Task: Question Answering
Input (English): Background Paragraph: Acceleration is a measure of the change in velocity of a moving object. It measures the rate at which velocity changes. Velocity, in turn, is a measure of the speed and direction of motion, so a change in velocity may reflect a change in speed, a change in direction, or both. Both velocity and acceleration are vectors. A vector is any measurement that has both size and direction. People commonly think of acceleration as in increase in speed, but a decrease in speed is also acceleration. In this case, acceleration is negative and called deceleration. A change in direction without a change in speed is acceleration as well. 
Story: Johnny is playing with a toy train set his parents bought him. The controls for this train set allow him to make it go faster or slower and it even has a rail switch to make it travel on different tracks branching off to the left or right. 
Question: Given Johnny decides to slow the train down, will this be an example of acceleration or deceleration?
Output (English): deceleration.