0, 3).
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MIT المحاضرة التاسعة من مساق "الميكانيك التقليدي" من جامعة "إم آي تي" للبروفيسور والتر لوين وهي عن: مراجعة ما قبل الامتحان الأول بالإضافة للفيديو هناك ملفات مرفقة على موقعنا الالكتروني https://shamsunalarabia.net/courses/ﺍﻟﻤﻴﻜﺎﻧﻴﻚ-التقليدي/ رابط المساق https://youtu.be/FNooVZcJvG0?list=PL
From playlist 8.01 Arabic Subtitles