Question

What does the odometer of an automobile measure?

Answer 1

Hint: In Greek, the meaning of the word odo means path, and you know what meter means (measuring device). A Speedometer is a device that measures speed, voltmeter is a device that measures voltage.

Complete step-by-step answer:
Odometer is a device which measures the distance covered by an automobile. The word itself is composed of two Greek words odo and meter, where odo means path and meter is used for an instrument that measures. Sometimes it is also called odograph.
Odometers can be of two types: Mechanical Odometer or Digital Odometer.
Odometers work in principle of interconnected wheels. As the car moves its wheels rotate, and each complete rotation of the wheel the car travels a distance equal to the circumference of the wheel. That is:
 $\begin{align}
  & \text{Circumference}=2\pi R \\
 & \text{Distance}=2\pi R \\
\end{align}$
R being the radius of the tire.
Now all the odometer does is count the number of times the tire completes its rotations. Let’s say the count is N number of times, then the total distance travelled is $N\times 2\pi R$.
The digital odometer uses a magnet that is fixed on the rotating wheel and as it rotates it produces an EMF in a small current loop that is fixed on the car. This circuit is designed to count the number of times current flows in the loop.

NOTE: Odometer can work on any moving vehicle which has wheels. From ancient times kings have been using similar devices like in Imperial China Han Dynasty, Song Dynasty and later many more. The first odometer was proposed by Vitruvius around 25 BC.