# Why is $k$ taken as 1 in the derivation of $F=kma$? [duplicate]

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In the derivation of F=ma, when we reach the point F=kma, we take k=1. Why can't we take 'k' as some other value?

## marked as duplicate by John Rennie, stafusa, Chris♦, valerio, Qmechanic♦Feb 3 '18 at 10:37

We make use of S.I. units. The statement $F=ma$ defines the newton (N) as the force required to accelerate a mass of $1kg$ by $1ms^{-2}$ in the direction of the force. This means that $k=1$.