Question

Does A Speedometer Of A Car Measure s It's Velocity​

Answer 1

Time to get really nitpicky! First I’ll assume this is the type of speedometer that does not put out a reading when you’re going backwards. Technically all it measures is the rotational velocity of the tires. If you spin the tires on ice for example, you go nowhere but it still might show 40mph. If we want to get even more nitpicky we might say it only directly measures the rotational velocity of the actual gear ring the sending unit is attached to, and then extrapolates that to the differential since one tire might slip and the other might have traction. (In a diff, the sum of the two rotational velocities is added together to equal the output, including when one or both values is a negative number. A differential can be used as a purely mechanical adding machine, and was in WWII bomb sights! Cool stuff!) Then it extrapolates that to the tires, and multiplies that by pi and by tire diameter, and calibrates it all together to match up with a gauge face printed to display 0-140mph ground speed across a 270-degree sweep.

So velocity, because rotational velocity of the sending unit gear, whose direction is known and is always constant for any forward vehicle motion greater than 0. Doesn’t matter if the car’s going north fast, west slowly, around a corner, or whatever.