The distance between two corresponding parts of a wave is its

Wavelength

Explanation:

The distance between two corresponding parts of a wave is its WAVELENGTH. Wavelength can also be termed as the distance between two successive crest and trough of a wave. It is expressed as the ratio of the velocity of the wave to its frequency. As such the wavelength cannot be determined without movement of the wave, the wave has to be in motion because this is what will produce the needed velocity and frequency.

conduction, convection, radiation

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.