8 September 19

Stomp your feet today for gravity! Today's date can be written 9-8, which makes it Gravity Day on some calendars -- because the gravitational acceleration near the Earth's surface is 9.8 m/s². The newest tie in my collection (a birthday present from Mom Wollenweber) features many of Isaac Newton's equations of motion and gravitation. Albert Einstein completely changed our understanding of how gravity works, but Newton's equations are still very useful, even guiding all of the calculations for aviation and lunar and interplanetary exploration.