The velocity-time (v-t) graph shown below illustrates

In a velocity-time (v-t) graph, the slope of the line represents the acceleration of the object [t1, t6]. A straight line indicates that the rate of change of velocity is constant, signifying uniform motion [t1, t6]. Specifically, if the slope is negative (downward sloping), it indicates that the velocity is decreasing at a constant rate over time [c1, t8]. This constant negative acceleration is defined as uniform retardation or deceleration [t1, t3]. While an upward-sloping straight line represents uniform acceleration, a downward-sloping straight line represents uniform retardation [t6, t8]. Non-uniform motion would instead be represented by a curved line, indicating a changing rate of acceleration or retardation [t1, t2, t5]. Therefore, a straight line with a negative gradient illustrates uniform retardation.

Sources

1. [1] https://satheeneet.iitk.ac.in/article/physics/physics-velocity-time-graphs/
2. [2] Microeconomics (NCERT class XII 2025 ed.) > Chapter 2: Theory of Consumer Behaviour > EXAMPLE 2 > p. 22