PRINCIPLES OF GUNNERY. 
80 
dividing tlie mean pressure by the number of square inches in its sec¬ 
tional area. Thus 
P 
. , mean pressure P 
pressure per square inch = -- l— - = 
where d is the diameter of the bore in inches. 
Similarly, 
work done per square inch = 
total work done 
'7854c? 2 
PS 
'7854c? 2 
When a projectile is in motion, it is said to have energy — i.e., 
it is capable of doing work, or overcoming resistance. The amount 
of energy is measured by th q product of the voeight of the projectile into 
the height due to its velocity , and is expressed in the same units as those 
of work done. 
Thus, if IV be the weight of the projectile in lbs., h the height it 
would require in vacuo to attain a velocity v in feet per second, then the 
energy of the projectile is 
Wo* 
Wh = - -- ft. lbs. 
*9 
where h — 
2(7 
Now, if V be the muzzle velocity of the projectile, its energy at the 
W'V* 
muzzle of the gun is ----- ; and since the energy of the projectile is 
equivalent to the work done on it, 
win 
ZJL-=*PSi 
2g 
where E represents the energy at muzzle. 
It will therefore be seen that the energy of the projectile at the 
muzzle is equal to the work done by the pressure of the powder gas 
in the bore of the gun. 
Example. —Find the energy of the 10-in. M*L. gun at the muzzle, 
firing Palliser shell with a battering charge. Weight of shell = 400 lbs., 
muzzle velocity = 1361f;S. 
Energy at muzzle = 400 x C 1364 ) 3 f lb 
^ 2 x 82-19 
400 X ( 1364) 2 
2 x 32-19 x 2240 
ft. tons = 5160 ft. tons. 
i.e,, if a uniform resistance of 5160 tons were opposed to the shell, it 
would penetrate one foot before it was brought to rest; or if the resist¬ 
ance were 516 tons, it would penetrate 10 ft., and so on. 
In order to estimate the comparative power of guns for piercing’ 
iron plates, it is usual to express the energy of a projectile in terms of 
Work done 
per square 
inch. 
Energy. 
Energy 
per 'ne!i of 
circumfer¬ 
ence. 
* See “Treatise on Dynamics,”—XEotion of a Particle falling freely in vacuoj 
