Let vec(a) , vec(b) in RR^3 be given, Consider the curve vec(r) (t)=vec(OP)_0+t vec(a) +t^2 vec(b) , t in RR Find the curvature of the curve at vec(r) (0).

Nikolai Decker

Nikolai Decker

Answered question

2022-10-21

Let a , b R 3 be given,
Consider the curve r ( t ) = O P 0 + t a + t 2 b , t R
Find the curvature of the curve at r ( 0 )
I have just started learning about arc-lengths and paremetrizations, and I have no clue how to approach this question. I've tried splitting each vector in the function to its components (e.g. a ( a 1 , a 2 , a 3 ) ), but I can't progress any further. I'm wondering how to incorporate the curvature formula for this question;
r ( t ) × r ( t ) | r ( t ) | 3
Any help would be greatly appreciated.

Answer & Explanation

bibliothecaqz

bibliothecaqz

Beginner2022-10-22Added 12 answers

The formula is
κ = | | r ˙ × r ¨ | | ( r ˙ r ˙ ) 3 / 2
Your notation is really unfortunate, since the vector a usually denotes the acceleration vector, i.e. r ¨ ,, but I'll stick with that bad notation.
r ˙ = a + 2 t b
r ¨ = 2 b
At  t = 0 , r ˙ = a ,
κ = 2 | | a × b | | ( a a ) 3 / 2 .

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