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Submarine: How to sink? How to float?


Introduction: (Initial Observation)

Have you ever tried to push a ball under water? Have you noticed how hard it is? And how it gets harder as you try larger balls? Submarines are actually like a huge ball or a ship. Have you ever wondered how can they go under water? or how much force is needed to push them down?
Inside a submarine is empty space for the most part and workers are working there and living there for many months. Submarines are among the most amazing machines.

In this project you will study the forces that make a submarine go under water and come back up to the surface. Find out what is the relation between the size of a submarine and the force needed to take it down.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.  

Project advisor

Project plan:

Before you start any project, you must make a note of what you are planning to do. Such note is called a project plan. This is a sample:

  1. Search the encyclopedia and the Internet for information about submarine.
  2. Gather information about the history of submarine.
  3. Gather information about the design and the structure of submarine.
  4. Prepare a design for a home made submarine that can sink and float under my command or control.
  5. Design an experiment I can use to measure the force needed for submarines to sink.

Information Gathering:

Find out about submarines and how they are able to sink and float. Read books, magazines or ask professionals who might know in order to learn about the effect of size on the force needed for a submarine to go under water. Keep track of where you got your information from.

Following are samples of information you may find:

submarine is a specialized watercraft that can operate underwater. Most major navies use submarines. Submarines are also used for marine and freshwater scienceand for work at depths too great for human divers.

Nuclear powered submarines and other large submarines are classed as ships, but are customarily referred to by their crews as boats. The term U-Boat is sometimes used in English, this comes from the German word for submarine, ‘U-Boot’, itself an abbreviation for Unterseeboot. Modern attack submarines are known as fast attack subs and generally operate in the hunter-killer role. Large subs carrying strategic nuclear missiles are known as “boomers” in the United States Navy, and “bombers” in the Royal Navy.


Alexander the Great descends into the sea in a glass barrel. Alexander’s relentless energy and apparently limitless ambition drove him to explore remote parts of the world inhabited by strange peoples and monsters, investigate the wonders of the heavens and the depths of the sea, and seek out the secrets of true wisdom and immortal life.




Cornelius Jacobszoon Drebbel was a Dutch inventor of first navigable submarine in 1620.

Drebbel only had elementary education (which included Latin) but had no university education.



The word submarine was originally an adjective meaning “under the sea”. That is why some firms who make  diving gear but not parts for submarines, called their work “submarine engineering”. “Submarine” as a noun meaning a submersible craft originated as short for “submarine boat”; older books (for example Twenty Thousand Leagues Under the Sea) always call it a “submarine boat”.

Archimedes’ Principle

Archimedes’ principle is the law of buoyancy. It states that “any body partially or completely submerged in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the body.” The weight of an object acts downward, and the buoyant force provided by the displaced fluid acts upward. If these two forces are equal, the object floats. Density is defined as weight per volume. If the density of an object exceeds the density of water, the object will sink.


All the above information are gathered from the Internet. Click on source links for the sources of the information.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

How does the size of a submarine affect the force is needed to sink it?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable (also known as manipulated variable) is the size of the submarine (bottle or jar submarine model).

Dependent variable (also known as responding variable) is the force (weight) needed to sink the submarine. Weight may be measured using a scale or the relative weight may be expressed with the number of marbles needed to sink the jar)

Constant is the type of water used in the experiment.

Controlled variable is the temperature. (Do all your experiments in the same room temperature).


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
This is a sample hypothesis:

A smaller submarine needs less force or weight to sink. My hypothesis is based on my observation of the balls I was trying to push under water.

This is another sample hypothesis:

A larger submarine needs less force or weight to sink. A larger submarine is heavier because it is larger, so it needs less additional force or weight to sink.

Your experiment results may or may not support your hypothesis. If your hypothesis is not correct, you will have to reject your own hypothesis later.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: Make Your Own Submarine

Build your own submarine. Discover the principle of buoyancy in your kitchen sink or bathtub!

All you need is:

  • a plastic soda or water bottle with cap (any 16 oz, 20 oz or 2L bottle will do)
  • a flexible straw
  • modeling clay
  • adhesive tape (PVC electrical tape)
  • 7 quarters
  • 2 rubber bands
  • bathroom tub, kitchen sink or large bucket filled with water
  • aluminum foil

Here’s what you do:

Empty the bottle and make a hole in the cap large enough for the straw to fit through (This is easiest to do with a hammer and large nail, so ask an adult to help). Now make two holes in line with each other along one side of the bottle. Tape the quarters together in one group of three and one group of four. Using rubberbands, secure the 4-quarter group below the hole nearest the bottle’s bottom and secure the 3-quarter group underneath the uppermost hole. Fit the shorter end of the straw through the hole in the bottle’s cap and seal with modeling clay. Put the cap back on the bottle.



Now, fill up the bathroom tub, kitchen sink or large bucket with water. Hold your “submarine” underwater so that it fills with water and sinks (be sure to keep the open end of the straw out of the water). Now, blow into the straw and watch what happens.

