Physicists poke their noses into everything, from the smallest to the largest.
The diameter of a proton is about 0.000 000 000 000 0016 m.
Proxima Centauri, the nearest star to Earth, is 40,208,000,000,000,000 m away.
Obviously, when it comes to units, one size does not fit all. This is why the SI system provides for prefixes so that units of different sizes can be formed.
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Video Explanation
Base vs Derived Units
Concept Tests
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Interesting
Why’s a Meter a Meter (SciShow)
The Kilogram has Changed. Here’s Why (Verge Science)
The Mars Climate Orbiter Incident
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