Word Pairs


  • Type the correct word in the boxes from the pairs of words [in brackets].
  • Click the button at the bottom to check your answers.
  • Press the "refresh" button on your browser to play again.

The words
In today's world, many things are getting [shorten / shorter] and shorter. Scientists have just measured something [incredible / incredibly] short. They recorded the shortest unit of time ever [measured / measure] . It is called a zeptosecond. This is a tiny, tiny, tiny fraction of [once / one] second. It is a trillionth of a [billionth / billion] of a second. This is a decimal point [following / followed] by 20 zeros and then a 1. The scientists study [atom / atomic] physics at the Goethe University in Germany. They used special high-tech [equipment / equipped] to measure how long it takes a photon to cross a hydrogen molecule. The scientists said it took 247 zeptoseconds for [them / this] to happen. This is too small for the human eye to see, and the time it takes is too fast for humans [to / for] sense.

In 1999, Ahmed Zewail, an Egyptian [chemistry / chemist] won the Nobel Prize in Chemistry for measuring the [speedy / speed] at which molecules change their shape. He found that one femtosecond [equally / equals] 0.000000000000001 seconds. This is a decimal point followed [at / by] 14 zeros and then a 1, or a millionth of a billionth of one second. The zeptosecond measures things in [terms / teams] of the speed of light. It is difficult for the human mind [to / so] understand these measurements. One millisecond is a thousandth of one second. This is [a / the] time for a neuron in the human brain to fire. One nanosecond is one billionth of one second. The shortest unit [of / by] time it may be [possible / possibly] to measure is one Planck. This [be / is] a decimal point followed by 44 zeros and a 1.

Back to the zeptosecond lesson.

Share this lesson

More Free Sites by Sean Banville

Online Activities