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## High school physics

### Course: High school physics > Unit 1

Lesson 2: Distance, displacement, and coordinate systems- Distance and displacement introduction
- Distance and displacement in one dimension
- Position-time graphs
- Worked example: distance and displacement from position-time graphs
- Finding distance and displacement from graphs
- Distance and displacement review

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# Distance and displacement introduction

An introduction to the difference between distance traveled and displacement. Created by Sal Khan.

## Want to join the conversation?

- Would it be correct to say that displacement is the end-point, the last stop?(13 votes)
- Not exactly. Displacement is the shortest distance from your initial position to your final position. Therefore, displacement is a measurement of distance and not an "end-point."(29 votes)

- If it didn't go 10 km west, you would use the Pythagorean theorem, right(2 votes)
- pythagorean theorem is used only when the object turns about only in 90 degrees(3 votes)

- If the sheep traveled 10km east, 5km south, 10km west, and then 5km north will the displacement be 0?(5 votes)
- Yes, because the sheep will walk in a square, therefore, the starting position and ending position will be the same, so the displacement is zero because 0-0=0(11 votes)

- Why would it not be correct to say that the sheep travelled -5 km south?(2 votes)
- What you are doing by saying -5 km south is giving the direction twice: the first time by denoting the "-" symbol before the five and a second time by saying "south." You want to use only one method of indicating direction.

This can be done by using a positive/negative symbol or by using a direction word such as north, up, down, west etc.(17 votes)

- i did not understand the exact meaning of displacement?(3 votes)
- Displacement is the final distance of a point from the initial point.

For instance, if I walked 10 meters from my house, then walked 5 meters towards my house, my displacement from my house would have been 5 meters, even though I walked 15 meters in total.

Displacement is more of an a-to-b measure, rather than a how-did-a-get-to-b measure, if that makes more sense.(14 votes)

- From4:12we can say that the * definition of displacement is "change in position" * and for * distance is "total length of path travelled" * ?(6 votes)
- Well yes we can that displacement refers to the change between the initial and final position and distance refers to the whole length of path covered by an object(5 votes)

- This might not be totally on topic, but...

I've noticed some people here in the comments mentioning the Pythagorean Theorem as a reference to the problems in this lesson. While I am familiar with the theorem itself, I have no idea how that would apply here.

Could somebody explain how you use the Pythagorean Theorem in physics?

Sorry if this is a silly question-this is my first time studying physics (and I'm lousy at math) :)(5 votes)- You can use the pythagorean theorem to find the distance between any two points on a coordinate plane as part of the distance formula. People are just mentioning that if the sheep hadn't gone West you would've needed to use the distance formula to figure out the displacement of the sheep because it wouldn't have been immediately obvious.(4 votes)

- i would have to say that some people would use the Pythagorean theorem, but in answer to the question the displacement would have to be from the starting point to the end point which is where it was trying to go in the first place correct(4 votes)
- What is the difference b/w velocity and speed?(3 votes)
- Velocity is a vector quantity meaning that it has both a magnitude and direction. (For example, you might say that moving right is positive and moving left is negative. So, if you are moving 5 m/s to the left, you are moving -5 m/s.) Speed is a scalar quantity so it has only a magnitude. (To refer to the previous example, it would not matter if you are moving left or right. The speed would simply be 5 m/s.)(5 votes)

- In answer to the question at3:00, would it be valid to say that displacement is the distance between the initial point and the final point? Thanks!(2 votes)
- You are almost correct. Remember, displacement is a
**vector**quantity, meaning that you have to take into consideration the direction in addition to the change in position. That means you would need to subtract the initial point from the final point. It is important to include the correct sign (+ or -) depending on your direction.(1 vote)

## Video transcript

- [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.