The first activity in each unit is usually an exploration, like this one.

It's About Time!

1. Please familiarize yourself with the stopwatch in the kit. The only thing we want it to do is start counting from zero and then stop, when we tell it to do these things. Some stopwatches have many other capabilities, which can be confusing if the watch is in a mode other than the timing function.
2. Practice timing something. For example, try to verify that it takes 10 seconds for the second hand on a clock to get from 12 to 2 (watch the other clock, not the stopwatch!).
3. You will not be able to start and stop the watch exactly on time, and so the 10 second event probably will not give a stopwatch reading of 10.00, except by accident (it can happen once but not repeatedly). If your measurements are always between 9.95 sec and 10.05 sec (when the actual event is 10 seconds), we will say that the accuracy is 0.05 sec. How accurately can you do this?
4. Try timing 5 seconds by having a partner tell you when to start and stop. How accurate are you at doing this?
5. Compare what happens when the partner says "ready ... set ... go" and "now .. we ... stop" so that you can anticipate when to start and stop.
6. One way to improve your accuracy is to make the measurement several times and then calculate a "central measure." One common central measure is the average. A less familiar one is the median, which is a number such that half of the measurements are larger and half are smaller. The average and the median can be determined accurately from inaccurate measurements, because many measurements contribute.

   The average and the median are usually close to each other. The median of a list of numbers is easy to find: you cross off the largest value and the smallest value, and then the largest and the smallest of the remaining values, and so on until you have only one left (if there is an even number of values, take a value between the last two to survive).

   As an example, make 5 attempts to time the second hand for a 10 second interval, and then calculate the median and the average.

Check the box when you are done: