How can I calculate the Newton's second law?

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Answer 1 · 2018-04-09T07:07:26

Newton's second law states that external force $F$ is directly proportional to the rate of change of momentum.

If initial velocity of an an object of mass $m$ is $u$ and after applying uniform force for $t$ seconds, its reaches a final velocity becomes $v$ ,

then its initial momentum is $mxxu=m u$ and final momentum is $mxxv=mv$ and hence change in momentum is

$mv-m u=m(v-u)$

and as it has taken $t$ seconds, rate of change of momentum is $(m(v-u))/t$

But in case of uniform accelaration $a$ , we have $v=u+at$

or $(v-u)/t=a$ and then rate of change in momentum is $ma$ ,

hence $Fpropma$

Now we can choose or define a unit of force that corrsponds to unit mass and unit accelaration and then we will have

$F=ma$