# The Naked Scientists Forum

### Author Topic: The weight is the pressure of liquid ?  (Read 1315 times)

#### fgt55

• Jr. Member
• Posts: 42
• LCF
##### The weight is the pressure of liquid ?
« on: 30/04/2012 16:02:49 »
Imagine a system like below. A helicoid can only turn around red axe. A cone has water in it. We put the cone like the drawing show below. We chose datas for have p1*s1 = p2*s2, it's possible because s1>s2 and p2>p1 and the angles of the cone and the helicoid can be chose like we want like the thickness of the helicoid.  The goal is to have torque = 0 for the helicoid, if mean radius are not the same need to have p1*s1*r1 = p2*s2*r2. Like that helicoid can turn freely without need energy. Is the weight of cone change because we suppress part of pressure of water ?

NB the relative position to cone from distance is always the same, the screw turn, the cone move up but is d = constante.

Edit: When the part of the helicoid is in water, this add weight to the cone but this weight can be ligher than the force cancel. The added weight can be smaller than the force cancel (or greater).
« Last Edit: 01/05/2012 09:36:55 by fgt55 »

#### fgt55

• Jr. Member
• Posts: 42
• LCF
##### Re: The weight is the pressure of liquid ?
« Reply #1 on: 02/05/2012 10:30:58 »
I give the sum of energy:

1/ We move down the water+cone this give m*g*h
2/ The helicoid turn without need energy
3/ We move up the water+cone we need m*g*h-Eh*sin()*Ph*d**g+g**Lh*Eh*Ph

Must to compare : -Eh*sin()*Ph*d**g+g**Lh*Eh*Ph = -sin()*d+Lh

sin()*d > Lh, I think it's possible so there is another problem... where ?

#### fgt55

• Jr. Member
• Posts: 42
• LCF
##### Re: The weight is the pressure of liquid ?
« Reply #2 on: 03/05/2012 17:13:57 »
someone see where it is false ? I think with a cone and another object (shape of the part of helicoid), if the sum of vertical forces is 0, we can put an object at bottom, this need energy E1, this increase the weight of cone but decrease weight because there is a part of surface less, in final we can have less weight. Move up the cone, move out the object recover energy E1.

Edit: more simple to study the drawing. We can replace water by small ball magnet, and the mass M replace by a big magnet. FS1 perpendiculary to the movement, FR give energy like that, where is the cancel force ?

And more, use only mechanical attraction like springs.
« Last Edit: 07/05/2012 21:59:51 by fgt55 »

#### The Naked Scientists Forum

##### Re: The weight is the pressure of liquid ?
« Reply #2 on: 03/05/2012 17:13:57 »