- Average acceleration over a period of time is defined as the total change in velocity in the given interval divided by the total time taken for the change.
- For a given interval of time, it is denoted as

$\stackrel{\u2013}{a}$.

- Mathematically,

$\stackrel{\u2013}{a}=\frac{{v}_{2}\u2013{v}_{1}}{{t}_{2}\u2013{t}_{1}}=\frac{\u2206v}{\u2206t}$Whereandare the instantaneous velocities at timeandandis the average acceleration.

- In the velocity time graph shown above, the slope of the line between any time interval t
_{1}and t_{2}gives the average value for the rate of change of velocity for the object during the time t_{1}and t_{2}

In a velocity-time curve, the instantaneous acceleration is given by the slope of the tangent on the curve at any instant.

Consider the velocity-time graph shown below:

- Here, between the time intervals of 0 – 2 seconds, the velocity of the particle is increasing with respect to time. In other words, the slope of the v -t curve in this time interval is positive. So it experiences a positive acceleration.
- Between the time intervals of 2 – 3 seconds, the velocity of the object is constant with respect to time. slope of the v -t curve in this time interval is 0. So, the body experiences zero acceleration.
- Consider the time intervals between 3 – 5 seconds. The velocity of the body decreases with respect to time. In other words, the slope of the v -t curve in this time interval is negative. So, the body experiences a negative value of acceleration.

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