The relative velocity between two bodies changes when they are moving towards each other due to the effect of their individual velocities combining.
When two bodies are moving towards each other, their velocities have opposite directions. As a result, the relative velocity is the vector difference between their individual velocities. The magnitude and direction of the relative velocity depend on the magnitudes and directions of their individual velocities.
If the two bodies have the same magnitude of velocity but opposite directions, the relative velocity would be the sum of their velocities. For example, if Body A is moving with a velocity of 5 m/s towards Body B, and Body B is moving with a velocity of 3 m/s towards Body A, the relative velocity between them would be 8 m/s towards Body A.
On the other hand, if the bodies have different magnitudes of velocity, the relative velocity would be the difference between their velocities. For example, if Body A is moving with a velocity of 7 m/s towards Body B, and Body B is moving with a velocity of 4 m/s towards Body A, the relative velocity between them would be 3 m/s towards Body A.
In summary, when two bodies are moving towards each other, their individual velocities combine to determine the relative velocity. The relative velocity reflects the difference between their velocities and may have a different magnitude and direction than their individual velocities.