Video Transcript
Fill in the blanks: A displacement
is a distance in a particular direction. Displacement is the blank quantity
of change of blank. (A) Scalar, speed. (B) Vector, speed. (C) Scalar, position. Or (D) vector, position.
We want to figure out which of
these answer choices correctly fills in the two blanks in our sentence. That sentence is about
displacement, and we’re told that a displacement is a distance in a particular
direction. So if we were given a distance, say
a distance of five kilometers, and also told a direction to go along with the
distance, then taking these two things together, we have a displacement, a distance
in a particular direction. The first blank in our sentence
will be filled either with the word vector or scalar. A vector is a physical quantity
that has magnitude as well as direction. A scalar, however, has magnitude
but no direction. Since displacement has magnitude
and direction, it’s a vector quantity. We can fill in the first blank in
our sentence and cross off answer options (A) and (C).
To fill in the second blank, we’ll
need to know whether displacement is a change of speed or a change of position. Working with our example
displacement of five kilometers to the north, an object could be displaced this
amount by starting out, say, here and then moving a distance of five kilometers to
the north. So at first, the object’s position
was here, and then after being displaced, its position was here. Displacement then has to do with
change of position rather than change of speed. We choose answer (D). And our completed sentence reads
“Displacement is the vector quantity of change of position.”
