It should be clear that this trip could be made at a constant pace or that the man could run for a while, then stop and admire the scenery, and then go on again. If we consider very short time intervals, we can calculate the instantaneous values for his speed and velocity at specific moments during his trip. Acceleration As mentioned in the last section, motion does not always occur at a constant rate. Motion that is not at a constant rate involves changes in velocity. The time rate of change in velocity gives us a basic working definition for acceleration.
Acceleration is equal to the change in velocity divided by the change in time.
It is possible for the rate of acceleration itself to change as a function of time, but this motion is usually quite complex and is beyond the scope of the mathematical skills required by this course, so only cases of constant, or uniform, acceleration will be considered. That's good, because if you did, you are correct. An important type of acceleration occurs when any object experiences a fall near Earth's surface. This is quite important because it means that if air friction is very small and can be ignored, all objects in free-fall will behave in a similar way and the final velocities and distances dropped in any specific time interval will all be the same, no matter how large or small the objects are. One concept about motion that is often hard for students to grasp is that an acceleration can occur even when the speed or magnitude of the velocity of an object is constant.