what does "linear" mean?
I've looked it up in dictionary. It has some meanings: of length or lines, going from one thing to another in a single series of stages. But in this case: "It’s not a linear relationship. Eighty decibels is twice as loud as 70 decibels, and 90 decibels is four times louder". What does it mean? I apply aforementioned meanings but it doesn't seem to match.

Answers · 6

What is your background?
I'll assume some maths.
I can try without maths if you need it.
dB is a log scale.
The markings on a ruler are "linear". Each 1cm you move along a ruler means the distance is greater by the same amount.
2cm is twice as far as 1cm
3 cm is twice as far as 1cm
x cm is x times as far as 1cm.
d = xcm This is a linear relationship.
not quadratic, d = x^2, not cubic, d = x^3.
d = xcm is a linear equation.
Bels, as in deci-Bels is a log scale. Distances along the dB scale are log(quantity)
As they explain each Bel, 10 dBels makes it times 2 loudness. 1 2 4 8 , not linear 1 2 3 4
Earthquakes are also ranked on a log scale. a 7 is much bigger than a 6. (Again, not a linear scale)
Hope this helps.
Comment if you need it explained differently.
The linear meaning you found is to do with sequences of things, not multiple paths. It's different.

This is the definition you should be using:
Mathematics--able to be represented by a straight line on a graph; involving or exhibiting directly proportional change in two related quantities
If they had a linear relationship, 140 decibels would be twice as loud as 70 decibels--this is not the case here.

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