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Unformatted text preview: e. This is, in fact, how
Newton originally stated his second law of motion. Starting from the more common version of the second
law, we have ∆
∆ 1 ∆ ∆ (3) where the mass m and the forces are assumed constant. This would not be the case if we take relativity
into account or if we work out problems such as a rocket being launched. However, for this experiment,
we will not be dealing with relativistic speeds and we will not be dealing with situations in which we have
a change of mass. Thus our assumption is correct, mass is constant.
By looking at the term in equation (3), we can see that mv is the definition of the momentum.
Thus we can say that: The change in an object’s momentum divided by the elapsed time equals the
constant net force acting on the object: ∆
∆ (4) or if you assume that the change is infinitesimal and you have had calculus we can write it as (5)
These two equations are valid when the forces are not constant, provided the limit is taken as Δt becomes
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