How this calculation works
Velocities must be measured along the same axis and use the same sign convention. This returns average acceleration over the interval; instantaneous acceleration may vary.
Average acceleration = (final velocity − initial velocity) ÷ timeA worked example
Changing from 0 m/s to 20 m/s over 5 seconds gives 4 m/s².
Good to know
Assumes the idealized model described above. Use consistent units and independently verify figures before a consequential decision.
A negative value need not mean slowing down
If motion is already in the negative direction, a negative acceleration can increase speed in that direction. “Negative” describes the chosen axis, while “slowing” describes a decrease in speed magnitude. They are not interchangeable words.
For example, changing from −5 m/s to −15 m/s over 5 s gives −2 m/s² even though speed increases from 5 to 15 m/s. The sign convention carries information about direction.
An average can hide changing acceleration
A start velocity, end velocity and total duration determine average acceleration. They do not tell you whether the acceleration was constant at every instant. Different motion histories can share the same endpoints.
Use velocities along the same axis, with seconds for elapsed time. A nonzero positive duration is required; acceleration cannot be found from a zero-time denominator.
A few questions, answered
Can the initial velocity be negative?
Yes. Use signed values consistently along a chosen axis.
Does this calculate acceleration from distance alone?
No. The input model uses initial velocity, final velocity and elapsed time.