Specific gravity: Everything you ever wanted to know about volume, pressure and more Specific Gravity Part I: What is specific gravity? Grandpa, I kind of understand what gravity is, but what is specific gravity? Isaac Newton, you remember, discovered gravity when an apple fell from the tree and struck the table at which he was seated. He realized there is a mysterious force that pulls everything on Earth toward the center of the Earth. As Newton thought about it, he realized that everything on Earth and in space depended on this very mysterious force called gravity. Without it there would be no life on Earth. One problem in understanding gravity is that gravity does not pull on everything with the same force. Gravity pulls the hardest on gold, silver, iron or any other metal. Gravity has only a small pull on gases like air, helium, or hydrogen. In order to compare the pull of gravity, there needed to be a standard to which it could be compared. It was decided that since water is the most abundant substance on the surface of Earth, water would be the standard. We compare all other substances to water. Water weighs 62 lbs per cubic foot. We call the specific gravity of water 1. If something is heavier per cubic foot, its number will then be greater than 1. If something per cubic foot, weighs less than water, its specific gravity would be a number less than 1. Newton s apple fell down because its specific gravity was greater than that of air. If it fell on water it would float, because the specific gravity of an apple is less than the specific gravity of water, therefore it would float on water. If a piece of wood is up in the air and it falls, it will fall down through the air because its specific gravity is greater than air. If it lands in water it will float on the water because its specific gravity is greater than air and less than water. Different gases have different specific gravities. Let s suppose that we release equal amounts of air, hydrogen, and CO 2 in a closed room. CO 2 has the highest specific gravity of the three and it weighs the most per cubic foot of the three gases. It would sink to the bottom of the room. Hydrogen has the lowest specific gravity of the three. It would be closest to the ceiling. Air has a specific gravity greater than hydrogen and less than CO 2. It would occupy the space between the CO 2 on the bottom and the hydrogen on the top. Is there a relationship between specific gravity and how much something weighs? Absolutely. Gold is twice as heavy per cubic inch as silver. We say gold is twice as dense as silver. What does that mean? We really don t know. It s really another way of saying that gold is so very heavy because gravity, for whatever reason, pulls the hardest on it toward the center of the Earth. Hydrogen weighs much less per cubic foot than gold, because for whatever reason gravity pulls very lightly on the gas hydrogen. It is very important to know materials with a high specific gravity will always seek to fall below materials with a low specific gravity. Water, in particular, will always seek to fall below air.
These are the basic principles which are necessary principles to preserve life on Earth. These basic laws are part of an obvious design. Where there is a design there must be a designer. What a privilege it is to know and serve our designer, God. Grandpa, why does it matter if we know specific gravity or not? Specific Gravity Part II: Why does it matter if we know the specific gravity of a substance? Grandpa, why does it matter if we know the specific gravity of a substance? In some cases knowing the specific gravity of a substance can be the difference between life and death. Water and oil are both liquids. The specific gravity of water is 1 and the specific gravity of oil is less than 1. If an area of water is covered by oil and we wish to remove the oil, we can vacuum the oil off the surface and put the mostly oil with some water in a tall tank. The lighter oil will rise to the surface and the water to the bottom. If we drain the bottom, all the water will come out leaving pure oil. If we have oil or gasoline in a tank, both of which are liquids, and it catches fire, we have a problem. We know that oil or gasoline have a lower specific gravity than water so it will float on the water. If we try to put the fire out by pouring water on the fire, we make the problem worse. The water will sink below the oil while the burning oil will rise above the water and spill over the sides, spreading the fire. We realize that burning oil requires oxygen to burn. If we can remove the oxygen we can put out the fire. How can we remove the air from the top of the oil tank? We know that different gases have different specific gravities. We know that the specific gravity of air is less than the specific gravity of CO 2. We remember that if we place CO 2 in a room with air, the CO 2 would drop to the bottom of the room and push the air up and out. How can we use this knowledge to put out the fire in the tank? Oil cannot burn without air. Oil will not burn with an atmosphere of CO 2. CO 2 is heavier than air, so the fireman pours CO 2 into the top of the tank containing burning oil. The CO 2, which is heavier than air, pushes the air up and out of the tank. Since the oil cannot burn without oxygen, the fire goes out. Knowing the specific gravity of oil, water, air and CO 2 can save our lives. Let s suppose a frying pan with oil catches fire. Never pick up the frying pan. Instead, either put a cover over the fire and when the oxygen is used up the fire will go out, or keep baking soda on the stove and sprinkle it on the fire. The baking soda will turn to CO 2, and the CO 2 will sit on the oil and push the air up and out, and the fire will go out. The fact is that thousands of lives and much valuable property have been saved because of our understanding of the specific gravity of substances. Grandpa, most solids have a specific gravity greater than water so most solids will sink in water. What makes a huge metal boat float? Specific Gravity Part III: What makes a huge metal boat float?
