Heisenberg, in 1927 pointed out that it is not possible to measure simultaneously both the momentum (or velocity) and the position of a microscopic particle with absolute accuracy. Mathematically this may be expressed
Dp = uncertainity in momentumThe constant on the right side of the equation (the product of the two uncertainties) tells us that the two uncertainties are inversely related. If the momentum of the particle is measured with more accuracy there will be a large uncertainity in its position and vice versa.
Uncertainity is not due to the lack of refined techniques available, but because we cannot observe microscopic bodies without disturbing them. [Observations made as result of the impact of light suffer a change in the position or velocity of these microscopic objects]. This does not hold good for large objects of daily light, as the changes that occur are negligible.