- What keeps the Earth orbiting the Sun instead of shooting off into space?
- How do figure skaters achieve such elegant spins?
As I mentioned earlier, we spend most of our time on a giant hunk of rock that is moving in a circle (approximately) around the sun, just like every other planet in the solar system. And the sun is circling the center of the galaxy. In fact, if you spend enough time looking out into space, you start to realize that almost everything out there is either spinning around, orbiting something else, or both. And understanding that motion represents an important step in the understanding of physics as a whole.
What makes an object move in a circle? Perhaps a more useful question to ask first is, why don’t objects usually move in circles? We know from Newton’s First and Second Laws that objects keep moving in a straight line (or stay stationary) unless an external force causes them to speed up, slow down, or change their direction of motion. And yes, if you’ve been reading carefully, you’ll notice that this answer amounts to a fancy way of saying, “Because.” A slightly better answer might be, “Because space seems to be aligned in straight lines rather than curved ones,” but the truth is, that answer is just yet another way of restating the question.