How to detect if gameobject has been hit with enough force(speed) by another gameobject?

Hi, so I'm currently trying to implement an axe/tree cutting feature into my game, and so far I have been able to make the tree fall when my axe is touching it. My question is, how do I make the tree fall if I hit the tree with my axe fast enough/with enough force? For example, I don't want the tree to fall if I hit it with the axe lightly, but I want it to fall if I quickly hit it. Example of what I DON'T want to happen: https://gyazo.com/8cb0c460bc56e7fb6817caf3f7a139c8