Answer :
Final answer:
A dial indicator is the most appropriate tool to measure the alignment of a rotor shaft or the plane of rotation of a disk. It provides precise measurements of deflection which are necessary for ensuring machinery precision.
Explanation:
To measure the alignment of a rotor shaft or the plane of rotation of a disk, the appropriate tool to use would be a dial indicator. This precision instrument can gauge small amounts of deflection or deviation, which are common when assessing the axial and radial run-out of shafts or disks. A Protractor could be used for measuring angles but is not suited for alignment measurements. A shaft gauge might be used in some contexts, but it is less common and not as precise for this specific purpose. A dial indicator provides a direct measurement of the movement of the rotor shaft as it rotates and can show whether it moves out of alignment, which is crucial for machines that require high levels of precision. During experiments to observe uniform circular motion, measuring tools like a timer and a ruler are used to find the linear or angular velocity and the radius of curvature. While a spring scale might be useful in measuring forces, for this particular question concerning rotor shaft alignment or disk rotation, the dial indicator is by far the most suitable instrument.
