Wonderfest contributed to authorship of this lesson. Wonderfest's Mission is to inspire and nurture a deep sense of wonder about the world. We aspire to stimulate curiosity, promote careful reasoning, challenge unexamined beliefs, and encourage life-long learning. We achieve these ends through public science gatherings in the San Francisco Bay Area and through online science discourse & video that reach around the world.
For a good introduction to the meaning, calculation, and relativity of speed, watch this episode of Radical Physics: http://youtu.be/MIRyWA0VoeM.
Speed is relative, but change in speed is absolute. To better understand why, watch this episode of Radical Physics on the meaning of force: http://youtu.be/wcmB1JtGqa4. It is the (net) force on an object that causes its speed to change.
This TED-Ed video states that space is nothing—that it is “no thing.” However, some “things” do permeate virtually all of space throughout the universe. These things don’t serve as a universal standard of rest, but they are still interesting and important. Here are short videos that introduce each such “inhabitant” of space. Not only are these inhabitants very different from each other, but the styles of these three videos are very different—different from each other AND from TED-ED and Radical Physics videos.
• The interstellar medium: http://www.youtube.com/watch?v=DUkBmURrZjo. This two-minute Ask An Astronomer video is quite elementary, but does the job.
• The cosmic microwave background radiation: http://www.youtube.com/watch?v=_mZQ-5-KYHw. This Minute Physics video is remarkably insightful, but may try to do too much too quickly in its 4 minutes.
• The quantum vacuum: http://www.youtube.com/watch?v=J3xLuZNKhlY. This 5- minute Veritasium video is provocatively entitled Empty Space Is Not Empty.
The best reply to the question “How fast are you moving?” is “Relative to what?” However, most every physics text has a table of “fundamental constants" that includes the speed of light, “c = 299,792 km/s,” … without reference to any standard of rest. How can that be? In that same table of constants we may find fundamental masses, distances, electric charges, etc., but we sure shouldn’t find any speeds! How can the speed of ANYTHING be a fundamental constant when we’ve learned that all speeds are relative?!
Have you ever thought about writing about someone slowing down? I guess you could write, "And then, he pressed the brakes and the car accident was over very quickly." But what if you wanted your readers to experience the moment the action took place? Check out this lesson to hear more.

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