What is mightier than steel yet cowers from the sun?

Ice is mightier than steel yet cowers from the sun.

Explanation

Steel is the hardest metal used in building heavy vessels for sailing or other kind of transportation.

But as it is a metal, it has freezing point so the steel may get frozen leading to failure in the working of ships at low temperatures.

Even vessels like ships, submarines can break if collided with ice blocks in the northern pole region.

So ice has the capacity to weaken the steel but it will melt easily in sunlight.

So ice is the one which mightier than steel yet cowers from the sun.

the correct answer is "inertia"