Fluids

Fluids

1. Flow Rate

   • Flow Rate is a measure of a fluid's ability to flow.
     • Gases and Liquids have the ability to flow, as they have large spaces between each of their particles. Solids do have spaces between each and every one of their particles, yet these spaces are tremendously smaller than those found in fluids (the particles found in a solid are more compact/tightly packed together).
       • Although all matter has space between each and every one of their particles, these spaces vary in size.
         • Fluids (liquids and gases), have relatively large spaces between each and every particle when compared to the spaces between each and every particle found within a solid.
           • The large spaces between the particles in fluids are large enough to allow for the particles within said fluid to move around and flow.
     • Non-Newtonian Fluids
       • Definition: "A fluid that does not follow Newton’s law of viscosity (the resistance to flow).
         • Non-Newtonian fluids behave more like a solid or liquid, depending on the amount of force that is applied to them.
           • Non-Newtonian fluids flow at a rate that is determined by the amount of external force that is applied to said fluid.
             • For example, when a large amount of external force is applied to a Non-Newtonian fluid (in the case of oobleck), it behaves like that of a solid (has a very high viscosity, as it is unable to flow).
               • If the opposite were to occur (little pressure was applied to the Non-Newtonian fluid, oobleck), the fluid would behave like that of a liquid (has a low viscosity, as it is able to flow).
                 • Examples of these fluids are the following: Peanut Butter, Oobleck, Almond Butter, Chocolate Spread, ect.
                 • A non-Newtonian fluid's reaction to the varying amounts of applied external force are unique to the fluid. For example, when a large amount of external force is applied to Oobleck, it behaves like that of a solid, but when the same amount of force is applied to ketchup (when shaken), it becomes runnier, behaving more like that of a liquid.
         • Regular Fluid Definition: (fluids that behave as gases or liquids, not both) flow at a consistent rate (so their viscosity follows Newton’s law of viscosity).
         • Newtonian fluids, are fluids that follow newton's law of viscosity.
     • Definition: "flow rate is the amount of volume of a fluid moving from one point to another, in a specific amount of time.'"
       • To allow for this movement to occur, there would need to be a large amount of external force that is being applied to the fluids being tested.
         • To effectively find a fluid’s flow rate, many choose to use gravity as their external force.
           • Gravity is used to ensure that the same amount of external force is being applied to all of the fluids being tested, thus making the results unbiased and factual.
             • There are also various other factors that affect a fluid's flow rate, some of them are the following.
               • Angle at which the fluid is poured.
                 • Gravity has more affect on substances, when they are held at a different angle.
                   • With more gravitational pull, comes more force that is applied to said fluid (allowing it to flow faster).
               • A container's surface texture.
                 • If a container is textured (bumpy, has divots, ect.), a fluid may have a harder time (take longer) flowing out of said container, as it must pass over said textures.
               • The opening of the container that one is pouring their fluid out of.
                 • By having a large opening, one is allowing a large amount of fluid particles to escape at once. Thus allowing for the fluid to flow from one point to another with ease.
               • Other external forces, such as wind.
                 • These forces can cause the fluid to flow in a different (faster or slower) way.
               • Temperature of the fluid being tested, as well as the temperature of the room where the fluid is being tested.
                 • Fluids that have been heated, have faster moving particles (flow faster), while fluids that have been cooled, have slower moving particles.
               • The type of container being used.
                 • If the container being used was one that allowed for the user to choose how much fluid escaped from said container or the size of the opening of the container, it would be harder to determine how much fluid is escaping (hard to ensure that the amount of fluid escaping/size of the container's opening is the same for all fluids that are being tested, as the user gets to determine that, based on the amount of pressure put on the handle). Without knowing the exact amount of pressure being applied to the handle of the container, the size of the container's opening and the amount of fluid escaping from said container can vary between fluids that are being tested.
                   • By not having a consistent container opening size, as well as a consistent amount of fluid escaping from said container (this is dependent on the size of the container's opening), one is unable to produce results that are undoubtedly truthful, as there is a large possibility of bias within their experiment, because of these inconsistencies.
               • The factor that has the biggest impact or affect on a fluid's flow rate is it's viscosity/thickness.
                 • Viscosity has the biggest affect on a fluid's ability to flow, as it determines the amount of space between each and every particle inside of said fluid.
                   • The amount of space between particles in a matter, is what determines said matter's ability to flow.
                     • Fluids that take a longer time flowing from one point to another, are quite viscous, as they having smaller spaces between their particles (the particles have less room to move around, thus causing internal friction).
                       • Fluids that take a shorter amount of time flowing from one point to another, are quite thin (not viscous), as they have larger spaces between their particles, giving their particles the ability to flow with ease (without the often occurrence of internal friction).
                         • Example of fluids with a low flow rate are the following.
                           • Water - 20 ml/s
                           • Vegetable Oil - 7.48 ml/s
                             • The higher the amount of ml per second, the lower the viscosity.
                           • Pure Maple Syrup - 6.44 ml/s
                       • Examples of fluids with a low flow rate (quite viscous) are the following.
                         • Honey - 0.21ml/s
                         • Corn Syrup - 0.25 ml/s
                           • The lower the amount of ml per second, the higher the viscosity.
                         • Molasses - 0.227 ml/s
                         • Dish Soap - 0.569 ml/s
   • One must divide the volume (the specific amount of a fluid they measured), by how much time it took said fluid to flow from one point to another.
     • By doing this, one can easily compare fluids’ flow rates, as well as determine which fluid is most viscous, as this formula allows for one to observe how much fluid escaped in 1 second, a unit that can allow us to compare the flow rate of various fluids.

