Answer to Question #94491 in Classical Mechanics for Tyler

Question

Having some trouble with class 2 levers... We are working on a simple machines curriculum for elementary school use, and a colleague believes that a springboard is a class 2 lever. I think that it is not (at least, not -just-) because the board bends under downward effort applied to it, and then the flexing force of the board material is where the upward effort comes from... do levers, in their most basic sense, need to be rigid? Can you help clear this up for me?

Answer 1

Yes, usually when we speak about levers, it is implied that they are rigid bodies, at least theoretically. On the other hand, can you claim that a wooden or metal rod (beam) used as "strict" levers do not bend? For instance, a stapler (class 3), or a wheelbarrow (class 2) or pliers (class 1) also bend under load, but the distance between some point in the normal state and the same point in bend state is insignificant. The same reasoning can be applied to a springboard, since all effort is applied very close to the point where the springs are attached to the board, and the bending is no so significant. Not to confuse students (unless they design springboards), in my humble opinion, that springboard can be considered as class 2:

[http://springboardsandmore.com/products/maxiflex-16-foot-cheeseboard/]

and class 3 lever most likely if it is like this:

[https://www.continentalsports.co.uk/springboard-junior-powerboard]

Because, fairly speaking, everything bends in our imperfect world...