The Concept of Instantaneous Velocity The concept of instantaneous velocity really becomes counter-intuitive to me when I really think deeply about it. Instantaneous velocity is the velocity of something at an instant of time; however, at the very next instant the velocity changes. In general, speed tells us how quickly something is changing its position with respect to some point in space. Then by instantaneous velocity we mean that the object at some instant is changing its position with respect to time, but may change to a velocity much faster. But if it is changing its position with that rate then the time passes by and that instant as well and at another instant the velocity is different. Did it even move with that velocity for a moment? I’m sorry that I’m not exactly able to tell you what my problem is; however, it is something like I've described. 

Anything that changes in speed will do so as a result of momentum transfer into the object. This requires some interaction with other forces. Force fields are the source of momentum transfer, this transfer takes some time, thus we get acceleration.
