uniform circular motion

圖片參考：http://imgcld.yimg.com/8/n/HA00140412/o/701007240107613873371840.jpg

The reason for tilting in wards is to allow the normal reaction by the ground to exert a torque about the CG to balance the torque by friction. This keeps the motorcycle in equilibrium and avoids overturning. From the equation (tan phi = v^2/gr), we see that the angle increases with speed. Qualitatively, if the speed increases, the magnitude of friction will increase as to provide a larger centripetal force required for turning. The increase in friction causes an increase in torque due to the friction about CG. This increase in torque must be balanced by the additional torque due to reaction to avoid overturning. Since reaction equals mg, the only way to increase the moment is to increase the moment arm about CG, i.e. the dtriver leans inwards.

2010-07-24 21:09:20 補充：
This keeps the motorcycle in ROTATIONAL equilibrium and avoids overturning.