Grandpa, most solids have a specific gravity greater than water, so most solids will sink in water. What makes a huge metal boat float? Many years ago, a very brilliant Greek called Archimedes discovered several very important laws. To illustrate one of them, we take a solid cube of aluminum measuring three inches by three inches by three inches (which equals a volume of 27 cubic inches), and place it in water. The cube will sink to the bottom because it is denser and heavier than an equal volume of water. The water spilled or displaced over the top would occupy a space three inches by three inches by three inches, which is the same volume as the block of aluminum. The weight of the water displaced, however, will be less than the weight of the aluminum block that displaced it. Now we take the aluminum block and we beat it into a lasagna tray. It is a sixteenth of an inch thick and measures one foot by one foot and is two inches high. Even though the shape and volume has changed, the weight is exactly the same. The volume is now 12 inches, times 12 inches, times 2 inches, which equals 288 cubic inches. We fill the water up to the brim of the container. We place the tray in the water. The tray weighs exactly the same as it did before but it barely sinks into the water. Why does it now float and barely sink into the water? The volume has changed from 27 cubic inches to 288 cubic inches. It must be the volume that makes the difference. We weigh the tray. We weigh the water which was displaced. We find that the weight of the water displaced is exactly the same as the weight of the tray which was floating on it. Since the volume changed it decreased the density of the tray, allowing it to float. Archimedes had discovered a law, a very important law. A floating object does not displace its volume. Instead it displaces a volume of water equal in weight to the object resting on it. When the tray was on top of the water, the law for every action, there is a reaction was in effect. The water exerted a force upward equal to the weight of the tray pushing down and the tray floated. The force of gravity was not enough to overpower the reaction of the water pushing up. When the lasagna tray floated, it was not just the specific gravity of the aluminum we were concerned with; it was the specific gravity of 288 cubic inches of air and a little aluminum. Therefore, the aluminum tray plus air, floated on top. The lasagna tray measured 12 inches by 12 inches by 2 inches. That s 288 cubic inches. The combined weight of 288 cubic inches of aluminum and air is much less than 288 cubic inches of water, therefore the tray floats on top of the water. Gravity will not pull the tray below the water. Think of the tray as a ship without a top. To prove this is true, fill the tray to the brim with water and it will sink to the bottom. Once the weight of a substance is greater than the weight of the water it would displace, the substance will sink. If you wish to have a more complete explanation, Archimedes is the man who discovered displacement and he would be a good person to research. Grandpa, I understand why a ship floats, but why does it sink? Specific Gravity Part IV: Why does a ship sink?
