Question

What is the physical significance of inertia?

Answer 1

Inertia is the property of matter by which it retains its state of rest or its velocity along a straight line so long as it is not acted upon by an external force. Inertia is necessary to maintain certain other forces such as constant velocity. For example, an orbiting body without its own propulsion depends on inertia to maintain its constant velocity which counters gravity. The rockets would run out of their fuel in a very short time. The inertia they build during ascent is what keeps them in orbit.