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How Does the Weight and Hull Shape of an Object Affect  Its Sinking Rate Through Water?


Researched by Blaine H. 1999-2000 


The purpose of this experiment was to determine how much the hydrodynamic shape and mass of an object would affect its velocity when sinking through water. 

I became interested in this idea when watching a Discovery Channel documentary on submarines, which must be able to travel through water at high speeds. 

The information gained from this experiment can be used to help create new and modified hull shapes for submarines and boats so they can travel more quickly and more efficiently.  This will also help architects to design new bridge support columns that will let water flow around them more easily. 



My first hypothesis is that a shape with heavier mass will sink at a faster weight than that of a lighter weight in the water tube. 

My second hypothesis that that a shape with more streamlined hydrodynamic properties will sink at a faster rate in a water tube. 

I base my hypothesis on the physics of aerodynamics and hydrodynamics that say that a more smooth and streamlined shape will be like a wing shape and let more water flow past them easier

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Experiment Design 

The constants in this study were: Same mass in the shapes, same distance to travel, same amount of pressure when it is dropped, same dropper, same water tube. 

The manipulated variables were the different shapes of the objects and the mass of each shape.

The responding variable was the speed the objects traveled through the tube. 

To measure the responding variable I will have someone drop the object on the count of three and I will start the stopwatch, then stop it again when I hear it hit the bottom of the tube.  

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 1  foot clear plastic tube 
   (One end closed off)
1 person to drop
4 wood spheres 
4  wood cones
wood cylinders 
4 wood cubes
1 stopwatch

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1.Make 4 pyramids, 4 spheres,4 cubes and 4 cylinders. 

2.Drill the core out of each shape.

3.Fill one of each shape with 30 grams of shot (shotgun shot).

4.Fill one of each shape with 60 grams of shot.

5.Fill one of each shape with 120 grams of shot.

6.Fill one of each shape with 200 grams of shot.

7.Fill all holes with same amount of glue to seal the hole.

8.Fill the tube with water almost to the top.

9.Drop all of the 30 gram shapes one at a time.

10.Record the data.

11.Drop all of the 60 gram shapes one at a time.

12.Record the data.

13.Drop all of the 120 gram shapes one at a time.

14.Record the data.

15. Drop all of the 200-gram shapes one at a time.

16.Record final data. 

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The original purpose of this experiment was to determine if the shape and mass of an object would affect its freefall through water. 

The results of the experiment were that the more streamlined an object is, the faster of rate it will fall through water.  The cone fell the fastest because it is streamlined, the cylinder fell the slowest and the cube and spherical shape fell somewhere in between those two. See the table and graph below 


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My  first hypothesis was that a shape with a more streamlined hull shape would sink faster in a water tube.

My second hypothesis was that a shape with more mass would sink faster that a shape with less mass. 

The results indicate that this hypothesis should be accepted because the cone sunk at the fastest rate and was the most streamlined shape.  

Because of the results of this experiment, I wonder if an object with a larger surface area could ever fall faster that a streamlined shape.  This may seem impossible unless the larger object has much more mass than the streamlined shape.  

If I were to conduct this project again I would use better shapes for the experiment and use a better water tube than this last time.  I would try to find a clear tube to drop the shapes into and I would use a more accurate form of measurement. 

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Have you ever wondered about how submarines dive and surface that easily?  They are so big and lunky that you would think they would sink to the ocean floor and not be able to surface again.  If you read this report, you will find out how submarines sink and surface among other things.


Submarines are submersible warships used for surprise attacks.  The first submarine plans were made in 1578 by William bourne.  These were the first practical submersibles.  Submarine designs have been changed many times to many different shapes. (See submarine design)   They rise and sink using ballast tanks that they fill to the top with water to sink and empty them to rise. 


Velocity is the speed in which an object is moving in a given direction.  Velocity is shown in time and distance as in miles per hour, meters per hour,etc.  There are two types of velocity, uniform velocity, which means that the distance and the direction traveling are same throughout the whole motion.  Velocity may by variable, which means that the distance and the direction are unequal. 


 The very first working submarine was a rowboat with waterproof hides strapped to the top of it.  The constructor’s name was Cornelius van Drebbel.  He demonstrated his invention invention in 1620, many other attempts to perfect the submarine were made, and only few were excepted.  


 The design of submarines was changed to travel faster.  They are now a cigar or teardrop shape.  This makes them move faster and dive deeper because it reduces the water resistance.  Also, they are built wider and can resist more pressure pushing in on them. This enables them to dive to unbelievably deep levels of water.  

 You have learned this much about submarines and velocity and you might what to continue the research here.  This will enable you to learn more about them.  


1.Encarta, " velocity" Encarta 98, 1998 
2.Lucille b. Garmon, Ph.D., "velocity" World Book Encyclopedia, 1999 
3."Submarines"World Book Encyclopedia, 1991 
4."Submarines"Encarta, 1999 
5."Submarines" ,Discovery Channel 


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