Help WIth Theoretical Mechanical Advantage.?

Question

Please help! I am learning about lever systems...the question is
What is the theoretical mechanical advantage for a third class lever?
I am looking for a SPECIFIC number, not just an explanation.


Here is a picture of the third type of lever incase you don't know what I am talking about-

http://www.sciencebyjones.com/third_class_levers.htm

ps. My teacher told us that the theoretical mechanical advantage for type 1 is '1' and for type 2 it is '2'...and now we had to figure out what it is for 3 but she never taught us how!!

Answer 1

I think you must have misunderstood. Class 1 levers can have an advantage of 1/2, or 8, or 13.7. Class 2 levers always have advantage greater than 1, maybe 1.5, maybe 4.7. Class 3 levers have advantage always less than 1. The actual advantage about a specific lever depends on the dimensions.

The webpage http://en.wikipedia.org/wiki/Mechanical_advantage says
Ideal Mechanical Advantage = DE/DR
where DE equals the effort distance and DR equals the resistance distance.

Effort distance means the distance the applied force moves. Resitance distance means the distance the load moves.

Looking at the figure you included, lets guess the load is 2x as far from the fulcrum as the effort. If the effort gets the lever to rotate through a curve 10 mm long, the load will go 20 mm. So the advantage is
Ideal Mechanical Advantage = DE/DR = 10 mm/20mm = 1/2

But that's just an example. If you move the effort closer to the fulcrum, the advantage could be 1/3.