# Lift force?

1. Sep 22, 2015

### yilbaris

We all know the lift force in case 1, what about case 2 ?

2. Sep 22, 2015

### Orodruin

Staff Emeritus
Note that there is also a force from the liquid pushing down on the additional wings you put in ...

3. Sep 22, 2015

### MrAnchovy

Buoyant force depends only on the amount of water displaced, not the shape of the object displacing it.

4. Sep 22, 2015

### SteamKing

Staff Emeritus
If by "lift force", you actually mean "buoyancy", this can be calculated for case 2, although it is slightly more complicated than case 1.

Remember Archimedes' Principle:

https://en.wikipedia.org/wiki/Archimedes'_principle

Note: in technical use, "lift force" is usually reserved for a force which is created by a dynamic situation, like the lift generated by an airplane's wings when flying.
OTOH, "buoyancy" usually refers to a force created by a static situation, like the displacement of fluid by a floating object.

5. Sep 23, 2015

### yilbaris

?????????? To calculate the resultant force is possible, but i wonder distribution of force. ??????????

6. Sep 23, 2015

### MrAnchovy

Every point on the submerged surface of the object feels a normal force proportional to the pressure at that depth $\rho g h$

Last edited: Sep 23, 2015
7. Sep 23, 2015

### Orodruin

Staff Emeritus
A force can never equal a pressure, the dimensions are different. An area element is subjected to a normal force equal to the pressure multiplied by the area

8. Sep 23, 2015

### yilbaris

Thank you all.

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9. Sep 23, 2015

### MrAnchovy

I wanted to steer clear of elemental areas for the sake of clarity but I take your point; I have amended 'equal' to 'proportional'.