Session 2A: How Fast Are You Moving When You're Sitting Down?

The idea that the world is moving seemed crazy to most everyone thousands of years ago and, lets be honest, it does fly in the face of what our senses tell us. Clearly something is moving, but how can it be us? We know what it feels like when we move. And maybe you're one of those unfortunate few who get violently motion sick so you know perfectly well that you're not moving.

But you are. You're "glued" to the Earth by gravity and it's spinning around once a day. And the Earth is revolving around the Sun once every year. And the Sun is moving along through our galaxy taking about 250,000 years to travel once around. So I ask the question: How fast are you moving when you're sitting still?

Spinning in Circles

The earth is rotating on its axis, once every 24 hours we come back to the same place, facing the sun again. If we look up the size of the Earth, we can find it's diameter is about 12,750 km. But to know how far we travel (while sittting still), we need to know how far around it is. So we need the perimeter of a circle. Polygons are easy, just measure each side and add them up. How do we do it for a circle? We could just look it up, but we can also figure it out.