Letters in STS issue 69, May 2011-
committee structures and limp lettuces!
Committees or no committees? (this topic is further discussed here)
At a recent committee meeting a fellow member said she thought that there were legal
reasons for our dance group being a 'group' rather than a 'club' with members paying a fee
to belong. There are people who consider themselves 'members' of our group when they only
attend about 3 times out of 20 meetings a year. Another local club we attend charges an
annual membership fee, provides membership cards and reduced prices for Saturday night
hops. Only people with paid-up membership can vote at their AGM but at ours anyone who
thinks they're a member can. How much does it matter anyway? What do STS readers or any
legal advisers out there think? Advice gratefully received.
Physics, swinging and limp lettuces.
I have been revising my nuclear physics: people need to learn that we must live within an
energy budget or face unpleasant consequences. Either we boil the Earth by burning
remaining reserves of coal, oil and gas, build more nuclear stations or abandon energy
guzzling lifestyles. I have worked on renewable energy - but it can realistically only
supply a fraction of what we now consume - especially for transport.
However, this is easier than explaining what is wrong with John Sweeney's ideas of what
happens in a circle or swing (STS 68).
First, a body travelling in a circle is accelerating towards the centre at all times. This
is despite that it may be travelling at a constant speed: its direction (and therefore its
velocity) is changing. Therefore it is accelerating. The force needed for this
acceleration is an inward centripetal force. If the force is suddenly removed, the body
will travel not backwards out of the circle but along a tangent. The trebuchet, an ancient
weapon of war, used this principle. After release from the device on a tangential
trajectory, its projectile (sometimes a diseased corpse) would continue in a straight line
in the absence of any imposed force. In practice, it curved downwards back to Earth, with
air viscosity and gravity providing forces. Cruise missiles have a greater range but are
The mistake that John makes is in saying 'Centrifugal force is pulling you away from the
centre of the circle'. This reactive force only exists for the time that any inward
centripetal force operates. Once the string is cut or the swinging dancers part company,
centripetal force vanishes and with it the reactive centrifugal force. Any tendency for
dancers to fly outwards is psychological - or maybe physiological as a consequence of
muscular tension! Some dancers may believe that the centrifugal reaction force still
exists and move accordingly. Of course, we have so called centrifuges - used for
separating cream from milk and various isotopes of uranium - but these utilise centripetal
acceleration and the physics is quite complicated. If you find this easy - try
understanding the Coriolis effect.
However, I couldn't agree more that dancers should learn to 'connect' and not be limp
lettuces. In strip the willow ceilidh dances such as Drops of Brandy there are lots of
fast half circles with bodies briefly yet strongly connected and then flying off at
tangents. A mistake some fast dancers make is to hang on to the elbow turns for too long.
Just let go and let physics do the rest!
Index page for STS articles and letters.
Top of folk clubs page - folk dance clubs in Devon
Gittisham Folk Dance club - the original website
Sidmouth Folk Festival - the history since
How to run a folk dance club - experiences over 15 years
(most pages not yet completed)
Folk Dance Diary 2016 - highlights of a year of folk