Distance travelled and time taken. Units of distance and time
The length of the trajectory a body has covered is the distance, denoted s. The SI unit of distance is the metre (m); long distances are measured in kilometres (km): 1 km = 1000 m, 1 m = 100 cm. The duration of motion is time, denoted t, with the unit second (s). For longer intervals we use the minute and hour: 1 minute = 60 s, 1 hour = 60 minutes = 3600 s. Before calculating, bring all quantities to the same units. For example, 2 hours = 2 · 3600 = 7200 s, 3 km = 3000 m. Distance and time are measured with an odometer, a tape measure, a stopwatch and a clock.
“Measuring by steps”: a pupil counts steps from the desk to the door, measures one step with a tape measure, calculates the distance and records the time with a stopwatch. Safety: walk slowly and do not run.