13. Brain waves are even more active while you are dreaming. When you are fast asleep, you might think that your brain is "shut off", but it is actually doing a whole lot more than when you are walking, talking, eating, and thinking. When awake, people demonstrate mostly alpha and beta activity. Sleep uses theta and delta activity which are greater in amplitude than alpha and beta.
14. Light (299,792,458 m/s) travels faster than sound (340 m/s). So during a thunderstorm you will see the lightning before hearing the thunder. If you are close to the lightning, the thunder will boom right after the lightning, but if you are far away from the lightning, you can count several seconds before you hear the thunder. The further you are from the storm, the longer it will take between the lightning and the thunder. How long? How far? After you see a flash of lightning, count the number of seconds until you hear the thunder. For every 5 seconds the storm is 1.6 km away.
15. When traveling through water, sound moves around four times faster than when it travels through air. A whale’s song can travel up to 10,000 miles through the ocean!
16. A plain chest x-ray exposes a person to the equivalent of 10 days of naturally occurring background radiation. A CT scan of the chest is equivalent to two years of radiation.