SEE A RAINDROP
Fill the shoebox lid with flour.
Use the ruler to smooth out the top, so that its level.
When it rains, hold the shoebox lid out in the rain until about 15-25 raindrops have fallen into the flour. Bring the lid inside to see what you've found.
Set the sieve over the bowl. Carefully pour the flour from the lid into the bowl. Shake the sieve gently.
The little lumps left behind are preserved raindrops. Carefully dump them out onto a table and measure them!
Most raindrops are relatively small because big ones usually break apart as they fall. The world's biggest raindrop fell near Hilo, Hawaii. It only measured 8mm or 1/3 inches across. To give you an idea of how big that is, its smaller than your baby fingernail.