DO MOVING TRAINS REST ON THE RAILS?

King Country Chronicle, Volume VI, Issue 433, 24 January 1912, Page 2

DO MOVING TRAINS REST ON THE RAILS?

An enquirer (says "Popular Science Sittings,) has asked a curious question calling for a somewhat lengthy answer. The question runs : Does a train, while moving on an absolutely level track, a nd at a very high rate of speed, have any less pressure on the rails than when at rest ? We have it reckoned out by a learned professor that a train running around the entire surface of the earth at the rate of 4.91 miles per minute would have no pressure on the rails, but we think that ho has taken into consideration the circular shape of the earth's surface, and calculates that the centrifugal (a tendency to recede from the centre) force would throw it away from the centre and cause:it to have no pressure on the rails at the speed named. What we want to know is that if it wers possible to build a railway line of equal length, absolutely level, regardless of the earth's surface, as level as the lines of- a ray of light, would a train running at a high speed have, any less pressure on the rails than when at rest ? If it does haTe less pressure, what law causes it to ' have less pressure ? What force causes it to rise ? There is no reason, argues our correspondent, why a train running at any rate of speed should reduce its pressure, upon the rails if the earth's surface is considered as a plane and centrifugal force is neglected while gravity remains constant, unless, of course, it is equipped with aeroplanes at such an angle of attack, as to use wind pressure to decrease its rail pressure. It is easy to calculate the speed at which centrifugal force will theoretically balance the attraction of gravity, but it is demonstrably untrue that there is any such effect in practice, for a combination' of reasons too long to be discussed here.

It may be shown that the driving wheels of a locomotive press less on the rail for a part of their revolution at high speeds, and even leave it altogether, but this is due to inadequate balance of the thrust of the reciprocating parts at such speed, and has no connection with the principle of the problem advanced. It is imaginable also that' a train might ascend a, gradient on a trestle, for instance, at such a speed as to leap off at the end and be carried some distance by the ballistic (spring) effect of its momentum (impetus) from which it might be argued that reduction of rail pressure by speed is analogous, or similar, but this again is outside the limits laid down in the question. It appears to us that with a sufficiently high speed the pressure on the rails will be reduced towards vanishing point. Such pressure may be represented as a force compounded of the acceleration of gravity (the rate at which a body falls freely) and the horizontal speed of the train ; and as the last-named factor increases the vertical component of the force will lose in relative importance.