Fulcrum question

handirifle · Apr 17, 2012

I am thinking of making a manual press, for a non tractor related idea.

My thinking is that if I use a 48" long lever, with the pivot point within 1" from the end and pressure point about 8" from same end, leaving 40" of actual lever, and with me weighing 170lbs, how much pressure would that create? It will be pressing on an object 3/8" in diameter (.375") or at least very close to that.

SPYDERLK · Apr 17, 2012

47/7 x 170 ~ 1141# ... more with your pockets loaded

strum456 · Apr 17, 2012

That would be a 6:1 ratio. 6x170 is 1020 lbs.

handirifle · Apr 18, 2012

SPYDERLK said:
47/7 x 170 ~ 1141# ... more with your pockets loaded

:laughing: Every little bit helps.

OK, thanks guys, that was how I was figuring it, but wasn't sure if i was missing something.

Den1952 · Apr 18, 2012

did I read that right? your force point is 7" from the fulcrum? with one inch on the load side of the fulcrum is then a 7:1 ratio. I thought at first you meant to apply force 8 inches from the far end of of the lever, which would have been a 39:1 ratio.

strum456 · Apr 18, 2012

Please help with my second class lever dilemma.

Lets say it is 1' from the load to the fulcrum and 4' from the load to the effort.

That would be a 1:4 ratio, correct? If the load was 100lbs, the effort would be 25.

Now the load is in the middle. Say it is 2' to the fulcrum and 2' to the effort.
This would be a 1:1 ratio, correct? If the load was 100lbs, the effort would be 100 at a 1:1 ratio. BUT, the fulcrum is obviously supporting HALF the weight, so common sense tells me the answer is 50lbs.

What am I not understanding here? :confused2:

EDIT:
DARN....I tried to draw a picture with dashes, but it takes all the spaces out. I hope you can visualize without it.

schmism · Apr 18, 2012

google around a bit.

if you dont know how to draw and analyze the free body diagram yourself, theres likely someone who had made a simple converter for you for most simple cases.

for instance

Simple Lever Calculator Case #1 - Engineers Edge Engineering Calculators

in the above case converter

the weight that can be lifted up on the left end of the piviot is the same amount of force that can be applied downward on the right side of the piviot.

put another way, useing the above calculator, if you calculate you can lift 1000 lbs 1" away from the pivot on the left end, you could instead, squish something down with a 1000 lbs of force 1" to the right of the piviot.

strum456 · Apr 18, 2012

Thank you....the convertor confirmed what I was thinking.

I am a teacher. Trying to EXPLAIN this is a bit harder than just doing it. My problem is the formula I am following doesn't work when the weight is way in exactly in the middle. In other words, mathematically, my ratio is 1:1, but in reality it is 1:2.

LD1 · Apr 18, 2012

strum456 said:
Now the load is in the middle. Say it is 2' to the fulcrum and 2' to the effort.
This would be a 1:1 ratio, correct? If the load was 100lbs, the effort would be 100 at a 1:1 ratio. BUT, the fulcrum is obviously supporting HALF the weight, so common sense tells me the answer is 50lbs.

What am I not understanding here? :confused2:

EDIT:
DARN....I tried to draw a picture with dashes, but it takes all the spaces out. I hope you can visualize without it.

that is still a 1:2 ratio.

The ratio is (distance from fulcrum to load)

distance from fulcrum to force)

So if what you are saying is like this....

_______________________________
^..........................L..............................F

Where:
^=fulcrum
L=load
F=force

There is 2' between the fulcrum and the load and 4' between the fulcrum and force....1:2

strum456 · Apr 18, 2012

LD1 said:
that is still a 1:2 ratio.

The ratio is (distance from fulcrum to load)distance from fulcrum to force)

So if what you are saying is like this....

_______________________________
^..........................L..............................F

Where:
^=fulcrum
L=load
F=force

There is 2' between the fulcrum and the load and 4' between the fulcrum and force....1:2

I think I understand now. With 1st class levers, I would always just compare one side of the fulcrum to the other to get the ratio. With 2nd class levers, I was trying to compare the distance from the Fulcrum to the Load with the distance from the Load to the Effort. As far as I can tell, this will give the same answer as your method, except when the load is right in the middle. Your method works for all classes of levers as far as I understand. I will have to switch.

Thank you Sir!