Retardation is the negative acceleration of an object
In a speed-time graph, retardation is calculated from the slope of the graph
Formula: Retardation = change in speed / change in time
Retardation = (final speed – initial speed) / time taken
If the speed is decreasing, the slope of the graph is negative
The magnitude of retardation = absolute value of the slope
For a straight-line graph, use any two points on the line
For a curved graph, find the slope of the tangent at the required point
Units of retardation are m/s² or km/h², depending on the units used for speed and time