Sometimes when going round a corner, a double-decker bus appears to be about to keel over. What would the angle from the vertical have to be before this would occur?

According to Martin Davies of Welshpool (Sept 6) the bus would keel over “when the top right hand corner is further left than the bottom left-hand corner or the top left-hand corner is further right than the bottom right-hand corner. This would mean an angle of displacement from the vertical of more than 45 degrees.” This is wrong on a number of counts.

It assumes that the bus is of uniform density throughout so that the centre of gravity would be at the intersection of the two diagonals from top left to bottom right and top right to bottom left. This is not the case as, for example, the engine of the bus is located low in the bus, thus lowering the centre of gravity. The position of the centre of gravity would also be affected by the number of passengers, their mass and their distribution in the bus.

Even if I was correct, the critical angle of displacement would not be more than 45 degrees, as claimed by Mr Davies, as the bus is of rectangular cross-section. For the angle to be 45 degrees the bus would have to be of square section (and be of uniform density). Neither the answer given by Mr Davies nor that of Mr Reeves (Sept 6) addresses the issue of the bus going round a corner when other forces are involved in addition to gravity.

The photograph shows a bus undergoing a static tilt test showing that the top right-hand corner is clearly much further left than the bottom left-hand corner and the bus has not keeled over. The top deck has been loaded with sandbags to represent the weight of passengers.

J. W. Lewis, Broxbourne, Herts

Recently a dental consultant at Eastman Dental Hospital, London, told me that “many dentists now call themselves doctor”. Is this so?

The title has been in general usage among dentists for a few years, after a campaign entitled “call me doctor”.

With the advent of free movement within the European Community, dentists from other EU countries were free to work here. Most other European countries confer the title of doctor on their dentists, recognising the parity of training, and some UK dentists did not wish to appear less qualified than their EU colleagues.

The title of “doctor” used by physicians is purely a courtesy title, used and generally accepted in the UK. Physicians do not possess a higher doctorate such as PhD or DPhil and so the title is not formal. Indeed, when “doctors” become surgeons, they drop the title and become “Mr” as a sign of superiority. So, as long as your dentist does not purport to be a medical practitioner, he or she is perfectly entitled to use the title “doctor”.

Jeremy A. Woodcock, Chalfont St Giles, Bucks

Owing to an editing error in last week’s answer by Paul Courtenay, the chairman of the Churchill Centre, UK, to the question about Sir Winston Churchill’s uniforms, we omitted the fact that the 5th (Cinque Ports) Battalion, of which Churchill was Honorary Colonel, was an integral unit of The Royal Sussex Regiment. Our apologies.

Questions

In British courts an alternative oath is available to witnesses who object to swearing “by almighty God”. What is the position in the US and does the oath there (standard or alternative) differ between states?

Roy Hyde, Cheltenham, Glos

How many standard games of Su Doku is it possible to set? And what are the factors that make any particular game easy, mild or fiendish?

Veryan Herbert, Sudbury, Suffolk

Postcodes are made up of two parts, eg, E98 1TT, and in the second part of the code the letters C, I, K, M, O and V are never used. What is the reason for this?

C. Byrne, Oxford

What is the origin of the letters around the dressage ring? They don’t seem to have any logic.

Jeremy Hills, Tonbridge, Kent

E-mail your questions and answers to q&a@thetimes.co.uk, fax them to 020-7782 5870 or write to Questions Answered, The Times, 1 Pennington Street, London E98 1TT. Please include your address and daytime telephone number.