The Fundamental Relationship:

* Velocity (v) is the rate of change of an object's position.

* Acceleration (a) is the rate of change of velocity.

* Time (t) is the duration over which these changes occur.

The Equations:

The basic equations of motion link these three quantities:

* v = u + at (where 'u' is initial velocity)

* v² = u² + 2as (where 's' is displacement)

Why You Need Acceleration or Time:

* No Acceleration: If acceleration is zero, the velocity remains constant. To find this constant velocity, you'd need the object's initial velocity or its displacement over a given time.

* No Time: Without knowing the time interval, you can't calculate the change in velocity. Even if you know the acceleration, you don't know how long it acted to change the object's velocity.

Example:

Imagine a car moving at a constant speed. You know its velocity at one moment, but you don't know its acceleration or how long it's been moving at that speed. You can't determine its velocity at a later time.

Conclusion:

Finding velocity requires information about either the acceleration or the time over which the velocity changes. Without one of these, you can't calculate velocity.