I'm trying to understand the Uncertainty Principle, for the case of momentum and position, but I'm stumped. Suppose one can measure the position of a particle with arbitrary precision. Suppose the measurement of this particle's positions were made at time t= 0 and then time t=1. The vector length of the particle path divided by time then would yield the velocity of the particle at time t=1, per definition. If the mass of the particle was also constant then per definition mv= momentum should yield the exact momentum of the particle at t=1 , no? If the above is accurate, how does one get to an Uncertainty Principle? I'm sure the math leads to this Principle but I'm having a hard time relating it physically.