Here’s how it works:

The submarine filled with water has negative buoyancy and is denser than the surrounding water, so it sinks. As air is blown into the submarine, it gains positive buoyancy and is less dense than the surrounding water, so it rises.

Experiment pictures:

In this bottle submarine the air hole is made on the side, not on the cap. This will make it easier to control the submarine and allow it to go up and down horizontally.

A soft plastic tube about 3 feet long is inserted into the hole.






Some chewed bubble gum is used to seal the hole around the plastic tube.





PVC tape also known as electrical tape is used around the neck of the bottle to hold the tube in place.






I attached a heavy piece of lead on the other side of the bottle (opposite the tube hole) and secured it there with some more PVC tape. I used the lead rod because I had it available. You may use any other heavy metal instead. A long metal piece will help to maintain the balance; otherwise, one end of the submarine may be heavier than the other side.




Lead is a soft metal; so I simply bent it to the size of the bottle.
Two other small holes are made at the bottom of the submarine for entering and exiting water. I made one hole close the front and one hole close to the back.





When I placed the submarine in water, the lead piece automatically moved down and water started to enter the submarine from the bottom. As the water was entering the bottle, air was exiting from the tube. I could use my finger to close the end of the plastic tube to stop the air and water flow would stop as well.




In a few seconds enough water entered the submarine and made it sink.

I could bring it up again by blowing into the tube.





Experiment 2: How Does a Submarine Dive?

Can you make a submarine dive?

Navy sailors do it everyday. Here is an experiment that demonstrates the principle that allow a submarine to dive. All you need is:

  • a tall, narrow jar (like an olive jar),
  • a rubber sheet (it would also work to cut the end off a rubber balloon,
  • a medicine dropper, and
  • water



  1. Fill the jar almost to the top with water.
  2. Put the medicine dropper in and squeeze the bulb just a bit. Allow only enough water into the dropper so that it is just floating at the top.
  3. Now, put the rubber sheet or balloon over the mouth of the jar. Stretch it as far as you can and use the strong rubber band to hold it.
  4. Press down on the sheet with your hand. What happens? Now, remove your hand. What happens? Why?

Here’s how it works:

When you press on the rubber sheet, the air has less space in the jar and so it pushes down on the water more. This increases the water pressure and adds more water to the dropper. The added water causes the dropper to sink. When the pressure on the sheet is released, the air resumes its normal space and exerts less pressure on the water. The extra water pushed into the dropper is released, and the dropper rises to the top.

Whether a submarine is floating or sinking depends on the ship’s buoyancy. Buoyancy is controlled by the ballast tanks, which are found between the submarine’s inner and outer hulls. A submarine resting on the surface has positive buoyancy, which means it is less dense than the water around it and will float. At this time, the ballast tanks are mainly full of air. To submerge, the submarine must have negative buoyancy. Vents on top of the ballast tanks are opened. Seawater coming in through the flood ports forces air out the vents, and the submarine begins to sink. The submarine, ballast tanks now filled with seawater, is denser than the surrounding water. The exact depth can be controlled by adjusting the water to air ratio in the ballast tanks. Submerged, the submarine can obtain neutral buoyancy. That means the weight of the submarine equals the amount of water it displaces. The submarine will neither rise nor sink in this state. To make the submarine rise again, compressed air is simply blown into the tanks forcing the seawater out. The submarine gains positive buoyancy, becomes less dense than the water and rises.

Experiment 3: Make Marbles Float

Have you ever wondered how heavy objects can float? A ship made of heavy steel carries thousands of heavy cars and it can still remain floating on water. This experiment shows how heavy objects can float.


  • a tub filled with water
  • marbles (rocks work too!)
  • a jar with lid (the only requirement is it be small enough to fit inside the tub)


  1. Gently drop the marbles one by one into the tub. Do they float or sink?
  2. Close the jar lid tight and place into the tub. Does it float or sink? (Hint: If the jar sinks, get a new jar!)
  3. Now, take the marbles and jar out of the water. Add one marble to the jar, replace the lid and place it into the water. Does it still float?
  4. Add another marble, replace the lid and put it back in the water. Does it float now?
  5. Keep adding marbles until the jar sinks.
  6. Why does the jar still float when it has a couple of marbles inside when all the marbles sink if they are not in the jar?

Here’s how it works:

The marbles are denser than the surrounding water, so they sink. This is the basic principle behind Archimedes’ Principle. The closed jar filled with air is less dense than the surrounding water. It has positive buoyancy. Adding marbles to the jar affects its weight and thus its density. If enough marbles are added, the jar will sink because it is negatively buoyant.

Experiment 4: Make Your Own Periscope

Introduction: Submarines use a device known as periscope to see above the water. Periscope in submarine is a vertical retractable telescopic pipe with mirrors and lenses. The upper end of the periscope will come out of the water so the underwater staff can see what is happening above the water and be aware of the nearby land and other vessels.

Construction of a periscope is a valuable addition to a submarine project.

How can I use a periscope?

Have you ever wanted to be able to see what’s on top of the refrigerator or around the corner? Now, you can, using the same method Submariners use to see above the water’s surface while they are submerged.


