The of tangent on position-time graph represents the velocity of the particle.
Note: If the graph is plotted between distance and time, then it is always an increasing curve. The graph never comes back towards origin because distance never decreases with time.
Slope = 0, velocity = 0, i.e., line parallel to time axis represents that the particle is at rest.
Slope is infinite hence velocity is infinite, i.e., line perpendicular to time axis represents that particle is changing its position but time does not changes it means the particle possesses infinite velocity.Practically, this is not possible.
Slope is constant and positive hence velocity is constant, i.e., line with constant slope represents uniform velocity of the particle.
Slope is increasing, velocity is increasing, hence acceleration is positive.
Slope is decreasing, velocity is decreasing hence acceleration is negative.
Slope is positive but constant. Hence, acceleration will be positive when particle moves away from the point of reference (positive displacement).
Slope is negative but constant. Hence, acceleration will be negative, i.e., line with negative slope represent that the particle returns towards the point of reference (negative displacement).