Cylinder r Head 汽缸盖 ; 缸头
shower r head 淋浴喷头 ; 莲蓬头 ; 淋浴头
cutter r head 刀盘体
laser r head 激光头
stair r head 楼梯顶口
cover r head 顶封头
The head of the C.R.U.,Phil Jones, temporarily left his position.
VOA: special.2010.01.19
The most important result from last time was that if you took this r, and you took two derivatives of this to find the acceleration, d^2 r over dt^2, try to do this in your head.
上节课最重要的结论,就是如果你把 r 写成这样,对 r 求两次导就能得到加速度,d^2 r / dt^2,心算一下
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