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### Course: Class 11 Physics (India)>Unit 6

Lesson 1: Distance, displacement, and coordinate systems

# Distance and displacement introduction

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

## Want to join the conversation?

• If it didn't go 10 km west, you would use the Pythagorean theorem, right
• Everyone else on Pythagorean's Theorem: Yes, it makes sense!

Me: Why are we still here, just to suffer...
• Would it be correct to say that displacement is the end-point, the last stop?
• 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."
• i did not understand the exact meaning of displacement?
• 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.
• If the sheep traveled 10km east, 5km south, 10km west, and then 5km north will the displacement be 0?
• 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
• Why would it not be correct to say that the sheep travelled -5 km south?
• 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.
• From we can say that the * definition of displacement is "change in position" * and for * distance is "total length of path travelled" * ?
• 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
• Did the sheep get its food at the end?
• hopefully it did.
• What will happen if it moved 8 Km west instead? how would you find that?
• If you mean that after moving five kilometers to the south, then move eight kilometers to the west, you can find it by using the Pythagorean law and trigonometry.
• 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) :)