1247 
ABSTRACT 
When a shock collides with a structure, the resulting 
damage depends upon the duration of the blow as well as upon 
the initial pressure due to it. In spite of this commonly 
appreciated fact no theoretical attempt (going beyond acoustic 
theory) has been made to find the complete pressure-time curve 
at a reflecting surface xcept in one calculation by Chandrasekhar. 
He treated the case of normal reflection from a rigid surface 
in air and obtained his results by a numerical method.-. In 
the present report, too, normal reflection from a rigid 
surface is considered, but the numerical method is replaced 
by an analytical one and the work is extended to pressure- 
ime curves in other gases and in water. Now the pressure-=- 
time curve at a wall can be roughly described by three characteris- 
tics, namely: (1) its peak pressure, (2) its curvature, and (3) 
its duration. It is well-known that in all media the initial 
overpressure caused by normal reflection at a rigid wall ex- 
ceeds the acoustic value (which is double the overpressure in 
the incident pulse). In this report it is found that the 
correct theoretical pressure-time curves at the wall are, in 
typical fluids, concave upward more strongly than their acoustic 
approximations. With respect to the third of the above prop- 
erties, however, gases and water are here found to behave 
differently. In gases the blow is prolonged and the impulse 
delivered to a rigid wall exceeds the value predicted by 
acoustic theory. In water, on the other hand, the blow is 
shorter and the impulse is less than one would expect from 
-[= 
