Calculating Speed – a Boggling Endeavor
Unbridled discussions on speed, how to calculate it and what the results of the calculations actually mean, are deep, intriguing and ultimately somewhat mind boggling. The basic formula for calculating speed is simple: distance divided by time. But what does the answer to that calculation actually tell us?
Here, I’ll show you what I mean. You are riding on a train. The train is traveling east at 60 mp/h. You stand up and start running east at a speed that you know (from countless hours on a treadmill) to be 3 mp/h. What is your speed? Now, suppose you turn around and run west. What is your speed? When you are running east, is your speed 3 mp/h or 63 mp/h? And when you run west, is your speed 3 mp/h or 57 mp/h? But wait, we’ve only just begun.
Remember the train you started running on? Well, if it was located at the equator, then even if it is parked at the station, it is traveling at the speed of the earth’s rotational spin, which is over a 1,000 mp/h in the equatorial regions. Conversely, if the train was at one of the poles, the earth’s rotational spin speed would be only a fraction of that. It’s like a merry-go-round: the spindle turns at a steady rate, but the rotational speed on the outer edge of the carousel is much greater than at its center.
Next comes the speed of earth as it orbits the sun. The average orbital speed of earth is well over 66,000 mp/h. So then, if you are standing on the equator, you are traveling at a speed well in excess of 67,000 mp/h. Think that’s fast – just wait.
Now we get to add in the speed at which the sun, with the earth in tow, orbits the center of the Milky Way Galaxy. There are different methods used to compute this speed, I’ll just pick one at random. The sun orbits the center of the Milky Way Galaxy at around 1,409,040 mp/h. I wonder why my hair isn’t blowing around…
Of course we could go on to the speed at which the Milky Way Galaxy scurries through the universe, but since we’re already traveling at around 1.5 million mp/h – I better stop and move on to other perplexing matters of speed.
Does one determine the speed of a rocket ship by using its point of origin in the calculation, or its intended destination? When a rocket is launched from earth in the same direction which the earth travels around the sun, it won’t pull away nearly as fast as when it’s launched in the opposite direction. The same principle holds true for its destination.
From the above, it’s easy to see why Einstein knew we absolutely needed a standard for speed. According to Einstein, light sets the bar for speed in our universe. And his theories have held up well under almost a century of intense scientific scrutiny. In the beginning of his work, The Theory of Special Relativity, Einstein establishes a cosmic speed limit: nothing can travel as fast as light: 186,000 mp/s. Now we’re getting somewhere! But then later comes the troubling matter of time dilation.
Time dilation refers to the phenomenon: the closer you get to traveling at the speed of light, the slower time passes – for the traveler, that is. Everyone else is stuck in ‘real time.’ What this boils down to, by way of example, is simply this: if you board a spaceship that is capable of achieving .9 the speed of light, and depart earth headed for the center of the Milky Way Galaxy – you’ll arrive in what you perceive to be about 20 years or so. But to the folks back on planet earth, almost 30,000 years will pass during your trip. So would you calculate .9 light speed using the tempo of time on the spaceship, or using an earthbound tempo?
Discussions on time dilation usher in the debate over the possibility of time travel. If one manages to defy physics and travel at speeds greater than light speed, will one go back in time? But that’s another story.
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