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Bigger or Smaller?

When you change the units, do the numbers get bigger or smaller?

Choose Your Units

Age 14 to 16 Challenge Level:


Some units are particularly well suited to a given measurement because they turn out to give a small, whole number of units. Understanding this concept gives you a feel for the order of magnitude of the quantities.

What units would you measure these quantities in to make an approximation which was a reasonably small whole number?

  • The volume of a bacterium
  • The mass of an oak tree
  • The area of a leaf
  • The half-life of Uranium-235
  • The area of a football pitch
  • The average lifespan of a human
  • The volume of a bath tub
Can you reverse the process? For the following units, what physical phenomena might naturally be measured to be around 1 unit?

  • Millimetre
  • Newton
  • Angstrom
  • Joule
  • Volt
  • Microgram
  • Micrometre
  • Hertz
  • Parsec

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