重力&重力加速度

9.8 ms^-2 只係地球表面的strength of g is a function of height g=GMe/Re^2

質量係1kg<--  質量係mass=rest energy of a body >> constant for an object with low velocity relative to light speed, independent of gravitational field.

Weight=force=mass * g  <-- dependent of the strength of gravitational field

definition: ds/dt=v, d^2s/dt^2=dv/dt=a

for constant acceleration:a=V-U/T2-T1

setting T1=0, a=(v-u)/tv=u+at