What Is the Difference Between First, Second & Third Class Levers?

By Walter Unglaub

The difference between first, second and third class levers lies in the relative positioning of three items. Find out about the difference between first, second and third class levers with help from an experienced physics professional in this free video clip.

Transcript

Hello, my name is Walter Unglaub, and this is what is the difference between first, second and third class levers. The difference lies in the relative positioning of three items. Those would be the effort, which is the force that is applied by the person or the external force, the resistance, which is typically the mass that you're trying to move and the fulcrum, which is the pivot point for the lever. So, in the case of first class levers, we have the fulcrum in between the effort and the resistance. So if you imagine a block of mass m, that is the resistance due to the fact that there's a gravitational force that is exerting this weight. The effort then will be on the other side of the fulcrum, and if you push down on this end, then the motion will be in this direction, and will cause the mass to rise. For a second class level, there's a different ordering of the effort, fulcrum and resistance. For second class, the fulcrum will be at the end of the lever. Now this would be akin to a wheel barrow for example, where you have a mass that exerts a resistance in the downward direction, but in this class instead of pushing down, the effort will be in the up direction. So, this effort will induce motion in this direction, causing the mass to be lifted off of this fulcrum, off of this pivot point. Finally, for the third class lever, we have the fulcrum at one end, and now the ordering of the effort and the resistance will change. So, we're going to have some mass on the other side of the lever, and that is the source of the resistance, but now the effort will be in between the resistance and the fulcrum. So, the motion again will be in the upward direction, except instead of a wheelbarrow, this is a more of some sort of a construction equipment where you have some shovel and it has some mass, and you're pulling up and pivoting off of this fulcrum point. So, we see that between the first, second and third class levers, the ordering is effort, fulcrum, resistance, then effort, resistance, fulcrum, and finally resistance, effort, fulcrum, in the way that I drew these pictures. My name is Walter Unglaub, and this is what is the difference between first, second and third class levers.

About the Author

Walter Unglaub graduated from the Colorado School of Mines with a B.S. in Engineering Physics and a M.S. Applied Physics.