Speed

SPEED

A TRIP TO PORTLAND

Late last November, I traveled to the nearby city of Portland, Oregon, which is a drive of about one hundred miles from my home in Corvallis. Departing at 1:30pm, I arrived in Portland at 3:30pm. My appointment that day was pretty important to me, so I was glad that I was able to arrive on time.

RADAR
There was some excitement during the drive. In fact, I was very fortunate not to receive a speeding ticket as soon as I left home. After pulling out onto Grant Street, a residential street that runs by my house and where the speed limit is 25 miles per hour, I accelerated rather too quickly. Only then did I notice the police car parked in a side street, radar at the ready! A panicked glance at my speedometer revealed that I was going much too fast. The officer pulled me over and indicated that she had clocked me on radar at a speed of 38 miles per hour.

... got caught Actually, that's about all there is for this story. The officer let me off with a stern warning. And despite the delay, I was able to reach Portland on time, so my story has a happy ending.

THE END

This story involves at least two different measurements of speed:
average speed and instantaneous speed.

The following questions are designed to help us understand the distinction between these measurements.

Question 1. How did I know when to leave home? [Time?]

Question 2. How did the officer know that I was traveling at a speed of 38 miles per hour? [38?]

These questions have some obvious answers that only lead to more questions. One could answer Question 2 by saying: "She looked at her radar detector." True. But then ask yourself: How did the radar detector know that I was traveling 38 miles per hour?

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Question 1.	How did I know when to leave home?	[Time?]
Question 2.	How did the officer know that I was traveling at a speed of 38 miles per hour?	[38?]