about 1st n 2nd laws of dynamic(Newton's!)?

Question

in 2nd law of dynamic(Newton's) we have: F=ma so if F=0 ---> then a=0 ---> V= cte
which is the 1st law, right? ( if F=0 then V = cte )
why did Newton separate these 2? doesn't the second law include the first one?

so what i said (if f=0 then ...!) includes the 1st law not the second law?

Answer 1

Not only first and second, but all three laws are interrelated by concept of inertia.
Paraphrasing three laws
1.If the sum of the forces on the object is zero if will be at rest or move with a constant speed. (The inertia of the object keeps the object moving with a constant speed)
2.If the sum of the forces on the object is NOT zero the object will move with acceleration in the direction of the force. (The inertia of the object resists the force applied. To maintain acceleration as in F=ma the force must be continuously applied)
3.If a force applied to the object the object applies an equal force back. (The inertia of the object resists and fights back)

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Answer 2

No. First law is very important and is not included in second law. First law states the principle of inertia. What is at rest will remain at rest and (more importantly) what is in motion will continue in motion unless acted upon by an external force. Second law define acceleration and force. First law is about state of rest or UNIFORM motion. The second law is about change in state of rest or change in the state of uniform motion. These are distinct and hence need to be separated.