1. A rule of thumb for estimating the distance in kilometers between an observer and a lightning strike is to divide the number of seconds in the interval between the flash and the sound by 3. Show...

1. A rule of thumb for estimating the distance in kilometers between an observer and a lightning strike is to divide the number of seconds in the interval between the flash and the sound by 3. Show that this rule is correct.

2. The photo at right shows Earth science author Suzanne Lyons with her son Tristan wearing red and her daughter Simone wearing green. Below that is the negative of the photo, which shows these colors differently. What is your explanation?