Can we differentiate with respect to a vector?

  • #1
KnightTheConqueror
9
7
We know that a = vdv/dx
But is it applicable in only one dimensional components or is this actually a vector equation? If so then how do we exactly differentiate with respect to position 'vector'?
 
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  • #2
Thanks for answering, but I know that I can resolve it into components and solve. My problem is not that I am unable to use that equation in 3D. Rather, I am just curious whether we can write that equation as an vector equation directly without resolving.

Let me elaborate...

v = u + at here, although we can apply this equairon to x, y, z component separately and then add them but resolving into components is just something to make our work easier. v = u + at is still a vector equation and we can solve it using other methods of vector too for example geometry.
Likewise, I can apply a = vdv/dx to x, or vdv/dy to y
But
Can we just write that equation in vector form without needing to resolve into one dimensional components? Can we say that acceleration vector = velocity vector times d of velocity vector upon x of position vector.
If so then what exactly do we mean by differentiating with respect to a vector?
 
  • #3
KnightTheConqueror said:
We know that a = vdv/dx
But is it applicable in only one dimensional components or is this actually a vector equation? If so then how do we exactly differentiate with respect to position 'vector'?
Let ##s## denote arc length along the trajectory of the particle. Consider the velocity of the particle as a function of arc length: ##\vec v(s)##. Use the chain rule to express the acceleration as ##\vec a = \dfrac{d\vec v}{ds} \dfrac{ds}{dt}## and note that ##\dfrac{ds}{dt}## is the speed ##v## of the particle. So, ##\vec a = v\dfrac{d\vec v}{ds}##.
(This expression is undefined at points of the trajectory where ##v = 0##, just as the 1-D expression ##a = v \dfrac{dv}{dx}## is undefined when ##v = 0##.)
 

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