基本假设:冲击波是球面波,爆炸中心是该球面波的球心
数据:爆炸火球半径R的时序照片R(t)
量纲分析:
(1) 相关物理量:能量E,时间t,介质密度D,火球半径R
(2) 基本单位:
(a) L 长度量纲
(b) T 时间量纲
(c) M 质量量纲
(3) 量纲列表:
(a) [R] = L
(b) [E] = ML^2/T^2
(c) [t] = T
(d) [D] = M/L^3
假设:
[R] = [E]^x [D]^y [t]^z
由量纲列表知:
L = M^{x+y} L^{2x-3y} T^{-2x+z}
比较等式两边指数可得方程组:
x + y = 0
2x – 3y = 1
z – 2x = 0
解之可得:
x = 1/5, y = -1/5, z = 2/5
代入假设可得
R = C * E^{1/5} D^{-1/5} t^{2/5}
其中C是待定常数,作为数量级估计,暂作1. 为求所释放能量,由上式求解E:
E = R^5 D / t^2
根据照片数据:
R(t = 0.006s) = 80m
并取空气密度D = 1.2kg/m^3; 1克TNT = 4e+10 ergs,可得:
E ~25000 吨TNT
参考:
[1] Taylor G, The Formation of a Blast Wave by a Very Intense Explosion: I. Theoretical Discussion. Proc. R. Soc. Lond. A201, 159–174 (http://www-astro.physics.ox.ac.uk/~garret/teaching/taylor1.pdf)
[2] Taylor G, The Formation of a Blast Wave by a Very Intense Explosion. II. The Atomic Explosion of 1945. Proc. R. Soc. Lond. A201 175–186 (http://www-astro.physics.ox.ac.uk/~garret/teaching/taylor2.pdf)