From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Page from a document explaining the principles of motion and the concept of 'Effective Forces' in dynamics.
| Identifier | WestWitteringFiles\M\2October1924-December1924\ Scan16 | |
| Date | 1st October 1924 guessed | |
| -2- Contd. (a) The motion of the centre of mass is precisely the same as it would be if the mass of the whole body were collected into a particle at the centre of mass and all the forces applied to the body were transferred to this particle without alteration of magnitude or direction, irrespective of any rotational motion which the actual body may have under the action of the forces. (b) The rotational motion of the body about its centre of mass is precisely the same as if the centre of mass were held at rest (or constrained to any other motion than the actual) and the body acted upon by the same system of forces, irrespective of such translational motion as the actual body may have under the action of the forces. From this it will be clear that if we know the linear motion of the centre of mass of a con. rod, and its angular motion about the axis through the centre of mass, parallel to the engine axis, we can say that a certain linear force (or simple system of forces) of known magnitude, viz. a simple force (or system) which is the equivalent of the system acting upon the imaginary particle in (a) above, are acting upon the rod at the centre of mass, together with a couple of known magnitude, viz. equal to the resultant moment of the system of forces about the centre of mass in (b) above, acting upon the rod transversely. Such equivalent forces, here inclusive of the couple, are what are known as the "Effective Forces". They may not be those actually applied, but are a simple set of forces which, acting freely on the body in question, would produce in it the actual motion to which it is constrained, and they form therefore an equivalent system to the actual forces. This notion of the "Effective Forces" is a very useful one in dynamics generally, and also in particular in this case, | ||