BY NEWTON'S FIRST LAW
a body remains at rest or moves along a straight ling with uniform speed if there is no net force actiong on it.
同埋每一物件都有inertia(慣性)
mass愈大 inertia愈大
未開車時,你同車都係at rest,開車ge時後,你會remain at rest by inertia
so 你會。身體會向後傾
到剎車o個時,你本來同車一齊accelerate or move in uniform speed 緊,又係因為有inertia,你會moves along a straight ling ,so你身體會向前傾。