Mechanics

# Converting km/h to m/s

Speed ​​units are used in km/h or m/s, and the transformation between them is done using the factor 3.6.

The transformation between the units of speed kilometer per hour (km/h) and meter per second (m/s) is done using the factor 3.6. It is important to know this “transformation” because, in many exercises, the incorrect use of some unit of measurement can lead to errors. The following illustration is a schematic of how to convert km/h to m/s and vice versa:
• Why 3.6?

The conversion factor used is 3.6 due to the correspondence between the measurement units of space and time, with 1 km = 1000 m and 1 h = 3600 s. See the example of converting 72 km/h to m/s.

We see here that 72 km/h corresponds to 20 m/s, that is, a mobile that, in 1 h, moves 72 km or 20 m every second.

• everyday application

Law No. 9,503 of the Brazilian Traffic Code, in article 252, prohibits, among other things, the use of cell phones while driving. Using a cell phone can distract the driver and lead to serious accidents. Speed ​​measurement units can show this danger.

Imagine that a driver is traveling along an avenue at a constant speed of 72 km/h at the moment he receives a message on his cell phone. If that driver takes only 3 s to read the message, he will travel blind for 60 m! As we saw above, 72 km/h corresponds to 20 m/s, that is, every second, the car moves by 20 m. Thus, 3 s of eye on the cell phone makes the driver move for 60 m without seeing anything on the road, enough space for several unforeseen events to occur.

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