1. Change in Speed:

* Acceleration: This is the most common way. Acceleration is the rate of change of velocity over time.

* Positive acceleration: Means the object is speeding up.

* Negative acceleration (or deceleration): Means the object is slowing down.

* External forces: Forces acting on an object can cause it to speed up or slow down. Examples include:

* Gravity: pulls objects towards the Earth, causing them to accelerate downwards.

* Friction: opposes motion and causes objects to slow down.

* Thrust: a force that pushes an object forward, like the engine of a car.

2. Change in Direction:

* Turning: When an object changes direction, even if its speed remains constant, its velocity changes. This is because velocity is a vector quantity, meaning it has both magnitude (speed) and direction.

* Curvature of path: Objects moving in curved paths, like a car going around a corner, experience changes in velocity even if their speed is constant.

In Summary:

A change in velocity occurs when there is a change in speed, a change in direction, or a combination of both. These changes are caused by external forces acting on the object, causing it to accelerate or change its direction of motion.