Velocity is a vector in Newtonian mechanics

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SUMMARY

The discussion confirms that velocity is indeed a vector in Newtonian mechanics, as demonstrated through the application of vector analysis from Arfken and Weber's "Mathematical Methods for Physicists, 5th edition." The transformation of the position vector, represented as ##\vec X##, follows the rule ##X_{i}^{'}=\sum^3_{j=1} a_{ij}X_{j}##, and upon differentiation with respect to time, the velocity vector transforms according to ##\dot{X}_{i}^{'}=\sum_{j=1}^3 a_{ij}\dot{X}_{j}##. This confirms that the time derivative of the position vector maintains the properties of a vector under coordinate transformations.

PREREQUISITES
  • Understanding of vector analysis as presented in "Mathematical Methods for Physicists, 5th edition."
  • Familiarity with Newtonian mechanics and the concept of vectors.
  • Knowledge of tensor analysis and its application in physics.
  • Basic calculus, specifically differentiation of vector functions.
NEXT STEPS
  • Study the transformation properties of vectors in different coordinate systems.
  • Explore the implications of vector calculus in Newtonian mechanics.
  • Learn about tensor analysis and its applications in physics.
  • Review advanced topics in vector analysis, particularly in the context of physics.
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Students of physics, particularly those studying mechanics, mathematicians interested in vector analysis, and educators looking to deepen their understanding of the relationship between vectors and physical quantities.

BookWei
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I studied the vector analysis in Arfken and Weber's textbook : Mathematical Methods for Physicists 5th edition.
In this book they give the definition of vectors in N dimensions as the following:
The set of ##N## quantities ##V_{j}## is said to be the components of an N-dimensional vector ##V##
if and only if their values relative to the rotated coordinate axes are given by
$$V_{i}^{'}=\sum_{j=1}^N a_{ij}V_{j},\;i=1,2,...,N$$
From the definition of ##a_{ij}## as the cosine of the angle between the positive ##x_{i}^{'}## direction
and the positive ##x_{j}## direction we may write (Cartesian coordinates)
$$a_{ij}=\frac {\partial x_{i}^{'}} {\partial x_{j}}$$

Can we use the same mathematical method (or tensor analysis) to prove the velocity is a vector in
Newtonian mechanics?
Many thanks!
 
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BookWei said:
Can we use the same mathematical method (or tensor analysis) to prove the velocity is a vector in
Newtonian mechanics?
Why not? If you have a position vector ##\vec X## that transforms according to ##X_{i}^{'}=\sum^3_{j=1} a_{ij}X_{j}##, then when you take the time derivative, ##\dot{X}_{i}^{'}=\sum_{j=1}^3 a_{ij}\dot{X}_{j}##. This says that ##\dot{\vec X}## transforms as a vector.
 

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