rarefaction

"The high population density of the city meant there were many people living in a small space. "

"To separate out the chaff, early cultures tossed baskets of grain into the air and let the wind blow away the lighter chaff."

"The sudden announcement of a school holiday surprised everyone. "

"My sister is very helpful, especially when it comes to organizing things. "

"Asphalt, composed of oil and sand, is a widely used material for roads."

"The water in the swimming pool is a fluid that easily takes the shape of the pool. "

"The miners used dynamite to shatter rocks."

"The reduction in homework assignments allowed students more free time. "

"He stopped at a nearby store for some groceries."

"The lightning caused thunder."

"The firework display ended with a spectacular explosion of color and sound. "

"Apply pressure to the wound to stop the bleeding."