Instantaneous or average? Ask when it belongs

What is an instantaneous velocity?

You've already seen the two kinds of velocity: an instantaneous velocity belongs to one moment; an average velocity smooths an interval. Real sentences rarely announce which they are. You classify them from the wording.

Ask one question of the statement: WHEN does the velocity belong, to a single moment or to a stretch of time? A single moment gives an instantaneous velocity; a stretch gives an average velocity.

'The car was doing 30 m/s east as it passed the sign' pins one moment: instantaneous. 'The car made 30 m/s east across the whole drive' spans a stretch: average. Same car, same value; only the WHEN changed.

Statement 1: 'The car averaged 9 m/s toward the depot over its full run.' Statement 2: 'The car was moving at 11 m/s toward the depot as it passed the clock tower.' Classify each velocity as instantaneous or average.

'The cyclist was moving at 12 m/s toward the arch the instant the bell rang.' Ask when the velocity belongs: 'the instant the bell rang' pins a single moment. The statement gives an instantaneous velocity.

Four race reports mention a velocity. Which report states an AVERAGE velocity?

'Across the whole crossing, the boat made 5 m/s toward the island.' 'Across the whole crossing' stretches over an interval. The statement gives an average velocity.

The size of the value and the length of the journey play no part. Only the WHEN decides.

Statement 1: 'The gondola was moving at 3 m/s up the cable at the exact moment it cleared the first tower.' Statement 2: 'The gondola managed 2 m/s up the cable between the two towers.' Classify each velocity as instantaneous or average.

Your turn

A crash investigator's file contains four velocity entries about the same car. Which entry is an INSTANTANEOUS velocity?

Statement 1: 'Leaving the dock, the boat was making 1 m/s downstream.' Statement 2: 'The boat covered the river's straight section at 2 m/s downstream overall.' Classify each velocity as instantaneous or average.

A drone's flight log holds two entries: (1) '5 m/s due west, logged the instant the camera fired'; (2) '4 m/s due west for the outbound leg'. A student calls BOTH entries instantaneous 'because each names one specific flight event'. What is wrong with the student's reasoning?