Is a robot arm input or output?

The thermal expansion or contraction of a given metal is a function of the f a)-density b)-initial temperature c)- temperature difference d)- linear coefficient of thermal expansion e)- final temperature f)- original length

What is the heat treatment of metals? what is the benefit of it? why and how it's useful? answer in details, do not write by hand.

Modern high speed trains do not have perpendicular expansion gaps where rails are joined end-to-end any more they are mostly welded together but what might happen if there was a spell of particularly hot weather that causes inspection of the tracks?