This is the section on which we have a static rod like we did in statics

only this time is is some what submerged in a liquid!!!

Look at the Diagram below, redraw the diagram and label the the forces that act upon the system below.

The green line is a string supporting one end of a wooden beam, the beam floats in water and has a mass of W and a length L

So how did you get on ?

Can you break these forces into manageable units ?

Notice that not all the rod is under water!

What implications will this have to balance the forcess

What were the 3 ideas of statics ?

Forces Up = Forces Down

W = B + T

Forces Left = Forces Right

There are no forces left or right

Forces Clockwise = Forces Anti-Clockwise

Like we said in statics we can take the moments about any point. The best point to take would leave us with the fewest calculations. That would be the point in the liquid where the weight of the submerged part and the buoyancy act through.

Okay so do the Questions


Up = Down

B = (1/3W) / s

F + (1/3W) / s = W

Moments about the submerged CoG

2/3W (3) = (5) F

F = 2/5 W

sub back in to 1

2/5 W + (1/3W) / s = W

solve for s

s = 5/9