Editing Dynamometer car (section)

== Power calculations ==
The operating principle of the dynamometer car is based on the basic equation for [[Horsepower|power]] being equal to force times distance over time.
:<math>P = \frac{F\cdot d}{t}</math>
This equation can be reduced to power equals force times velocity:
:<math>P = F\cdot\frac{d}{t}=F\cdot V</math>
In other words, the instantaneous power output of the locomotive can be calculated by measuring the pull on the coupler and multiplying by the current speed.

:<math>P =50,000 ~ \text{lbf} \cdot \frac{30 ~ \text{mi}} {\text{h}} \cdot \frac{5280 ~ \text{ft}}{\text{mi}} \cdot \frac{\text{h}}{3600 ~ \text{s}} = 2,200,000 ~ \frac{\text{ft} \cdot \text{lbf}}{\text{s}}</math>

Converting to horse power gives:

:<math>P = 2,200,000 ~ \frac{\text{ft} \cdot \text{lbf}} {\text{s}} \cdot \frac{1 ~ \text{hp}}{550 ~ \text{ft} \cdot \text{lbf} / \text{s}} = 4,000 ~ \text{hp}</math>