Why does the change in only the direction leads to acceleration of a body. I mean acceleration of body implies that it is moving fast or getting slow with respect to its initial speed. But i dont think that change in direction affects any of it?
It's not just about total speed, it's about the speed in each direction -- i.e. the velocity vector.
If I'm driving east at 60kph, and I turn left using a turn of some radius, but maintain the same velocity to end up going north at 60kph, my direction changed, but my total velocity remained constant. But my velocity in the eastward direction decreased from 60kph to 0kph, which means there was an acceleration in the westward direction. My velocity in the northward direction increased from 0kph to 60kph, which means there was an acceleration in the northward direction. Around such a curve, the acceleration is a vector pointing inward.