# How can i calculate the speed of an object in water

1. Sep 15, 2010

### DouglasEdward

I would like to know how fast an object will move through sea water.
Do you know if an accurate figure can be calculated? if so how?
I would like to know how fast 100 tonnes of steel -(streamlined )would fall through sea water.
I would also like to how how to calculate the figure for any object.

2. Sep 15, 2010

### Sakha

For a rough approximation you can just calculate gravity vs. buoyancy forces to determine the acceleration.

For a more accurate calculation you will need to take into account drag forces.

3. Sep 15, 2010

### QuantumPion

4. Sep 16, 2010

### DouglasEdward

where
Vt = terminal velocity,
m = mass of the falling object,
g = acceleration due to gravity,
Cd = drag coefficient,
ρ = density of the fluid through which the object is falling, and
A = projected area of the object.

i just want to chack i understnad the equation...

( 2xmass x accelaration gravity) divided by (density x area x drag coefficient)
= X square root of x = Vt

how accurate is this euquation considered to be; what is still missing.?

I put some very dense materials in with very low drag coefficients and i got figure up to 65 metre per second which seems a little fast

i got other things in and think that the figure is more realistic by making the drag coefficient 1 rather than 0.09.