The distance time graph of a body moving at uniform speed is always a straight line.
Consider the following graph.
In order to analyze the motion we consider three segments OA, AB and BC.
gives the slope of the displacement time graph and that is equal to the velocity.
The speed –time graph of a body is a straight line parallel to the time axis.
When the speed of the body changes in an irregular manner, then the speed-time graph of the body is a curved line.
Consider the following velocity-time graph:
Acceleration is the rate of change of velocity represented as:
$a=\frac{dv}{dt}$In other words, slope of the velocity time graph represents acceleration. In the given graph, acceleration is positive in OA and CD while it is negative in the region AC. Also the velocity changes direction at B.
We know that,
$dx=\int vdt$Graphically it means area under velocity-time graph represents displacement.
So,
.
Velocity time graph can also go below x-axis but not speed time graph because speed is never negative.
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