One of my sons' favorite shows is Handy Manny on Disney Channel. In the show, Wilmer Valderrama's Manny has many helpful, talking tools. Whenever Manny has a job to do, he discusses it with his tools and they all get to work.
I imagine a scenario where Manny asks his hammer Pat to drive a nail into a board. The conversation goes something like this... ...
Manny: Please drive in that nail.
Pat: I can't
Manny: What do you mean?
Pat: Well, I learned about Newton's 3rd Law--for every action there is an equal and opposite reaction. When I hit the nail, the nail will hit me back with just as much force.
Manny: Go on... ...
Pat: Since the forces are equal and opposite, they will cancel. There's no reason to even bother--with equal and opposite forces, there's no chance the nail will move.
What's going on here? Is Newton's 3rd Law not really correct, or is there a problem with Pat's logic? What do you think?
I think that Newton's third law is not correct in this situation. Even though the forces are cancelling, there are still other forces acting upon the nail rather than just the hammer. An example is your arm. With the extra force coming down on the nail, the nail will drive into the wood without a problem.
ReplyDeleteThe forces aren't cancelling in this situation. If they were, the hammer would be correct in saying that the nail wouldn't move and Newton's 3rd Law would suffice for this. However, it doesn't because the forces that are acting are acting upon different objects.
ReplyDeleteFor this senerio i would just use basic knowledge and say that Newtons Law dosent apply to this. The nail will just use the force applied to it by the hammer and go into the wood.
ReplyDeleteI believe as well that Newton's third law isn't correct here and that there are many forces in this scenario. The forces do cancel out but I think there are other forces acting upon the hammer and nailn like gravity causing the hammer to push the nail into the board.
ReplyDeleteIf Newton's Laws are not always "correct," how do we know when they are applicable. What is it about this situation that makes Newton's Third Law not correct."
ReplyDeleteYou know it's applicable when the forces are acting on the same object and they cancel out. The situation makes Newton's Third Law incorrect because the forces aren't acting upon the same object and aren't canceling out.
ReplyDeleteThanks for all the comments this week!
ReplyDeleteOh, and by the way, the title of this post alludes to the punchline of the physics joke:
ReplyDelete"The moral of the story? Never teach a hammer only a little physics!"
HAHAHAHAAH yale physics great joke!
ReplyDelete