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Ellen's moments

  • Key Stage 3
  • Popular Activity
  • Topical

Type: Activity
Learning Strategy: Case study
Topic: Forces

Ellen MacArthur demonstrated amazing skill, determination and endurance in her record-breaking circumnavigation round the world. But why didn't her – inherently unstable – multi-hull yacht capsize? In this activity students explore the moments of force on multi-hull and keel- boats. They then advise Ellen's rival which type of boat to buy.

Published: 17th February 2005
Reviews & Comments: 3

Learning objectives

� Students will be excited by physics, and realise the usefulness of the laws of physics in extreme sports
� Students will use the principle of moments to explain why sailing boats balance

Try the activity

You will need Acrobat Reader installed to open the activity sheets.

� 9L pressure and moments – use the principle of moments to explain a range of situations

Running the activity

Suggested time: 20 minutes

Possible starter:
Ask students to list, in pairs, three dangers that Ellen MacArthur faced on her record-breaking round the world trip. Take feedback. Then show students page 1, which emphasises the dangers of strong winds and instability. Page 1 can either be projected or displayed as an OHT.

Main activity:
Set the task by showing students page 2 – ask students to use the information on this page and page 3 to decide whether Ellen's rival should buy a keelboat or a multi-hull boat. As well as planning what to say, students can draw diagrams to support their decisions. They also need to plan how to answer Ellen's rival's questions, which are in 'thought bubbles' on page 3.

Ask some students to report on what they will say to Ellen's rival. Take a class vote on which type of boat he should buy.

Further information:
When wind blows against a boat sail, it doesn't naturally blow the boat along. It would be much more normal for the boat to blow over. The force of the wind on the sail produces a large turning moment that makes the boat rotate, and fall over. To keep the boat upright and sailing there has to be a turning moment in the other direction to keep the mast upright.
This activity highlights two types of boats:

These have a big heavy weight under the boat, made of a very dense metal such as lead. As the boat gets pushed over by the wind this gets pushed up to produce an opposite turning force to the sail and mast. So the boat doesn't fall over. If the boat does fall over, it may still be possible to right it again.

2. Multi-hull boats
These have additional buoyancy hulls on the sides of the main hull, which are held there by arms. When the boat heels over due to the wind on the sails, the buoyancy of these makes a turning force to keep the boat upright. Multi-hulls are lighter than equivalent sized keelboats, and so are faster in almost all wind conditions – sometimes by as much as 50%. If a multi-hull boat is flipped over, it cannot be righted.

Even so the skipper (Ellen) had to keep a constant watch to balance the turning effect of the wind on the mast. Disasters can strike if the wind gets too strong. Ellen monitored the pressure of the wind on the sail, and reduced the sail area if the wind got stronger.
This reduced the force pushing the boat along – but also reduced the chance of it getting pushed over.

News links

Team Ellen
There is comprehensive information about Ellen MacArthur's record-breaking journey at this site.
Mulithull pages
This site has information about multi-hull boats
The Times Herald
This has some useful information about keelboats

Reviews & Comments

Write your online review to share your feedback and classroom tips with other teachers. How well does it work, how engaging is it, how did you use it, and how could it be improved?


Apr 10th, 2008

5 Star

This was an excellent change for teaching about and applying the idea of moments outside of the classroom.

Reviewer: jonathan watters

ellen's moments

Jul 19th, 2006

4 Star

Relevant and topical -real life and science. Really enjoyed the fact that pupils can relate to a topic that some find difficult to comprehend.

Reviewer: Joanna Rutter

Ellens Moments is great!

Mar 20th, 2005

4 Star

I thought this activity was excellent to get the pupils really engaged in the topic of moments, which is quite a tough topic to make interesting to them! They loved the fact that the "boring science stuff" was made relevant to a very recent and topical event and this really helped them to relate the science to everyday situations. The questions they had to answer really got them thinking. Excellent!

Reviewer: Kat Holtom

The upd8 store
200 lessons and assessments from as little as £4.95

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