“The Earth is Pulling on the Apple” 

“That certainly seems obvious enough. After all, the earth pulls on everything: me, you, stones, and people jumping out of windows. And the apple is so small as to be insignificant. But what if the apple were larger? What if the apple were one-quarter the size of the earth? Would the earth still be pulling the apple but the apple NOT pulling on the earth? What if the apple were bigger than the earth? Would it still be the earth pulling on the apple, but NOT the apple pulling on the earth?”