It is a riddle.
It is the strongest force,
to resist your force,
and yet it is not a force.
It never accelerates,
but it is always moving.
It never rests, and
it never gets tired.
It has been defined many ways,
but no one can quite capture it.
What is it?
There is no fixed solution of this kind of question. It is up to our wild imagination.
The question might refer to gravity.
Gravity is the strong force since it manages all the planets in this universe so as not to cause them to clash with each other at anytime.
Gravity could resist the force of upward movement. For instance, you throw an object up to the sky. The object could fly upward freely if there is no influence of gravity. With the gravity, the object would force to drop immediately.
Nobody could feel the gravity. To them, it is not to be considered as a force.
Gravity can never accelerate and it always maintains at the same.
Gravity is always moving since it causes all the planets to maintain the same place of their movement every day.
Gravity never rests since it always exists in this universe.
Gravity can never get tired since it is not human being.
Gravity has been defined many ways since it is applicable everywhere in the society especially the Newton principle.
No one can quite capture it since nobody knows how there could be gravity in the universe.
There could be other alternative solutions and it depends upon our imagination and how we link other objects up into the question.