Video Transcript
Fill in the blank. An object is accelerating when its
speed is (A) increasing, (B) decreasing, (C) increasing or decreasing.
Let’s say we had an object here
whose speed over time is increasing. This means if we looked at the
position of the object at one second intervals, the distances between the positions
of the object would increase. We can recall that acceleration is
defined as a change in speed over a change in time. Therefore, this object whose speed
is increasing over time is accelerating. But notice that for an object’s
speed to change, it doesn’t necessarily need to increase.
Say we had a second object here and
that we knew the positions of this object at zero, one, two, and three seconds. In this instance, the distances
between the object positions with time are getting smaller. But still the speed of the object,
Δ𝑣, is changing. We can say that the speed of the
pink object is decreasing. The particular name given to an
object whose speed decreases over time is deceleration. We can think of deceleration as
negative acceleration. It’s a type of acceleration. Since an object’s speed will change
whether it’s speeding up or slowing down, we can answer that an object is
accelerating when its speed is increasing or decreasing.
