Stretching out shapes from an anchor?

Hi, im having a little trouble grasping a concept which I think is simple enough.

assume there’s a small rectangle. I grab left corner of it, and stretch it out with an elastic rubber effect of some sort, and then another corner gets yanked. and so on.

i wonder if this sort of thing can be done in AS opposed to timeline tweening?

this is an example i’ve seen done over and over.

what im trying to achieve is: there’s a small half circle(think of it as a hill) on the stage and i want it to lean and grow left or right by the highest point of the circle.

any ideas?