* Change in velocity: Acceleration is the rate of change of velocity. This means that if an object's velocity is changing (either in speed or direction), it is accelerating.

* Net force acting on the object: According to Newton's Second Law of Motion, the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. This means:

* Larger net force = Larger acceleration

* Larger mass = Smaller acceleration

* Slope of a velocity-time graph: The slope of a velocity-time graph represents the acceleration. A positive slope indicates positive acceleration (increasing velocity), a negative slope indicates negative acceleration (decreasing velocity), and a horizontal line indicates zero acceleration (constant velocity).

In summary, any of the following indicate that an object is accelerating:

* A change in speed.

* A change in direction.

* A net force acting on the object.

* A non-zero slope on a velocity-time graph.