Grandpa, I understand why a ship floats, but why does it sink? Let s take our lasagna tray and place it in the water. It floats. Now take a nail and drive the nail through the bottom of the tray, then take the nail out of the tray. We now have a hole in the bottom. Put the tray back in the water. The tray floats in the water, but water is forcing its way up through the hole. There is a basic law we need to understand which is that for every action, there is an equal and opposite reaction. The action is the weight of the tray pressing down on the water. The reaction is the water pressing upward with a pressure equal to the pressure pushing down. As water pours into the tray, the weight of the tray and water increases. Now the weight of the tray plus the water in the tray has increased by the weight of the water. As the weight of the tin plus the water in it increases, the reaction increases. The water is coming up faster, adding to the total weight. The weight continues to increase until the tray s weight and the weight of the water in the tray is greater than the weight of water it displaces. The tray sinks to the bottom. A ship is floating on the surface. Its weight is less than the weight of water it would displace. It strikes an iceberg or there is an explosion below the water line. We now have a hole in the bottom of the ship, below the water line. The weight of the ship is pressing down on the water. For every action, there is a reaction equal and opposite reaction. The water pushes upward against the bottom or side of the ship. Water is pushed upward through the hole in the ship. The air in the ship is lighter than water and is forced upward and out, replaced by heavy water. The ship gets heavier and heavier, causing a greater reaction of water upward. The pressure of water upwards increases, forcing water in and air out. When the specific gravity of the ship becomes greater than the weight of water it displaces, the ship sinks below the waves to the bottom of the ocean. Understanding God s unchanging laws, such as specific gravity and for every action, there is an equal and opposite reaction, allows us to plan and design our surroundings in order to live comfortably. Grandpa, a submarine must be heavier than water. How does it come up to the top? Specific Gravity Part V: A submarine must be heavier than water. How does it come up to the top? Grandpa, a submarine must be heavier than water. How does it come up to the top? Wow, that s a great question. When a submarine sinks, it is heavier than water. When it rises, it is lighter than water. How can that be? In the days when I served aboard subs, the only energy for the sub was provided by diesel engines, which burned oil and oxygen. They could travel at top speed about 18 miles an hour when they floated on top, and that was only at night. The act of burning oil requires a great deal of oxygen. A fire is just fuel combining with oxygen. If we were under water, the only oxygen to
use is in the submarine, and that would be used up in less than a few minutes. That would leave no oxygen for the sailors to breathe and they would die. The bottom of the sub was lined with lead acid storage batteries. The diesel engines ran electric generators. The electricity the generators produced was stored in the lead acid batteries at the bottom of the sub. The sub used the electricity in the batteries to make electric motors operate. The electric motors turn propellers which move the sub at three or four miles an hour at best. The sub could only go very slowly under water at a few miles per hour, and could only stay under for at most 24 hours. After 24 hours, they would run out of air. With today s nuclear subs, they can stay under for six months or more. Only a few batteries remain. There really is no need to store large amounts of energy. A nuclear furnace uses no oxygen, so it can be used underwater while a diesel engine cannot. A diesel engine consumes huge amounts of air. A nuclear engine produces huge amounts of energy. Water is two parts hydrogen and one part oxygen, H 2 O. The energy produced can be used to break down water into hydrogen and oxygen for use on the sub. How does a submarine sink and then rise to the surface? On either side of the main compartment of the sub, there is an iron tank shaped like a cucumber. At the bottom of these tanks are openings to let water in and out. There are no valves to hinder the flow of water in or out. On the top of the tank is a valve to let air out. There is another valve connected to high-pressure air. With both valves shut and the tanks full of air the boat floats on water. When floating on the surface, the total volume of the submarine has a specific gravity less than one. The specific gravity of water is equal to one therefore the submarine floats. When we open the air release valve on the top of the tank, the water reacts to the weight of the sub and pushes the air up and out. The law for every action there is an equal and opposite reaction comes into play. The weight of the water downward causes a pressure of water upward. Since we open the air valve, the water pushes the lighter air up and out. Water flows upward through the opening on the bottom and into the tanks. The sub becomes heavier and heavier as air escapes out of the top and is replaced by water. When the specific gravity or weight of the sub is greater than the water it displaces, the sub sinks. The weight of the ship is fine-tuned until it floats at the depth that they want. How does the submarine rise to the surface? We close the air escape valve and open the valve connected to high-pressure air. The high-pressure air forces its way into the tanks. The air cannot escape out from the top as the escape valve is closed. The air pressure is greater than the upward water pressure created as a reaction to the weight of the sub. The air pressure, which is greater than the water pressure, tries to expand. The only thing that will move is the water below it, which has less pressure pushing upward than the air pushing down. Water is pushed down and out of the bottom and is replaced by lighter, high-pressure air. When almost all of the water is pushed out, the now lighter-than-water sub rises to the surface.
