What does "sub i" mean?


by The riddler
Tags: derivitive, equation, kinetic energy, time
The riddler
The riddler is offline
#1
Jul2-10, 03:03 AM
P: 94
Im not 100% sure what the "sub i" symbol means when next to values such as Velcoity and Aceleration, here is and example of it being used in this equation for the time derivitive of kinetic energy.

Ek(d/dt) = Σm*Vi*Ai

Ek = Kinetic energy
d = Derivitive
t = Time
V = Velocity
A = Acceleration
sub i = ???

Can someone please tell me what it stands for,

Thanks for any replies :)
Phys.Org News Partner Physics news on Phys.org
Physicists design quantum switches which can be activated by single photons
'Dressed' laser aimed at clouds may be key to inducing rain, lightning
Higher-order nonlinear optical processes observed using the SACLA X-ray free-electron laser
Pengwuino
Pengwuino is offline
#2
Jul2-10, 03:11 AM
PF Gold
Pengwuino's Avatar
P: 7,125
The subscript 'i' refers to the component x,y, and z. It is an index that goes from 1 to 3, 1 = x, 2 = y, 3 = z that is used for the sum. In this case, it means the sum of [tex]mV_x A_x + mV_y A_y + mV_z A_z[/tex] in component terms.

In more advanced studies, you'll see the summation term dropped and when you see a repeated index such as the one you have, that kind of sum is implied. On the other hand, if you have something like [tex]A_i B_j[/tex] where A and B are just two indices, the index runs from 1 to 3 on both i and j so you get 9 terms that include [tex]A_1 B_3 , A_2 B_3 , A_1 B_1 [/tex] etc etc.


Register to reply

Related Discussions
Learning device, help me expound: on Faraday's choice of "ion", and "unionized" Electrical Engineering 2
Difference between "Identical", "Equal", "Equivalent" Calculus & Beyond Homework 9
Anyone familiar with "centrifugal potential" and "brachistochrone" in polar coords? Advanced Physics Homework 7