: How is the Horsepower of a car measured? And how did they measure it for the firsts motored cars?

Question

: How is the Horsepower of a car measured? And how did they measure it for the firsts motored cars?

In: Engineering

Answer 1

We measure rotational power output with dynamometers. They vary in form but the general idea is to accelerate a mass with known characteristics over a set length of time.

For example, if we have a tire in contact with a steel drum (and we know the drum’s rotational inertia – it’s resistance to accelerating) we can measure the change in spinning speed of the drum over a period of time. Since w can calculate how much energy it takes to speed up the drum that much and since we measured the time, we can calculate power (energy/time)! The math for ths method had been around longer than motor vehicles.

Other dynamometers test engine (or shaft power) by accelerating a fluid (like water or oil) with a pump.