# Moving a mass through water

1. Apr 17, 2014

### Stevethesub

I am planning building a sub. I am tring to find the amount of energy it takes to move it.
I think it should be equal to the energy needed to move the same volume of water.

For example say the sub had the volume of 10,000 cubis feet.

1. Is my assumptin right?

2. what formulas are ther for this?

3. Is more energy needed at deeper depth? Why?

If You have Ideas post thanks

2. Apr 17, 2014

### PhysicoRaj

Welcome to PF.

1.) No. Consider a case where you move a ball through air. Does it take the same energy it takes to move the same volume of air? No! The same way, the work to be done depends on it's mass and how far you want to move it.Work. But the force applied depends on the friction of the medium. Since viscosity of water is more than that of air, more force is needed. The viscous drag increases with velocity so more the speed, more force to apply. Ultimately the increased force means increased work to be done.

2.) work done=force applied*distance travelled. And the force applied includes the force you need to overcome the viscous drag.Work

3.)You will also have to consider one more important factor, http://en.wikipedia.org/wiki/Buoyancy

Principle of operation of sub

Last edited: Apr 17, 2014
3. Apr 17, 2014

### Chronos

Think of the case of an airplane. Aerodynamic principles must be taken into account to optimize design.

4. Apr 17, 2014

### Staff: Mentor

Homeade subs are extremely dangerous and a great way to die. Do you intend this to be flooded (and you wear scuba gear) or filled with air for you to breathe?

5. Apr 17, 2014

### PhysicoRaj

OMG I thought about somthn like this

6. Apr 20, 2014