The law concerning specific gravity which tells us that lighter substances rise above heavier substances, and heavier substances sink beneath lighter substances, is one of the most important scientific laws. Without it, life on earth would not be possible. Specific Gravity Part VI: Why does God have icebergs floating in the ocean? Grandpa, why does God have icebergs floating in the ocean? There is no question that it would be dangerous if you crashed into an iceberg. The iceberg, however, moves very slowly. If we know where the iceberg is and the iceberg moves slowly, why should the iceberg be dangerous? The ship Titanic sank because the builders of the ship, the Captain and the officers, defied God and practically dared Him to sink it. The Captain and his officers knew there were icebergs in the area and yet they were going full speed ahead. If you bang your head on the wall and get hurt, is that God s fault? If you know there are icebergs in the area, should you be traveling full speed ahead? The truth is unless there were icebergs on the Earth, nothing could live. Life on earth would be impossible without icebergs. Before we can understand why icebergs are so necessary, we need to understand some laws of science. We take a brick, put it on a scale and weigh it. Now if I take a large bucket of water and place the brick in it, the brick sinks to the bottom. The same size brick weighs more than an equal cubic volume of water. Bricks will sink to the bottom of a bucket of water because they are heavier. Take a block of wood and weigh it. It weighs less than a container of water the same size. Place the wood in the bucket and the wood will float on the top of the water. Wood weighs less than water, so it floats on water. In like manner, cold water is heavier than warm, or hot water. Cold water will always sink below warm water. If that s true Grandpa, then why does a cold iceberg or an ice cube float on water that is not as cold? That, of course, is one of the mysteries of water and all part of God s great plan. Let s say the temperature in the room is 72 degrees and the water is 72 degrees. We fill a container up to the brim. We weigh it and record the weight. We then take the container with water at 72 degrees filled to the brim and place it in the refrigerator, which is at 35 degrees. We return in two or three hours and we find the water level has gone down. We mark it and weigh it. The weight is exactly the same as before. We take the water out into the room at 72 degrees and come back. The level is back up to the brim. We weigh it again, and it s exactly the same. We should have learned that cold water expands as it warms up. The same amount of cold water will fill more space when it becomes hot water. Warm water contracts as it cools. Cold water is heavier per cubic inch than warm water. Cold water placed in a container with warm water will sink to the bottom.
In like manner, as the iceberg melts and becomes very cold water, that very cold water sinks to the bottom of the ocean. It then moves to the south, toward the equator. It joins the cold river of water at the bottom of the ocean which stirs up the pollution on the bottom, bringing it to the surface where it is neutralized by the ultra red rays of the sun. By this process, the ocean is purified. Chemicals and nutrients, which came from the rivers running into the ocean, are also stirred up for the plankton to eat (plankton are at the bottom of the ocean s food chain). As the river in the ocean moves south to the equator, a vast volume of heat is transferred from the area around the equator to the water. This both heats up the water and cools off the equator. Near the equator, the river turns east to the coast of Europe and then north on the west coast of Europe. The heat, trapped in the water, is now slowly released to warm Europe. Rome is the same latitude as Boston. Boston has cold winters. Palm trees could never survive in Boston. Rome, at the same latitude, has mild winters and has palm trees growing. Ireland and England have mild winters thanks to the Gulf Stream. Newfoundland, at the same latitude, has bitter cold winters and heavy snows. The difference is the Gulf Stream. But why icebergs? God makes icebergs to moderate the temperatures of the earth, purify the oceans and provide food and oxygen for plankton and fish. Yes, icebergs can be very dangerous if you are foolish, but life on earth would not be possible without them. Why did God make icebergs? He made them because He loves you.