How does a submarine (sub) work?
This sub's driver is called Sue Marra. Her partner is diving outside the sub. His name is Jacques Cousteau, the world famous deep sea explorer. If a shark gets too close to Jacques, he will be bop it on the nose!
What forces cause a submarine to move?
There are two forces that make an object move up and down in water: gravity and upthrust. (The Earth's gravity gives objects weight and pulls them down.)
Gravity gives a submarine weight and pulls down on a submarine.
There are two forces that make an object move up and down in water: gravity and upthrust. (The Earth's gravity gives objects weight and pulls them down.)
Gravity gives a submarine weight and pulls down on a submarine.
Upthrust gives you a push!
Upthrust is a pushing force so it is the opposite of gravity. Upthrust happens when an object displaces water. To displace means to move out of the way.
If you push a pencil down under the water and let it go, it pops back to the surface. Upthrust is the force that pushes the pencil back to the surface.
The strength of the upthrust depends on how much water has been moved out of the way. The strength of the upthrust is the weight of the amount of water that has been displaced.
Upthrust is a pushing force so it is the opposite of gravity. Upthrust happens when an object displaces water. To displace means to move out of the way.
If you push a pencil down under the water and let it go, it pops back to the surface. Upthrust is the force that pushes the pencil back to the surface.
The strength of the upthrust depends on how much water has been moved out of the way. The strength of the upthrust is the weight of the amount of water that has been displaced.
Submarines can change their weight
Subs can control their weight to be more or less or the same as the upthrust. For any object to start to move, one force needs to be stronger than the opposite force. A submarine moves if either gravity or upthrust is stronger.
A submarine will:
A submarine will:
- Sink if it weighs more than the amount of water it has displaced (because gravity is stronger than upthrust).
- Rise up if it weighs less than the amount of water it has displaced (because upthrust is stronger than gravity).
- Float/stay still if it weighs exactly the same as the amount of water it has displaced (because gravity and upthrust are equal).
How does a sub change its weight?
A sub dives/sinks by increasing its weight. It does this by letting water into its tanks while letting air out of the top of the tanks. Water weighs more than air so the more water that comes in the more the sub weighs. The force of gravity becomes greater than the upthrust and the submarine moves downwards.
It rises to the surface by blowing out the water. The less water in the tanks, the less the sub weighs. The force of gravity becomes less than the upthrust and the submarine rises.
It rises to the surface by blowing out the water. The less water in the tanks, the less the sub weighs. The force of gravity becomes less than the upthrust and the submarine rises.
How does a sub drive?
A sub has an engine that powers a rear propeller that pushes it forward. To drive to the surface, the sub turns its fins or wings (hydroplanes) at the stern or on the tower diagonally upwards. The sub then uses air to force water out of its tanks to stay on the surface.
"Submarine control surfaces2" by en:User:XLerate - Picture I created with Inkscape, using image from http://www.vectorsite.net/tpecp_08.html as a basis. Licensed under CC BY-SA 3.0 via Wikimedia Commons.
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Alvin - submersible that explores the deep sea
When a sub goes underwater it takes up a space that was made up of water. The sub pushes an amount of water out of the way. And that amount of water is the same shape as the sub. Our imaginary ‘water submarine’ was supported by the water around it. This support is now on the submarine.
Upthrust pushes on objects that sink too. If an object sinks the upthrust is not strong enough to push it upwards. The more water that an object displaces, the stronger the upthrust.
Upthrust pushes on objects that sink too. If an object sinks the upthrust is not strong enough to push it upwards. The more water that an object displaces, the stronger the upthrust.