Rivers and coasts
Rounding pebbles: attrition in a jar
Does shaking wear rock fragments rounder and smaller?
Watch first
An English teaching video on this topic from iNewittAll. Watch it, then scroll down for the lesson.
What you need
Tick each one as you find it — 0 of 5 ready.
Plan the fair test
- Change: Total shaking time in minutes
- Measure: Mass or longest length of the fragments
- Keep the same: Same jar, same water volume, same shaking speed, control fragments untouched
Objectives this evidences
- Understand rivers, coasts and glaciation and the physical processes that give rise to landscapes, and how they change over time
Do it, one step at a time
Step 1 of 5
- Step 1. Weigh or measure your six fragments and sketch their shape.
- Step 2. Put three in the jar with 200 ml of water. Keep the other three dry and untouched as your control.
- Step 3. Shake steadily for one minute, then drain, dry, re-measure and sketch again.
- Step 4. Repeat for two, four and eight minutes of total shaking, measuring after each stage.
- Step 5. Plot total shaking time against mass, and describe the shape change in words.
What should happen
Fragments get smaller and noticeably rounder. This is attrition, which is why pebbles far downstream and along a beach are rounder and smaller than the angular rock upstream.
Think about: Sugar dissolves as well as breaking. Which of your two processes — solution or attrition — is doing the work?
Write up your result
A sentence or two is enough to save it.
The lessons behind this practical
Each one opens with the same short film, and the film has a written transcript underneath if reading is easier than watching.
Now the quiz for this topic
Questions come from the lessons behind this practical, so nothing is asked that has not been taught.
Quiz
Rivers and coasts quiz
4 questions from the lessons in this stage. No timer, and you can try again as many times as you like.