The phrase “120 kilometres an hour” (often written “120 km/h”) is a colloquial expression denoting a speed of one hundred and twenty kilometres travelled in one hour. It is not itself a distinct encyclopedic entry; rather, it is an instance of the standard unit of speed, the kilometre per hour (km/h), which is defined as the distance of one kilometre covered in the time span of one hour.
Unit definition
- Kilometre per hour (km/h): The International System of Units (SI) recognizes the metre per second (m·s⁻¹) as the base unit of speed. The kilometre per hour is a derived unit, related by the conversion 1 km/h = 0.277777… m·s⁻¹.
- Conversion: 120 km/h is equivalent to 33.33 m·s⁻¹, or roughly 74.56 mph (miles per hour).
Typical usage
- The expression is commonly employed in road traffic contexts to describe vehicle speed limits, typical cruising speeds of automobiles, and performance specifications of motor vehicles.
- In many jurisdictions, speed limits are posted in kilometres per hour, and “120 km/h” often represents the maximum permissible speed on certain highways or freeways.
Etymology and linguistic notes
- “Kilometre” derives from the French kilomètre, itself a combination of the Greek prefix kilo‑ (meaning “thousand”) and the metric base unit “metre”.
- The preposition “per” is frequently omitted in everyday speech, rendering “kilometres an hour” as a syntactic variant that conveys the same meaning as “kilometres per hour”.
Contextual considerations
- While the phrase accurately conveys a quantitative speed, it does not denote a separate concept beyond the underlying unit of measurement. Consequently, there is no dedicated encyclopedic article for the specific phrase “120 kilometres an hour”.