2 APPLIED MECHANICS 
3. The C. G. S. System of Units.—This is the system of units 
recommended, for scientific purposes, by a committee of the British 
Association. The centimetre is the unit of length, the gramme is the 
unit of mass, and the second is the unit of time. 
- The unit of area is the square centimetre. 
The unit of volume is the cubic centimetre. 
The unit of velocity is a velocity of a centimetre per second. 
The unit of momentum is the momentum of a gramme moving with 
a velocity of a centimetre per second. 
The unit of force is that force which generates a unit of momentum 
in a second, and is therefore that force which, acting on a gramme for 
one second, generates a velocity of a centimetre per second. This unit 
of force is called the dye. 
The unit of work is the work done by a force of a dyne acting through 
a distance of a centimetre. This unit of work is called the erg. 
4. Equivalents of Ordinary British and C. G. 8. Units. 
1 foot = 30°479 centimetres. 
1 centimetre = 0°0328 foot. 
1 square inch=6°451 square centimetres. 
1 square foot = 928-997 square centimetres. 
1 square centimetre = 0°155 square inch = 0:001076 square foot. 
1 cubic inch = 16-386 cubic centimetres. 
1 cubic foot = 28315°3 cubic centimetres. 
1 cubic centimetre = 0°061027 cubic inch = 0:00003532 cubic foot. 
1 lb. avoirdupois = 453°593 grammes. 
1 gramme = 0°0022 Ib. avoirdupois. 
1 foot per second = 30°479 centimetres per second. 
1 mile per hour = 44°703 centimetres per second. 
1 centimetre per second = 0°0328 foot per second = 0:02237 mile 
per hour. 
1 Ib. per cubic foot = 0°01602 grammes per cubic centimetre. 
1 gramme per cubic centimetre = 62°4245 lbs. per cubic foot. 
Accelerating effect of gravity =32°2 feet per second Sg second — 
= 981:44 centimetres per second per second. 
In the equivalents below g is taken = 981 centimetres per second 
per second. 
1 lb. avoirdupois = 444974 dynes. 
1 gramme = 981 dynes. 
1 foot-pound = 13562570 ergs. 
1 kilogrammetre = 98100000 ergs. 
1 lb. per square inch= 68974 dynes per square centimetre. 
_ 1 Ib. per square foot = 478-98 dynes per square centimetre. 
‘1 kilogramme per square centimetre = 981000 dynes. per square 
centimetre. 
5. = ei. 2 asaam — 
2 
+ax+b=0, then #= r5e sven! — 46 
The roots of an equation are the values of x which satisfy the e cin 
If a and B are the roots of the equation ee Ge. b=0, then | e+P= —a, 
and By 
