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Question
How can Newton's first law of motion be obtained from the second law of motion?
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Solution
From Newton's second law of motion, F = ma.
If F = 0, then a = 0.
This means that if no force is applied on the body, its acceleration will be zero. If the body is at rest, then it will remain in the state of rest and if it is moving, then it will remain moving in the same direction with the same speed. Thus, a body not acted upon by an external force, does not change its state of rest or motion. This is the statement of Newton's first law of motion.
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