- [Instructor] So let's say we have a sheep
and it is hungry.
So that is my sheep.
My best, quick drawing of a sheep
and it is just following the grass
wherever it finds good grass to eat
and so in pursuit of tasty grass,
it first goes 10 kilometers to the east,
10 kilometers east
and then it takes a right turn
and then it goes five kilometers south,
five kilometers south
and then it takes another right turn
and it goes 10 kilometers west,
10 kilometers west.
My question to you is how far has this sheep traveled?
And pause the video and see if you can figure that out.
How far has that sheep traveled?
Alright, now let's try to answer this together
and it's a little bit of a trick question
because depending how you interpret the idea
how far something has traveled,
there could actually be two valid answers here.
One answer is you could say
what is the total distance traveled?
So let me write this one down.
This is an important concept.
Distance traveled
and this would be the total length of its journey
or the total length of its path.
So the distance traveled in this situation
would be 10 kilometers plus five kilometers,
plus five kilometers plus 10 kilometers,
plus 10 kilometers which would give us 25 kilometers.
That would be 25 kilometers.
So some of you all might have said
that the sheep traveled 25 kilometers.
If that's what you came up with,
what you calculated is the total distance traveled.
Now, some of you might have said, wait, hold on a second,
the sheep was here before
and then it ends up right over here
at the end of its journey
and so its change in position is it would have moved
a net five kilometers south.
From this point to this point
would have been five kilometers south.
It doesn't matter what it did along the way,
what its path was.
At the end of the day, it ended up five kilometers south
of where it started out and this would also be a valid way
of saying how far it traveled
and this notion is known as displacement.
So the displacement would be in this situation
five kilometers south.
So pause this video.
What do you think is the definition or the difference
between saying the distance something traveled
versus its displacement?
Well, as we mentioned, the distance something travels
is the entire length of its journey.
It's the entire path and this thing will never be negative.
You could travel zero kilometers but as long as you are,
your position keeps changing, this thing will only increase
because it's the total length of your path.
Your displacement is your change in position
and since it's a change in position,
not only will we mention the five kilometers,
we'll say in what direction.
The position of the sheep has changed five kilometers
to the south.
So let me write this down.
This is total length of path,
total length of path is the distance traveled
while the displacement is the change in position,
change in position.