Question

how does the second law of motion give us a method to measure force

Answer 1

See what 2nd law says is rate of change of momentum is directly proportional to force applied hence..
F = (mv1-mv2)/t
F= m(v1-v2)/t
now velocity / time = acceleration ..
thus F = ma
hence we got method to measure force buddy..

Answer 2

Answer:

The second law of motion gives us a method to measure the force acting on an object as a product of its mass and acceleration. That is, when F = 0, v = u for whatever time, t is taken. This means that the object will continue moving with uniform velocity, u throughout the time, t.