Round the track: distance and displacement
Run part of a lap, a whole lap and more round a 400 m track. Compare the distance you ran with your displacement, and your average speed with your average velocity.
Core concept
Distance is the length of the path travelled; displacement is the straight-line distance from the start to the finish, in a direction; after a whole lap the distance is 400 m but the displacement is zero
Topic: Force and motion
When you run round a track, two different things can be measured. The distance is how far you actually ran along the curved path. The displacement is how far you are from the start in a straight line, and in which direction. Distance has only a size (a scalar quantity); displacement has a size and a direction (a vector quantity). In the same way, average speed: How far something travels in a certain time, like kilometres per hour. All key words is distance ÷ time, while average velocity is displacement ÷ time. In this lab you run on a round track 400 m long (its radius is 63.66 m), starting at the bottom and going anticlockwise.
What you will learn
- Distinguish between distance and displacement.
- Distinguish between speed and velocity, and between scalar and vector quantities.
- Work out displacement on a circular track.
- Explain how a body can travel a long distance with zero displacement.
Before you start
- Know that speed = distance ÷ time.
Materials
- A school ground or a stadium track
Equipment
- A measuring tape, a stopwatch, chalk to mark the start
Procedure
- Run a quarter lap and record.
- Run half a lap and record.
- Run one whole lap in 60 s and record.
- Run two laps and record.
How this simulation is simplified
- The track is a circle 400 m round (radius 63.66 m); real tracks have straight sides.
- The runner keeps to the inside line of the track.