To get a good probability of finding the particle in a small region of space from a wave-like probability distribution, we can combine waves of different wavelengths such that they interfere constructively (page 66) in just that region but destructively everywhere else. This localized wave is called a wave packet. To increase the localization and get a more tightly defined position for the particle, we must add more waves. But the wavelength determines the particle’s momentum. So the more waves there are, the more possibilities there are for a measurement of momentum.
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