Why a sidewalk has cracks every few feets

Because sidewalks are usually in places where the sun can shine

on them most of the day. Even if the sun can't shine directly on them,

the weather can get hot. Either way, the material that the sidewalk is

made of can often get hot. You know that when things heat up they

"expand" ... they actually get slightly bigger. If there were no spaces

in the sidewalk for it to get bigger, then when the material got hot and

tried to get bigger, it would crack and break, and the whole sidewalk

would be all broken up in a few months.

It is because if it was one big piece, the concrete would buckle and break just like bridges.