2. Viscosity

   • The measure of a fluid's resistance of applied force to flow.
     • Viscosity is less formally known as the measure of a fluid's thickness.
       • Fluids that are quite viscous, behave similarly to that of a solid.
         • Solids are unable to flow, as the spaces between each particle within a solid are not large enough. Yet, solids do experience some sort of movement (vibration), as particles in all types of matter are always moving.
           • So, if a fluid behaves like that of a solid, we can immediately assume that this fluid is quite viscous (and has a hard time flowing).
             • When looking at this on a molecular level, one can easily see that fluids that behave like that of a solid have smaller spaces between each and every one of their particles.
               • Let's further understand internal friction.
                 • Internal friction is the friction that occurs between particles within all types of matter. Internal friction is the amount of bumping/rubbing between particles.
                   • When there are lower amounts of internal friction within matter, the matter is usually less viscous.
                     • This is because the particles bump into each other less often, allowing for the substance to flow or not resist external pressure with ease.
                       • When external pressure is applied to matter, the amount of space between each and every particle determines the matter's viscosity.
                         • The amount of space between each and every particle within matter is not only the determining factor of a substance's viscosity and flow rate, but density too.
                           • A fluid's viscosity is determined by the amount of internal friction within said fluid. The amount of internal friction within a fluid is dependent on the amount of rubbing/bumping that occurs between particles.
                             • The amount of rubbing/bumping of particles, is then dependent on the size of the spaces between each and every particle.
           • As a result of the large amount of particles within solids , there are very few spaces between particles. This then allows for internal friction (friction between particles), to occur quite often.
             • Internal friction then slows down the movement of particles within a solid, to that of a mere vibration.
       • The two main factors that affect a fluid's viscosity are cohesion and adhesion.
         • Cohesion
           • Cohesion is the attraction of molecules that are like (the same).
             • When molecules are quite cohesive, they stick to each other, as a result of the electrical attraction between like molecules.
               • This electrical attraction between molecules allows for the molecules to stick to each other, forming structures.
                 • The cohesion of these molecules on the surface of a fluid, is known as surface tension.
                   • Cohesion creates surface tension, then allowing for light-weight objects to be placed on said fluid.
               • Fluids that have a large amount of cohesion between their molecules, are often times quite viscous.
                 • Molecules that are cohesive, have a harder time flowing, as the act of cohesion eliminates the possibility of large amounts of space between molecules (they are unable to slip over each other).
           • Examples of cohesion, are the following.
             • Penny Lab!
               • If one were to drop water molecules onto a penny, the water molecules would form a spherical shape.
                 • This shape would be created as a result of cohesion and then, surface tension.
                   • As all of the molecules dropped onto the penny were like (they were all water molecules), this resulted in them bonding together and creating surface tension.
                     • This bond is what allowed the water molecules to form a spherical shape.
                       • This shape was held, until the maximum capacity of water molecules was reached, then causing the water to deform the spherical shape.
             • Insects sitting on a pond, without braking through the water.
               • Molecules within a pond are all like, as a pond is made up of water molecules.
                 • As all of these molecules are like (the same), bonds are created.
                   • As a result of the bonding of molecules on the surface of the pond, surface tension is then created.
                     • As a result of the creation of surface tension, the insect was able to stay on top of the water, without falling into said water. The attraction of water molecules (the surface tension) was larger than the gravity pulling the insect down.
         • Adhesion
           • Adhesion is the attraction between unlike particles (particles that are not the same). It is also known as the opposite of cohesion.
             • When a substance adheres to something that has unlike particles from those found within said substance, it is displaying adhesion.
               • Examples of adhesion are the following.
                 • Drinking a glass of milk.
                   • When one drinks a glass of milk, they often get a "milk moustache". This a result of adhesion.
                     • The milk inside of the glass has stuck (or adhered) to the unlike particles on one's face.
                       • Then causing the milk to stick onto one's face.
                 • A glass of water.
                   • The attraction between the particles in the water and on the glass are responsible for the curved top surface of the cup. This is known as meniscus.
                     • The curve exists, as a result of adhesion.
                       • The water molecules within said glass, will adhere to the particles of the glass (as they are unlike), causing the formation of a curve.
     • If fluid's show a large amount of resistance to the applied external force, they would be classified as quite viscous.
   • When testing a fluid's ability to flow or resistance to flow, two measures are most commonly used, Viscosity and Flow Rate.
     • Although one formula measures a fluid's ability to flow, while the other measures a fluid's resistance to flow, the data that they both collect help determine a fluid's degree of thickness.
   • What is the purpose of viscosity?
     • Without viscosity, we would be unable to live our everyday lives. It is more than necessary that we have fluids of different thicknesses.
   • What is the purpose of viscosity?
     • Without viscosity, one would be unable to survive. Fluids of varying thicknesses are more than necessary.
       • If one's blood was the same thickness as peanut butter, it would have a harder time flowing throughout their body, thus spending less time completing it's various vital roles within the body.
         • Also, if one's oxygen was the same thickness as ketchup, they would constantly choke on it, as one is unable to breathe in a fluid of that thickness.

