why Newton's second law of motion considered as real law of motion? Explain.
Answers
We shall now state that Newton's 1st law and the 3rd law is contained in 2nd law
According to Newton's second law :F=ma
If F=0 then a=0,m is unequal to 0
Which states that there will be no acceleration in the body if no external force is applied on it.This means that a body in rest will remain at rest and a body in uniform motion will remain in uniform motion which is also stated in Newton's 1st law.
Now,let F1 is the force exerted by a body A on B and F2 is the force exerted by body B on A .
Change in linear momentum of body A= F1×∆t
Change in linear momentum of body B=F2×∆t
Then,F1×∆t+F2×∆t=0
F1×∆t=-F2×∆t
F1=-F2
Action = Reaction,w hich is the third law of motion.
Therefore,2nd law of motion is a real law of motion.
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The answer about the importance of the second law lies more in the way it related force or external effort to acceleration, rather than speed as one might think intuitively ; more so when muscle power was the only source of movement on land.
In that time , or even now while walking running or riding a bicycle; one quickly reached a steady speed without experiencing the push of acceleration . Thus , the concept of changing speed being the result of an applied force rather than a higher speed , changed the way in which motion could be analysed very dramatically and successfully.
This is one facet of the importancee of the second law. The other is the fact that it tells us a method of analysing the effect of an external force on a body in various situations and telling us whether or not all the forces acting have been taken into account.