# rms formula

#### mentaaal

Joined Oct 17, 2005
451
Hey guys, I have been pondering this since i was first introduced to it years ago in school so i hope one of you can shed some light on this. In a lot of root mean square formulas like the ones used in coordinate geometry, statistics and the rms formula in electronics, howcome we cant just square each number and square root it (to remove the negative sign) like for example ithe rms formula at http://en.wikipedia.org/wiki/Root_mean_square. Why do we have to find the square root of the demonimator? i have tried both ways and the result is always very very similar. to do it without square rooting the denominator just makes so much more sence to me according to my definition of what average is - the sum of all the different quantities and divided by the number of quantities. squaring and square rooting in each quantity just removes the negative sign.

Thanks in advance! I cant wait to hear the reasoning behind this one!

#### recca02

Joined Apr 2, 2007
1,214
are u sure the results were same.
from what i gather abt ur problem(u arent the only one i have also been confused) isnt it like dividing by the sq root of total no of readings and in ur case by the number. so result will be different by that factor.
i think i gotta have a look how is it derived in statistics then we will be able to come to a conclusion.

#### thingmaker3

Joined May 16, 2005
5,084
just makes so much more sence to me according to my definition of what average is
Average and RMS are not the same thing.

#### mentaaal

Joined Oct 17, 2005
451
the question i am asking is why we use the quadratic mean as wikipedia calls it formula to calculate power. howcome we dont just use the arithmetic mean with all the values taken as being a positive?

the quadratic mean formula just makes no sence to me. if someone could show me how that formula is arrived at it would be great

#### bloguetronica

Joined Apr 27, 2007
1,372
RMS is related to power...but wikipedia can explain it better.