物品重D 跌快?

If we neglect air resistance,
all of the object above the earth surface fall with the same gravitational acceleration and hence same time for it to fall from a certain height.This is by the basic motion equation of an object s=ut+0.5at^2. This equation is very simple so that you can look up from your physics book.

If we do not neglect the air resistance,
heavier object will fall faster than the same shape but different density object.It is because same air resistance force will act on them but different gravitational force will act on them, heavier object will have a larger force acting on since F=ma
mg-f=ma
a=g-f/m
From this simple equation, we can find out that in certain f, if m is higher, f/m will be smaller and hence a is larger.

I hope you can understand what i'm saying, if not please e-mail me.

你係邊度聽番嚟﹖定係你做過實驗呢，又或者係你直覺認為﹖
無論物體大小輕重，係相同重力下，下墜速度係一樣架，你有興趣，你可搜尋"加里略"睇睇。