In two inertial frame conclusion: 1.time interval is absolute t=t △t=△t 2. space separation is absolute x=x'+ut Vl=Vl,tiV,=vm,tiV for:△t=0so:△x=△ 3. the invariability of Newton's I aw F=ma=maF=F′F'=maIn two inertial frame a a    = conclusion: 1.time interval is absolute t=t t = t 2.space separation is absolute x = x  + ut x = x + ut = x + ut t = 0 x = x  3.the invariability of Newton’s law F = ma = ma for： so： F = F F = ma