2. Second Law of Motion
According to this law, the rate of change of momentum (mass × velocity) of a body is proportional to the impressed force and it takes place in the direction of the force.
Mathematically ∝
⇒ = k =
(Defining force such a way that k = 1)
= (m) = m
= m
In scalar form, F = ma
(i) Force is a vector quantity, whose unit is Newton or (In Mks)
and Dyne or (In C. G. S.)
(ii) The dimension of force is [MLT ^–2]
(iii) The second law of motion gives the magnitude and unit of force.
(iv) If m is not constant
= (m) = m +
As in case of rocket propulsion, the mass of the fuel varies with respect to time.