According to the Copenhagen interpretation of quantum mechanics, when a measurement is made on a particle, the wave function representing the particle's state collapses. This collapse refers to the reduction of the wave function from a superposition of possible states to a single definite state corresponding to the measurement outcome.
The collapse of the wave function occurs because the act of measurement disturbs the particle and affects its state. When we measure a particle's position, for example, the wave function collapses to a localized state corresponding to the position measurement outcome. Similarly, when we measure a particle's momentum, the wave function collapses to a state corresponding to the momentum measurement outcome.
Heisenberg's uncertainty principle states that there is a fundamental limit to the precision with which certain pairs of physical properties, such as position and momentum, can be known simultaneously. This uncertainty arises due to the wave-like nature of particles in quantum mechanics. The uncertainty principle implies that the more precisely we try to measure one property (e.g., position), the less precisely we can know the other property (e.g., momentum).
Therefore, when we make a measurement to be more certain of a particle's momentum or position, the wave function collapses, and we obtain a specific value for the measured property while sacrificing knowledge about the other property due to the inherent uncertainty.