3. Density

   • Density is a measure of all matter, not only fluids and is considered to be a characteristic property.
     • When defined, density is, "A substance's degree of compactness" or " The amount of mass per unit of volume within a substance".
       • The two determining factors of a substance's density, are it's mass and volume.
         • Volume, is the amount of space a substance takes up.
           • These factors then come together to form the formula to calculate density, mass divided by volume.
             • People often think that because a substance takes up a large amount of space, it will most definitely be quite dense/heavy.
               • This is most definitely wrong.
                 • Density is mainly dependent on a substance's mass. The formula for density is simply finding how much mass, is in one unit of volume, so that it can be easily compared with/to other substances.
                   • For example, people often ask the following question regarding weight, "If you have a pound of feathers and a pound of bricks, which is heavier?", the obvious answer to this question, is that they are both equivalent in weight, as they both weigh a pound. But people often forget about the density aspect of this.
                     • To get an equivalent amount of feathers to bricks, one is going to need a lot more feathers.
                       • Therefore, the volume these feathers take up is a lot larger than the volume the bricks take up, as bricks are quite heavy in comparison to feathers (they have more mass per unit of volume), meaning that one is not going to need as many.
                         • So, if one were to take 1 unit of volume of each substance, one could easily see that there are more brick particles (the mass of brick per unit is larger), than the feathers. This can also be inferred, through the bricks' ability to reach a pound in weight with a volume that was tremendously smaller than the feathers'.
                           • This then proves that bricks have a larger amount of mass in any given volume when compared to that of feathers'. For any given amount of volume, there would always be many more brick particles than feather particles.
         • Mass is the measure of the amount of matter in an object or substance.
         • What states of matter are typically the most and least dense?
           • Solids are usually the most dense state of matter, as the spaces between each and every particle within a solid are substantially smaller than that of a fluid (the particles are packed very closely together). Making solids more compact or have a higher degree of compactness.
           • Liquids are usually the second most dense state of matter, as the particles in that of a liquid are closely packed together when compared to a gas, yet not when compared to a solid.
           • Gases are the least dense matter. They have rather large spaces between their particles (are not tightly packed together), when compared to both solids and liquids.
           • The spaces between each particle, determine the mass (amount of matter) in the substance being observed. If the amount of matter in any given volume of said substance is large, then we can assume that this substance is quite dense.
         • Often times while making predictions of a substance's density, many think/use viscosity, as one of the factors that could determine a substance's density.
           • Although when examined on a molecular level, substances with a high viscosity tend to be quite dense, this is not the case with all substances, therefore eliminating it's relevance or use in determining something's density.
             • Fluids that are quite viscous, are usually quite dense too and vise versa. This is because of the following.
               • Both viscosity and density depend on the amount of space between each and every particle within a substance, as the outcome of using both unit of measures are determined by that factor.
                 • Regarding viscosity, if a substance has a large amount of space between each of their particles, they have the ability to flow with ease, without creating internal friction. The larger the spaces between particles, results in lower amounts of internal friction between particles, thus allowing for the substance to have very little resistance to the applied external force, making the substance not very viscous.
