Of Particular Significance

Running Circles Around One Another

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 05/02/2024

Are you sitting or lying down? Perhaps you’re moving around at a walking pace? I probably am. And yet, unless you live in the northeastern US or in southern South America, you and I are moving relative to each other at hundreds of miles per hour.

In Chapter 2 of the book “‘Waves in an Impossible Sea”, I remarked on the this fact. (See below for the relevant passage.) At first glance it might seem puzzling. After all, the distance between your town and my town is constant; it never changes. And yet our relative motion is comparable to or faster than a jet aircraft. How can both of these things be true?

And then there’s another question: if we’re all moving so fast relative to one another, why don’t we feel the motion?

The answer to the second question: It’s the principle of relativity at work. As for the first question: Such is life on a spinning Earth.

In the book, I tried to illustrate how this works using a picture (Figure 2.) But this is one of those cases where an animation is much clearer than a static image. On this new page, I’ve presented animations that I hope will clarify the issue, in case you’re having trouble visualizing it.

Here’s the relevant quote from the book’s Chapter 2, where the principle of relativity is first discussed.

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2 Responses

  1. Hah! That’s a great point! My immediate thought was how as kids, one of would stand in the center while other rode on the rim. Both attached to the same disk, but moving very differently.

  2. Excellent commentary. I like the concept we are always in motion. My mind may have idle thoughts but my body is always ahead of me

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