TASK DEFINITION: Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.
PROBLEM: Sentence1: Nonmetal elements are far fewer in number. 
Sentence2: There are 17 nonmetals on the periodic table.

SOLUTION: Nonmetal

PROBLEM: Sentence1: when a gas in an open container evaporates , that gas spreads out into the air. 
Sentence2: when a gas in an open container evaporates gas molecules slamming into one another.

SOLUTION: container

PROBLEM: Sentence1: gravity causes objects that have mass to be pulled down on a planet. 
Sentence2: And roller coasters work with gravity.

SOLUTION:
gravity