                   • Therefore, the viscosity and density of a substance is determined by the same main factor.
                 • Regarding density, if a substance has a large amount of space between each of their particles, this means that there are fewer particles within 1 unit of volume of said substance, as there are a large amount of spaces between particles (spaces that are not filled with matter that could possibly increase the density of said substance).
             • Oil and water. When given the question, "which substance is denser, oil or water?" many choose oil, as it has a higher viscosity than water, but in fact, water is denser.
               • When put together in a glass, the oil floats above the water particles, as the water is denser.
                 • This occurs as a result of oil particles being larger than water particles, this variation in size allows for water particles to tightly pack together, while oil particles cannot.
                   • The obvious separation between the two fluids also occurs as a result of them being immiscible (unable to mix together of create a homogeneous mixture).
               • When oil spills occur, the properties of oil (it's density) allow for it to be collected after the spill, with a lot more ease. This is a result of oil being less dense than water (floats on top of water), as well as it being an immiscible fluid.
                 • To collect said oil after an oil spill, floating booms surround and enclose the affected area, thus not allowing the oil to contaminate any other parts of the water. This then allows for the affected are to be treated (taken out of the water with various collection devices) with ease.
               • Another example that relates to water and density is the following.
                 • Although water is a fluid, when frozen (changed into the solid state of water, ice) it becomes less dense. Usually fluids as they begin to decrease in temperature (cool down), begin to become more dense, as their particles begin to move at a slower rate and become more closely packed together. In the case of water making the transformation to ice, once the temperature of the water lowers past 4 degrees Celsius, the water molecules begin to spread apart.
                   • Water molecules continue to do this until the water has completely made the transformation from liquid to solid.
                     • Another example of density comparison is the following.
                       • Someone throws two items into a lake, 1 item is a hollow log, while the other is a rock. The rock sank to the bottom of the lake, while the log floated on top, why is this?
                         • Various factors regarding buoyancy helped to keep the large hollow log afloat, while sinking the compact, yet still heavy, rock. When only talking about density's affect on this outcome, the following reasons come to mind.
                           • The large hollow log stayed afloat, while the rock sunk to the bottom of the lake, because the log was less dense than the rock.
                             • Although the log took up a larger amount of space than that of the rock, when observing the amount of matter in any given amount of volume of both substances, one can easily observe the larger amount of matter (rock particles) in said amount of volume of the rock. The lack of matter within said hollow log allowed, for it to float, while the heavy, yet compact rock sunk.
     • This is because all types of matter have some sort of density.
   • What is the importance of density?
     • Without density and having a general understanding of density, many would be unable to do a variety of things. This includes the variety of things done by boat.
       • When one thinks about the key factors that come into play when designing a boat, many immediately think of buoyancy. While buoyancy is of great importance in the means of keeping any water-craft safe and afloat, one must also take into account density, these two units of measure go hand-in-hand (density and buoyancy).
         • Without a strong understanding of density, boats would most definitely sink, as those who are creating said boats, could create boats that are bulky, compact and carry a large amount of passengers. These attributes that could be possibly added to the boat's design, are not conducive to the boat's ability to be buoyant.

