问答题
(清华大学2006--2007学年春季学期期中考试试题)A football，meant to be thrown at 60 mi／h in sea--level air(ρ=1．22 kg／m
3
，μ=1．78E-5 N s／m
2
)is to be tested using a one—quarter(1／4)scale model in a water tunnel(ρ=998 kg／m
3
，μ=0．0010 N s／m
2
)．For dynamic similarity，what is the ratio of prototype force to model force?
【正确答案】正确答案：根据近似原则，若认为气体和液体是理想状态下的，则(Re)
p
=(Re)
m
【答案解析】