When does an elastic metal rod change its length?

An elastic metal rod will change its length when it a) falls vertically under its weight b) is pulled along its length by a force acting at one end c) rotates about an axis at one end d) slides on a rough surface

Identify the case when an elastic metal rod does not undergo elongation

Identify the case when an elastic metal rod does not undergo elongation

How does eye lens change its focal length ?