扭力，Torque

汽車商通常都會標榜「馬力」同「扭力」，Horsepower and Torque
上幾集講過角動量，Angular Momentum，L= r‧p，where
L= angular momentum
r=displacement between the object and the origin
p = linear momentum of the object
F= the force acting on the object
而扭力，或力矩，， change in momentum/t = F
而 r‧p=L，咁力矩就姐係角動量既改變既速率，其微分方程為

呢樣咁funny既野同好多可愛玩意都有關，例如陀螺......