Moving a mass through water

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In summary, the conversation discusses planning to build a sub and finding the amount of energy needed to move it. The assumption that the energy needed is equal to the energy needed to move the same volume of water is incorrect, as the work to be done depends on the mass and distance traveled, and the force applied depends on the friction of the medium. The increased force needed to overcome the viscous drag of water ultimately means increased work to be done. Formulas for calculating work done and the force needed are suggested, and the importance of considering buoyancy and aerodynamic principles in sub design is mentioned. The dangers of homemade subs are also pointed out.
  • #1
Stevethesub
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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
 
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  • #2
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

And these might help you:Archimedes principle applied to subs

Principle of operation of sub
 
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  • #3
Think of the case of an airplane. Aerodynamic principles must be taken into account to optimize design.
 
  • #4
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
Stevethesub said:
For example say the sub had the volume of 10,000 cubis feet

OMG :bugeye: I thought about somthn like this

0.jpg
 
  • #6

1. How does the density of the mass affect its movement through water?

The density of an object greatly affects its movement through water. Objects with a higher density will sink in water, while objects with a lower density will float. This is due to the buoyancy force acting on the object, which is determined by the density of the object compared to the density of the water.

2. What factors affect the resistance of water to the movement of a mass?

The resistance of water to the movement of a mass is affected by several factors, including the mass and shape of the object, the speed of the object, and the viscosity of the water. These factors impact the drag force acting on the object, which is the force that opposes the movement of the object through water.

3. How does the shape of an object affect its movement through water?

The shape of an object greatly affects its movement through water. Objects with a streamlined shape, such as a boat or a fish, experience less resistance and are able to move through water more efficiently. On the other hand, objects with an irregular shape will experience more resistance and will move through water at a slower pace.

4. What is the difference between laminar and turbulent flow in water?

Laminar flow is a smooth, orderly flow of water, where the water particles move in parallel layers. This type of flow occurs at low speeds and is less resistant. Turbulent flow, on the other hand, is a chaotic flow of water, where the water particles move in different directions and at different speeds. This type of flow occurs at higher speeds and is more resistant.

5. How does the viscosity of water affect the movement of a mass through it?

The viscosity of water, which is its resistance to flow, greatly affects the movement of a mass through it. Water with a higher viscosity will offer more resistance to the movement of a mass, making it more difficult to move through. This is why swimming in honey, which has a higher viscosity than water, is much more difficult than swimming in water.

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