spadnie

In a sentence

• Jeśli będzie mroźno, temperatura spadnie poniżej zera.

  If it gets frosty, the temperature will drop below zero.

  Here, 'spadnie' is used to describe the decreasing of a measurable value, specifically temperature.

• Gdy wiatr się nasili, liście spadną z drzew.

  When the wind picks up, the leaves will fall from the trees.

  In this sentence, 'spadnie' (here in plural 'spadną') refers to objects, leaves, moving downward due to gravity.

• Mam nadzieję, że nie spadnie żadna gałąź podczas burzy.

  I hope no branch falls during the storm.

  Here, 'spadnie' expresses the possibility of downward motion of an object, specifically a branch.