Video Transcript
The positions of two objects are
shown at one-second time intervals, starting at a time of zero seconds. Between two seconds and three
seconds, which object has the greater average speed?
Another way that we can think about
this diagram showing the objects’ motion is to imagine that the objects are leaving
marks on the ground at regular intervals. So, we can reimagine the diagram to
look like this. We represent objects A and B as
dots, and that avoids confusion about their relative positions. Then labeling each dot so that it
represents when that mark was made, we can begin to understand the objects’ relative
speeds.
Remember, speed is the measurement
of the distance that an object moves over some quantity of time. Here we see that object A moves the
same amount of distance in each time interval. Therefore, we can say that object A
moves with a uniform or constant speed. Each snapshot taken one second
apart is an equal distance apart. So, the object never moves more or
less distance than in the previous second. Object B, on the other hand, always
covers a different distance between intervals. Object B starts out slow, covering
very little distance in one second, but it ends up moving very fast, covering lots
of distance in one second.
To know when the objects are moving
at the same speed since the time intervals are always the same, we need to look at
how much distance they move between intervals and compare. Look at this diagram, annotated
with the objects’ relative speed. Between zero and one second, object
A moved more distance than object B. So, we can say it moved faster. Between one to two seconds, B moved
more distance than A. So, we can say it moved faster. And between two to three seconds, A
and B moved by the same amount. This must mean then that they moved
at the same speed between two and three seconds. So, the correct answer here is that
the average speeds are the same between two seconds and three seconds.
