Final answer:
When an object experiences a decrease in velocity, it is undergoing negative acceleration, which is commonly known as deceleration. This occurs when the acceleration is in the opposite direction to the object’s velocity, regardless of the actual travel direction of the object.
Step-by-step explanation:
When an object's velocity decreases, this is typically referred to as negative acceleration or deceleration. It is important to note that deceleration is a type of acceleration; specifically, it is acceleration that is opposite in direction to the velocity of the object. For instance, if an object is moving to the right (positive direction) and slows down, this slowing down represents a negative acceleration because the acceleration is to the left (negative direction).
In physics, negative acceleration does not necessarily mean the object is moving in a negative direction; it simply indicates that the speed of the object is decreasing. The negative acceleration is in the direction opposite to that of the object's motion. For example, if a car is moving eastward and begins to slow down, it is experiencing negative acceleration, even though it is still moving east.