when a leaf falls from a tree, which exerts force, the leaf or the tree?

Question

anonymous · Answer

I think its the earth, it exerts gravitational force.

anonymous · Answer

there are there external forces working on the leaf. earth's gravitational force, drag force caused by air, and an extremely small gravitational force from the tree which can be ignored.

anonymous · Answer

*three   sorry for mistyping

anonymous · Answer

$$F = (GM _{leaf}M _{earth})/(R_{earth-leaf}^{2})$$

anonymous · Answer

$$F = (GM _{tree}M _{earth})/(R_{tree-leaf}^{2})$$

anonymous · Answer

i don't know how to count the drag force caused by air

turingtest · Answer

Though everything azzam said is true, the answer I believe you are looking for is the "the leaf". This is because the leaf, as a result of the earth's gravitational field, has a weight to it and therefor is exerting a force on the tree. The earth itself exerts no force other than that due to you standing on it. The force of gravity, as can be seen in azzam's equation above, is a result of the interaction of TWO masses (that of the leaf and the earth in this case).

However I take issue with this question, because it says "when a leaf falls from a tree". Before it falls from the tree there is the tension force of the tree branch in balance with the gravitational pull of the leaf, and when the leaf falls it cannot be exerting a force on the tree. It is the force of the leaf on the tree that CAUSES the leaf to fall. So I would say the phrasing of this question is poor, though I stand by my answer as the one they are looking for.

anonymous · Answer

Although someone from a biology group may provide information about how and when a leaf is forced to leave the tree, they sometimes don't just drop.

anonymous · Answer

i've misunderstood the question lol :-)