Here are the usual three classes of levers:

enter image description here Source: http://mrtremblaycambridge.weebly.com/p15-turn/ing-on-a-pivot.html

Does the fulcrum of a 2nd or 3rd class lever have to be at the end? If so why? Why not have just a little bit more board beyond it? Why right at the end?


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    $\begingroup$ Is the fulcrum of your wheelbarrow lever at the absolute end? $\endgroup$ – DJohnM Jul 14 '17 at 3:57
  • $\begingroup$ It's like that because it's been made like that. One to act as a speed multiplier (3rd class, as mechanical advantage is always <1), and one to act as a force multiplier (2nd class, as mechanical advantage is always >1). $\endgroup$ – Wrichik Basu Jul 14 '17 at 4:56
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    $\begingroup$ I'm a little unclear on what the question here is - the 2nd and 3rd class are defined by the load and the applied force being on the same side of the fulcrum. Whether the physical implementation of such a lever extends beyond the fulcrum to the other side makes no difference to this physical situation. What exactly is the question? $\endgroup$ – ACuriousMind Jul 14 '17 at 9:51
  • $\begingroup$ Side note: the link to the source does not appear to work. $\endgroup$ – ZeroTheHero Jul 14 '17 at 11:58
  • $\begingroup$ @ACuriousMind in some of the sources I googled, they seem to suggest that the fulcrum must be at the end. I am asking is it required to be at the end? Or is it just that the two forces must be on the same side? $\endgroup$ – Stan Shunpike Jul 15 '17 at 1:57

Speaking practically, it would make no difference the Fulcrum need not to be at the far end of the machine, to be a Second Class or Third Class Lever, as long as the Load is situated in between and Effort at the other end, that is the Effort Arm (distance between Fulcrum and Effort) is longer than the Load Arm (distance between Load and Effort) the Lever is a Second Class or if the effort is in between and load at the other end, then a Third Class Lever, in case any extra part is present beyond the Fulcrum in a second class or third class lever, that extra part is excluded or included in the Lever and does not make any difference.

Because, if we were to make calculations about certain quantities like Mechanical Advantage, Velocity Ratio, Efficiency of the lever, we would make calculations from the point at which the Fulcrum is located. Let us consider, the Fulcrum of a Second Class Lever is not situated at the far end but is somewhat away from the end. The Load is present in between. Now if we were to calculate the Mechanical Advantage of the Lever :-

Mechanical Advantage = Effort Arm/Load Arm------------(1)

Since it is proven both mathematically and experimentally that Mechanical Advantage (M.A.) of a Lever is equal to the ratio of its Effort Arm and Load Arm, we would try not to go much deep into the derivation of the equation. Now let us say that there is an extra part (F') beyond the fulcrum and we were to include that in making calculations of the M.A. of the Lever along with the presence of Fulcrum(F). So now the new Effort Arm after including the extra part (F') would be F'E and new Load Arm would be F'L.

Calculating the new M.A. with F'E and F'L :-

M.A. = F'E/F'L

In this case the extra part F' would simply become the new Fulcrum of the Lever, but since Mechanical Advantage is a ratio of the Effort Arm and the Load Arm and the common factor being the extra part (F') which we are considering in the Lever, the ratio of that Lever would come out the same and hence it will not affect its working. If we were to exclude the extra part F' from the Lever again we would get the original M.A. ratio and the working of Lever would be the same. Therefore we conclude that the presence of any extra board beyond the original fulcrum would not make any difference in the working of Lever and can either be included or excluded in making calculations about the Lever.A simple diagram below representing the explanation.


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