Distance and Displacement Video Lecture - Class 9

In this video we are going to talk about the
difference between distance and displacement.
If this car moved from Point A to Point B
we could say it traveled a total distance
of 100 meters. Distance is a measurement of
the length between two points. Now let's go
back to this example and add another road
sign here, let's bring this one in so we have
a direction. If the car again travels from
Point A to Point B, we can say that it traveled
a distance of 100 hundred meters but we can
add in another part of this measurement. We
could say it traveled 100 meters to the east
and this is actually a displacement rather
than a distance. The difference is that we're
including a direction this time around. Now
the definition for displacement is the overall
change in positions so we are looking at a
starting position and comparing it to a finishing
position. And then the other big difference
here is that displacement's going to include
a direction. Now displacement includes a direction
and so we call this measurement a vector and
so measurements that include directions are
called vectors. Distance doesn't include a
direction and so it's called a scalar. Let's
add another road sign here in our example
so if we add this extra midpoint here roadsign
and we bring our car back to Point A, the
car travels from Point A to Point B and then
just backs up here to the center here. Let's
see how far it traveled. Now it's traveled
a distance there from Point A to Point B of
100 meters and then it traveled an additional
50 meters for a total distance of 150 meters.
Now if we look at its displacement; however,
we're comparing its starting position which
is right here to its finishing position which
is right here and so its total displacement
would be 50 meters to the east. In other words,
it's 50 meters east of where it started which
was right here. Let's look at another example
here. If you've ever run track and field you
may have had the chance to run the 400 meter
race. The 400 meter race is one lap around
the track and for a total distance of 400
meters. Now what would the displacement be?
Well if we compared your starting position
right here to your ending position right here
we would say that your total placement was
0 meters and it's almost like if you were
running the race and all the fans just shut
their eyes as soon as the gun went off and
then opened them again when it was all over
and it looks like you're in the exact same
location. Your displacement is 0.