4. What are Fluids?

   • Fluids are classified as, "a substance that has no fixed shape and yields easily to external pressure".
     • When one thinks of a fluid, they immediately think of gas and liquid matter, as they are categorized as fluids.
       • Fluids play vital roles within our everyday lives Without them, the simple task of living would be unachievable.
         • Some of these important fluids, are the following.
           • Blood
             • Blood is one of the most important fluids within our body.
               • It transports oxygen throughout the body to various cells and tissues.
                 • On top of this, different blood cells play different crucial roles within the body.
                   • White blood cells are an important part of the immune system, as they protect the body from disease.
                   • Red blood cells specifically, supply various cells and tissues with oxygen.
           • Mucus
             • Although many see mucus as a disgusting by-product of sickness, it helps to trap bacteria, and stop it from entering our body.
           • Oxygen
             • Oxygen is a necessity for everyday life. Without it, many of our vital organs would be unable to do their jobs.
               • When tissues and cells do not receive enough oxygen, they begin to die. When this occurs, over time, or instantly (if lack of oxygen is so extensive), one can die.
                 • This is a result of humans being made up of cells, meaning that by losing too many cells, we will die too.
         • What would happen if these important fluids were to not be fluids, but instead, solids? How would this negatively affect us?
           • If fluids transitioned into the state of matter known as a solid, they would be unable to flow.
             • If oxygen was unable to flow, we would be unable to inhale it.
             • If blood was unable to flow, then our various vital organs that need blood, would be unable to function.
             • As we know, solids are unable to flow, while fluids do it with ease.
               • What if the thickness or a fluid's ability to flow changed in a drastic way?
                 • These fluids would have a harder time and almost impossible time performing their important jobs within our body.
                   • If oxygen were to be a lot thicker, we would be unable to breathe it in in without choking.
                   • If blood was to be a lot thicker, it would be unable to transport oxygen to various cells and tissues in an effective manner.
                   • A fluid's ability to flow is known as it's flow rate. A fluid's thickness is known as it's viscosity.
                     • We must have fluids of different thicknesses and flowing abilities, as without that variety, our body would be unable to function.
       • These fluids have the ability to flow. They have this ability, as a result of having large spaces between each and every one of their particles. These spaces allow for movement and flowing of particles to occur.
         • There are two types of fluid flow, laminar flow and turbulent flow.
           • Laminar flow is smooth and regular.
             • Laminar flow occurs when fluids move in orderly lines, along smooth pathways.
               • Laminar flow helps vehicles, such as boats and cars move more efficiently, as the flow of the fluid is moving in a way that reduces resistance on the vehicle.
           • Turbulent flow is choppy and irregular.
             • Turbulent flow does not help vehicles like cars and boats (vehicles that travel through fluids) to be more efficient, as it is increasing the vehicles resistance of the fluid.
           • Examples of both types of fluid flow are the following.
             • Laminar: Pipes and hoses (water is undisturbed by floating debris, as well as there is only one water pathway).
             • Turbulent: Rivers with large rocks and debris inside of them (creates different currents and pathways in the water.
     • Fluids take on the shape of the container that they are placed in, meaning that they do not have a fixed shape.
       • On the other hand, liquids do have a definite volume, as no matter what container they are placed in, there is always going to be the same amount of liquid within said container, even if that amount is shown differently in different containers.
         • Gases do not have a fixed volume, as they will fill any container they are placed in. This is a result of there ability to disperse their gas particles throughout said container, simply by making the spaces between each gas particle larger (this a result of diffusion).

