Final answer:
A skateboarder reducing speed when moving up a hill is an instance of negative acceleration, where deceleration specifically refers to acceleration in the opposite direction to velocity.
Step-by-step explanation:
An example of negative acceleration is a skateboarder who reduces speed when moving up a hill. This is because negative acceleration occurs when an object's acceleration is in the opposite direction to its motion, causing it to slow down. It's important to note that negative acceleration does not necessarily mean the object is decelerating; it depends on the chosen coordinate system.
When considering the concept of acceleration, we understand that it indicates any change in velocity, which includes speeding up, slowing down, or changing direction. In physics, deceleration specifically refers to acceleration that is in the opposite direction to the object's velocity, invariably leading to a reduction in speed.