  • a long narrow box
  • 2 small square mirrors
  • scissors


Start with the long narrow box and make the viewholes. Do this by cutting two rectangular holes in the box: one at the top and the other at the bottom on the opposite side.

Next, you need to insert the mirrors. These should be set at 45-degree angles opposite each hole. You can cut slits in the sides to insert the mirrors and use tape to hold them in place.

Now, you can spy on your siblings around corners or see if the grass really is greener on the other side of that tall fence!

Here’s how it works:

Images in front of the top hole are reflected from the top mirror into the bottom mirror where they can be seen through the bottom hole. Submarine periscopes operate very much the same way except on a bigger scale and with magnifiers to help Submariners view distant objects clearly.

Experiment 5: How does the size (Volume) of a submarine affect the force needed to sink it.

Introduction: Submarines need to get very heavy in order to go under water. In other words the only force that can pull a submarine down is its own weight. The weight of a submarine comes from the weight of its structure, equipment and load (passengers). Are these enough to sink a submarine? How much force (weight) is needed to sink submarines with different sizes?


  • a tub filled with water
  • marbles (rocks work too!)
  • Three different size jars with lid


  1. Measure and record the volume of each jar.
  2. Get the smallest jar, place one marble in it, close the lid and place it in the tub. Does it sink or float? If it floats, add one more marble and try it again. Continue this until the jar sinks. Record the size of the jar and the number of marbles it took to sink.
  3. Repeat this with the two other jars and find out how many marbles it take to sink each jar.

Your results table may look like this:

Volume of the jar Number of marbles to sink the jar
200 cc
400 cc
600 cc


  • cc is the abbreviation of cubic centimeter.
  • Instead of the number of marbles, you may record the total weight of the jar with its contents. This is especially good if you don’t have marbles and you want to use sand or small rocks instead. We recommend to measure and record the weights using a gram scale (metric system); however, it is acceptable to measure the weight in ounces as well.

Make a graph:

Make a bar graph to visually demonstrate your results. Make three vertical bars; one bar for each of the jars you test. Under each bar write the size of the jar. The height of the bar will represent the number of marbles or the total weight that made a jar to sink.

Experiment 6: Make a Chemical Submarine


These submarines are operate by a chemical reaction inside the submarine. Some submarines use Alka-Seltzer while others use baking soda and vinegar.

How does it work?

The Chemical submarines use the concept of density to float and sink. When baking soda and Alka-Seltzer meet vinegar and water, respectively, they bubble up and either displace water or expand the sub. This decreases the mass or increases the volume, decreasing the density (mass over volume) enough to make it float. After the reaction calms, the sub regains its previous state (more mass or less volume) causing it to sink again.

Purpose: The purpose of this experiment is to build a submarine that will change density in a tank of water enough to allow it to rise and sink repeatedly.


  • Small container
  • Alka-Seltzer
  • Weight
  • Masking tape
  • Plastic wrap


  1. Tape the weights to the bottom of the container.
  2. Cut a hole in the side of the container, close to the bottom.
  3. Wrap the Alka-Seltzer in a small piece of plastic wrap and hang it inside the container, as close as possible to the top.
  4. Cut about 5 holes in the plastic wrap.
  5. Fill up the container up to about 3/4th.
  6. Hold the hole with your finger so the water does not drain and then close the cap.
  7. Drop the bottle in water, and watch.

What will happen?
Initially the water has no contact with Alka-Seltzer and the bottle sinks because of the heavy weight. At the bottom of the tank the bottle falls on its side. That is when the Alka-Seltzer gets wet and produce gas. The pressure of gas will push some water out of the hole, reducing the total mass of the bottle. The bottle will rise at this time and come to the top.

What happens next?

After a while the produced gases may dissolve in water and cause a vacuum that will suck in some more water and make the bottle heavy again. If this happens, the cycle will repeat.

In good conditions this cycle may repeat a few times.

What can I use as heavy weight?

Lead and bismuth are heavy metals used as weight for fishing. You can use some PVC tape and attach a few pellets on the side of the bottle.

Iron pieces, bolts, nuts and coins are good too; however, you need much more of them. Before you hang the Alka-Seltzer bag, do a test to make sure that your bottle can sink slowly. If it floats, you need more weight or more water.

Materials and Equipment:

List of materials may vary based on your experiments. This is a sample list of materials:

  • A tub filled with water
  • marbles (rocks work too!)
  • Three different size jars with lid
  • Sand and rocks (enough to fill up the jars)
  • Gram scale
  • a plastic soda or water bottle with cap (any 16 oz, 20 oz or 2L bottle will do)
  • a flexible straw
  • modeling clay
  • adhesive tape (PVC electrical tape)
  • 7 quarters or other heavy metal pieces.
  • 2 rubber bands
  • bathroom tub, kitchen sink or large bucket filled with water
  • aluminum foil

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


If you do any calculations, write your calculations in this part of your report.

To calculate the volume of a cylindrical jar you must first measure the height and the diameter of the jar. Calculate the radius (half of the diameter). Take the square of the radius and multiply it by 3.14. This will give you the area of the cylinder base. Multiply this number by the height of the jar to get the volume.

Summery of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.