The real reason why escalator stairs have grooves

[ahlam1399]

http://img-s-msn-com.akamaized.net/tenant/amp/entityid/AAv8OZL.img?h=100&w=100&m=6&q=60&o=f&l=f&x=548&y=207If youâ??re one of the millions of Americans who use escalators each year, you are probably deeply familiar with the vertical grooves that cover each stair.

أكثر... (http://www.msn.com/en-ca/lifestyle/whats-hot/the-real-reason-why-escalator-stairs-have-grooves/ar-AAvaRH4?srcref=rss)