5. Buoyancy

   • When an object is submerged in any type of fluid, the fluid exerts pressure on said object (person or thing). The upward pressure that is exerted on said object, is known as buoyancy.
     • This buoyant force is what prevents various objects that are less dense than the surrounding fluid (water), from sinking into said water.
       • This is why the act of submerging a buoyant object (like a beach ball) is quite hard.
         • What makes objects buoyant?
           • The main determining factors of a objects buoyancy are the following. It's density, ability to displace water, surface area/volume and the type of fluid said object is going to be placed in/on.
             • As we know, density is the measure of the amount of matter (particles) per unit of volume within an object/substance. If an object were to be denser than the surrounding fluid, said object would sink. This is a result of the surrounding fluid's inability to hold said object, as it is too dense (the amount of particles per 1 unit of volume are more than the surrounding fluid, thus making the object too heavy).
             • Displacement of water. When an object is placed on/in a fluid, the amount of water it displaces is determined by it's volume. Displacement of water is essentially the amount of water that is moved to accommodate an objects entrance or submersion into a fluid (water). When the displacement of water is large, one knows that the volume of said object is large, as the displacement of water is equivalent to the volume of the object. When a large amount of water is displaced, the object that is displacing the water is going to be more inclined to float (experience buoyancy).
               • This also means that the weight of the object being submerged in said water, is equivalent to the amount water that has been displaced, as a result of the submersion of said object.
                 • The amount of water displaced by an object, determines the amount of buoyant force that is applied to said object.
             • The type of fluid an object is being placed in/on, determines whether or not the object sinks or floats. If the object is denser than the surrounding fluid, the object will sink.
               • If the object is less dense than the surrounding fluid, the object will stay afloat.
             • The fluid an object is being placed in, or more specifically, the density of said fluid, is a very important factor.
               • The density of said fluid determines whether or not the object being placed in the fluid sinks or floats. In other words, the comparison between the amount of particles in one unit of volume between both the object being placed in the fluid and the actual fluid, determines the object's buoyancy.
                 • If an object has a larger density than the surrounding fluid, said object will sink.
                   • When an object is quite dense, the buoyant force is unable to withstand it's amount of mass, therefore causing the object to sink.
                   • The object will experience negative buoyancy.
                 • If an object has a smaller density than the surrounding fluid, said object will float.
                   • When an object has a smaller density than the surrounding fluid, the buoyant force is able to withstand it's amount of mass, therefore causing the object to float.
                   • The object will experience positive buoyancy.
       • How strong is the buoyant force?
         • The buoyant force is equivalent to the gravitational force that is acting on a floating object.
           • The amount of buoyant force that is being applied to an object is also dependent on the weight of the water that was displaced by said object.
             • On top of this, the buoyant force within a fluid is also dependent on the density of said fluid.
               • For example, different bodies of water vary in density.
                 • Salt water is denser than fresh water, as it contains salt (adds more mass). This then means that salt water exerts more buoyant force than that of fresh water.
                   • To ensure a boat's ability to float in waters that have varying buoyant forces, the Plismoll scale was created. This scale shows/marks the portion of the boat that will be submerged in each type of water.
   • The importance of buoyancy.
     • Without buoyancy, we would be unable to do a variety of things. Some of them are the following.
       • We would be unable to fly pontoons. Pontoons, also known as "sea planes", are planes that have the ability to land on water. This is a result of their effective use of the buoyant force and density.
       • We would be unable to use boats.
         • Without taking density (the density of both the boat and the surrounding water) and the buoyant force that all fluids possess into account, boats would sink.
           • By designing boats that are large and hollow (have a large amount of air within them), the buoyant force has the ability to withstand them (or keep them afloat). As a result of this large amount of air within boats, the density of said boat is not as large as the density of the surrounding water.
             • If one were to compress the boat into one large piece of metal, the metal would most definitely sink, as a result of the lack of air and poor displacement of water. This is why the design of boats' being large and hollow is quite common, as it is the only boat design that can stay afloat (the buoyant force has the ability to only withstand boats of that design).
       • We would be unable to retrieve items that have fallen to the bottom of any body of water, as a result of their tremendous weight.
         • Due to the fact that these items sank to the bottoms of various bodies of water because of their density (and the lack of buoyant force being exerted onto said objects), to retrieve these items, the buoyant force is used.
           • Diesel filled flotation bags have been strapped onto said objects, in an attempt to create a man-made buoyant force.
             • This then allows for the extremely large objects to be brought to the surface with ease.
             • The creation of man-made buoyant force, has not only helped to retrieve lost items, but has also saved the lives of many.
               • Those who are unable to swim, use life preservers and other flotation devices to prevent them from drowning.
     • Buoyancy has not only been a force that has helpful to humans in various means, but has also helped other living organisms. Some of them include the following.
       • For a fish to maintain their position in water, they use a swim bladder sac. This sac is a thin-walled sac, containing mainly oxygen.
         • This sac can expand in size when need be. Thus increasing the fish's volume (they displace more water), while decreasing their density (the amount of air within them increases, thus decreasing the amount of particles per unit of volume ).
           • This then allows for said fish to regain their stability and maintain their position in the water.
         • This innovative creation, has then allowed us to develop an invention similar to that of the swim bladder, yet it is used to maintain a constant position in water for submarines.
           • This innovation is known as the ballast tank.
             • When a submarine is descending, the ballast tank's chambers fill up with water. This action increases the amount of mass within said tank, thus lowering the submarine.
               • When a submarine is surfacing, it expels the excess water that was collected to descend into the body of water. This has been done to lessen the amount of mass within the submarine.
                 • Compressed air then floods into the chambers, helping to further alter (decrease) the density of the submarine.
                   • By decreasing the density of the submarine, the buoyant force now has affect on the submarine (has the ability to bring it back to the surface).
                   • By adding compressed air into the ballast tank's chambers, one is changing the ship's mass-to-volume ratio, as the amount of mass within the chamber is lessening.