Now that you are suitably forewarned, the aspect I of physics I want to talk about is reference frames and motion. It is quite unintuitive to us in our everyday lives that everything is always in motion. Most of us are aware of this fact to some extent but the really interesting thing is the full extent to which things are in motion. Consider two travelers. One is standing on a platform at a train station and the other is on a train that is trundling by. We mostly understand the relative motion of these travelers by assuming that the one on the platform is stationary and the one on the train is not. (As demonstrated by Frank and Joe below) This is a perfectly reasonable assumption for everyday life and even a fair assumption as a defined reference frame.
|I spent whole ones of seconds on this beautiful diagram - All rights reserved!|
The most obvious motion that we all undergo without noticing it is the motion of the earth itself. It is rotating. It is rotating quite fast. Standing on the surface of the earth you are moving at about 1000 miles per hour at the equator but you are barely moving at all if you are standing at either of the poles. Quite a difference but you wouldn’t feel it in either place. If you throw a ball straight up in the air, it will appear to go up and down in a straight line. This is because, relative to the rotating earth, you and the ball are rotating with the earth at roughly the same speed. The interesting thing is that, if you could throw the ball high enough, it would seem to curve away from you. You would, in fact, be rotating away from the ball on the surface of the earth. If you are facing the direction of rotation, the ball would land behind you. The higher you throw it, the further behind you it will land. The other obvious motion of the earth is its movement around the sun. The earth is moving at something like 67,000 miles an hour around the Sun. This is where most of us stop expanding the reference frames and we mostly think of the Sun as static. The interesting thing to me, is in realising that the Sun itself, and it’s planetary system are hurtling through space at something like 400, 000 miles per hour (using the distance of the solar system from the galactic core (approx 25,000 - 28,000 light years) and the period of rotation (approx 225-250 million years). 400K mph is pretty fast.
Just how relative movement is, becomes more obvious when we lack a “static” reference. Up until now, the relative motions are calculated in reference to something that can be considered static. Like the sun for calculating the motion of the earth around it, or the galactic core for considering the motion of the entire Solar system. When we get to the scale of galaxies, the whole exercise becomes a little trickier. How fast is the Milky Way itself moving through space? Well that depends. It depends on what other object in space you gauging its motion relative to(Cosmic background radiation, other galaxies?). No matter what reference frame you choose, the speed will be high; something on the order of several hundred thousand mph to a few million mph. Consider also that you are moving in all these ways simultaneously right now. It’s almost enough to make you fell dizzy. Is it also possible that the universe itself is moving, though I am not sure through what, and this motion would be relative to other universes? In short, motion is always relative and everything is always in motion. Without other things for motion to be relative to, “motion” doesn’t really make sense at all.