It’s not the easiest thing
to describe human motion.
Here’s a class exercise to discover
the big picture.
For that, however, you need to use the DOOR.
Where are we in the universe? And what are we doing?
First, examine some real motion we rarely think about. Though we may be sitting very still and think nothing is happening, if we could look at ourselves from very far away, we are continually m o v i n g — very, very fast, in circles, or almost circles. The vehicle is our spherical planet that isn’t stationary at all. Rather it’s rotating on its axis continually, revolving around the sun, which is one of billions of stars in a disk-shaped group called the Milky Way that itself is moving in a curved path that we believe is part of an even larger circle.
The best way to illustrate this is with a class of 20 to 40 or so 6th grade students on the corner of a football field that we’ll call rectangle ABCD where (on a sheet of paper standing up) AB and CD are the “long” 100 yd. parts and AC and BD represent the 53.3 yd. widths at each end. Form a circle of students at the “upper” left corner so that the circle itself just comes as close as it can to “A” (touching the sideline and goal line there). You stand in the center of this circle as best you can, and begin with every student—at first—facing you. Each student (depending upon size of the group) should be about 10 feet—or the same distance—away from you. Next you give them the ground rules:
“(1) I am the sun, and each of you represents Earth at a particular time during a year. (2) Imagine yourself holding a smart phone in your hands, and sitting in an office chair that can easily spin around and around. Your world is the game you are playing over and over on your phone. (3) You have three jobs: First, I expect your circle of people to slowly and continually walk counterclockwise in a circle; and second, to constantly turn around, as if still on your rotating chair, at a constant speed to represent the rotating of Earth on its axis as you do this. Glance around at everyone else doing the same thing to try and stay at about the same speed. You don’t have to be exactly the same, however. Third, I, representing the sun, will be moving as well, so keep me in the center of your circle.
“(4) I will work my way to the other end of the football field, representing the way the sun moves through space. That’s my problem to do right! We should, by the way, end up in the same circle tight in the corner at “B” where our circle-moving will end. As to what I, the sun, will do is this: I will make a semicircle coming as close as I can to the 50 yardline (between C and D) without pushing any of you off the field.”
“With a warm day and a light breeze and your brains staying in place, you will do well in the game you’re playing on your phone and will enjoy yourself.”
Your understandings from this modeling exercise (speaking now the reader) are these:
Your body, as a whole, is always in motion in ways you can’t sense.
You (and your planet) are always moving in “curves.”
This motion is a complex series of curves.
Though this motion is real, and measurable by science, it’s sometimes a bit hard to follow and understand. But with a little persistence, you can figure things out.
Things work out a little better using straight lines (and letting curves take care of themselves)¹
¹ There, we got our footnote in! We’ll have a lesson on straight lines, and how to think using them, later on.