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Reef and Granny

Stage: 2 Challenge Level: Challenge Level:1

Reef and Granny


This is a reef knot:

reef knot



And this is a granny knot:

granny knot


Before you read any further, it might be a good idea to make a reef knot and a granny knot. You do not need coloured string - it can even be done with shoelaces!

Can you see any differences between them?

When a reef knot is pulled tight it looks like this:

reef knot pulled tight


When a granny knot is pulled tight it looks like this:

granny pulled tight 1


... or this:

granny pulled tight 2


or this:

granny pulled tight 3


Which do you think is the best knot for making things secure?

Why?

Why do this problem?

Knots are a fascinating subject and this problem is a good way to begin exploring them. It would be well worth watching the video What's a Knot? with your class in addition to having a go at this problem.

This problem is probably best approached in a very practical way with children - giving them some string to tie the knots for themselves. However, before this, encourage your pupils to predict which knot will be best and why. If they take time to hypothesise they will get a lot more out of the practical task.

Following on from this activity, you might like to look at Turning Granny which invites learners to look at using symmetry to distinguish between knots.

Key questions

How do you think you can tie that knot?
If you want to make things secure with a knot, what do you think is important?
Why don't you try tying two things together using each knot to test which knot stays in the same shape?
Do you think that this will make it less likely to slip?

Possible extension

Learners could have a go at this problem

Possible support

Suggest using this information with real string:
To tie a reef knot you take an end of the string in each hand and do 'right over left, left over right'. A granny knot is 'right over left, right over left again'.