Answer to Question #230652 in Classical Mechanics for Moontaha

Question

during a lesson on Newton's Law of Motion, student says 'we don't really need to bother with Newton's first law because it is included in his second law '

state Newton's first law of motion and explain how Newton's second law includes the first law

Answer 1

'we don't really need to bother with Newton's first law because it is included in his second law' - This statement is not correct.

Newton's first law:

There are such frames of reference, called inertial, relative to which material points, when no forces act on them (or forces are mutually balanced), are at rest or in uniform rectilinear motion.

Newton's second law:

In the inertial frame of reference, the acceleration that a material point with constant mass receives is directly proportional to the resultant of all forces applied to it and inversely proportional to its mass.

$\vec F = m\vec a$

The special case $\vec F =0$ for of the second law cannot be considered as equivalent to the first, since the first law postulates the existence of inertial frames of reference, and the second is formulated already in inertial reference frames.

Answer: the student's statement is not correct