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Opens on Chapter 21’s example: walking 25,000 miles at 3 mph.
Walk around
Light time
Weight of the air
A pool in bathtubs
Everyone standing together
Enter your numbers, then press Calculate.
From the book, Chapter 21. 25,000 miles at 3 mph is 8,333 hours: 347 days nonstop, or 2.9 years at 8 hours a day. Light crosses the 384,400 km to the Moon (NASA) in 1.28 seconds, 2.6 there and back. 14.7 pounds on every square inch of 197 million square miles is about 5.3 × 10¹⁸ kg; NASA gives the atmosphere’s mass as about 5.1 × 10¹⁸ kg. An Olympic pool (50 × 25 × 2 m, at least) is about 8,333 baths of 300 liters. 8 billion people at 2.5 square feet each fill about 717 square miles.
Rounding is half up, the way the book rounds. Numbers can be typed as 1,450, $38, 12%, 1/20, 2.5 million or 3 × 10⁷. Everything stays in your browser: no sign-up, nothing stored or sent.