# Length

Written by Jerry Ratzlaff on . Posted in Classical Mechanics

Length (also called distance) is the dimension from one point to another point or the dimension from one end to the other end of an object.

### Length Formula

$$\large{ \Delta l = l_f - l_i }$$

$$\large{ l = \frac { 2 \; h_l \; d_p \; g } { f_d \; v^2 } }$$     (Darcy-Weisbach equation)

$$\large{ l = \frac { h_1 \;-\; h_2} { i} }$$     (hydraulic gradient)

$$\large{ l = \frac{ \lambda }{ Kn } }$$     (Knudsen number)

$$\large{ l = k_t \; \frac{\Delta T}{\dot {Q}_t} }$$     (linear thermal expansion coefficient)

$$\large{ l = \frac {M}{F} }$$     (moment)

$$\large{ l_s = \sqrt{ \frac{ 2 \; PE_s }{ k_s } } }$$     (spring potential energy)

$$\large{ \Delta l = \epsilon \; l_i }$$     (strain)

Where:

$$\large{ l }$$ = length

$$\large{ f_d }$$ = Darcy friction factor

$$\large{ F }$$ = force

$$\large{ g }$$ = gravitational acceleration

$$\large{ h_l }$$ = head loss

$$\large{ \dot {Q}_t }$$ = heat transfer rate

$$\large{ i }$$ = hydraulic gradient

$$\large{ Kn }$$ = Knudsen number

$$\large{ \Delta l }$$ = length differential

$$\large{ l_f }$$ = final length

$$\large{ l_i }$$ = initial length

$$\large{ v }$$ = mean flow velocity

$$\large{ \lambda }$$ (Greek symbol lambda) = mean free path

$$\large{ M }$$ = moment

$$\large{ d_p }$$ = pipe diameter (ID)

$$\large{ h_1 }$$ = pressure head at point 1

$$\large{ h_2 }$$ = pressure head at point 2

$$\large{ k_s }$$ = spring force constant

$$\large{ PE_s }$$ = spring potential energy

$$\large{ \epsilon }$$  (Greek symbol epsilon) = strain

$$\large{ \Delta T }$$ = temperature differential

$$\large{ k_t }$$ = thermal conductivity constant