Distance & Displacement (DP IB Physics) : Revision Note

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Distance & Displacement

Distance

  • Distance is a measure of how far an object travels

  • It is a scalar quantity - in other words, the direction is not important

Total running distance

300 m Race Distance, downloadable IGCSE & GCSE Physics revision notes

The athletes run a total distance of 300 m

  • Consider some athletes running a 300 m race on a 400 m track

  • The distance travelled by the athletes is 300 m

Displacement

  • Displacement is a measure of how far something is from its starting position, along with its direction

    • In other words, it is the change in position

  • It is a vector quantity - it describes both magnitude and direction

Total distance vs total displacement

300 m Race Displacement, downloadable IGCSE & GCSE Physics revision notes

The athletes run a total distance of 300 m, but end up 100 m from where they started

  • Distance is a scalar quantity because...

    It describes how far an object has travelled overall, but not the direction it has travelled in

  • Displacement is a vector quantity because...

    It describes how far an object is from where it started and in what direction

  • When a student travels to school, there will probably be a difference in the distance they travel and their displacement

    • The overall distance they travel includes the total lengths of all the roads, including any twists and turns

    • The overall displacement of the student would be a straight line between their home and school, regardless of any obstacles, such as buildings, lakes or motorways, along the way

What is the difference between distance and displacement?

Displacement v distance, downloadable AS & A Level Physics revision notes

Displacement is a vector while distance is a scalar quantity

  • Consider the same 300 m race again

    • The athletes have still run a total distance of 300 m (this is indicated by the arrow in red)

    • However, their displacement at the end of the race is 100 m to the right (this is indicated by the arrow in green)

    • If they ran the full 400 m, their final displacement would be zero

Worked Example

A professor walks around her garden following the path ABCDA. 

1-1-1-distance-and-displacement-we

Calculate, at the end of their walk

(a) the distance the professor travels.

(b) the displacement of the professor.

Answer:

(a) The distance the professor travels is:

  • The total distance of each side of the rectangle

15 + 9 + 15 + 9 = 48 km

(b) The displacement of the professor is:

  • The displacement is how far the professor is from their original position

  • As they travel back to point A, the total displacement = 0 km

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Ashika

Author: Ashika

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Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.

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