Introduction: (Initial Observation)
Everyone has experienced the fact that things feel lighter under water than they do out of water. You may also have noticed that it is easier to float (swim) in salt water than fresh water.
This is due to a buoyant force upward. The buoyant force is equal to the weight of the liquid that the object displaces. If the liquid is denser, then the buoyant force is greater. Steel sinks in water, but floats in mercury.
Other possible titles for this project are:
1. Effects of Density
2. Visualize Density
3. Floatation Magic
The third title is only good if you can successfully submerge the egg in the middle of the jar.
Find out about floatation. Read books, magazines or ask professionals who might know in order to learn about the factors that may cause an object float or submerge. Keep track of where you got your information from.
(The information you gather – along with what you already know- together form your background information. ) This is a sample.
What is buoyancy?
Buoyancy is the tendency or capacity to remain afloat in a liquid or rise in air or gas. Buoyant objects have a lower density than the liquid or gas they are in. For example a blimp has a lower density than air and wood has lower density than water. That is why wood floats on water and blimps rise in the air.
What is density?
Density is the ratio of mass to volume in metric system. you can also think of that as the mass of 1 cubic centimeter of anything. The following examples will help you to understand and calculate the density.
Q. 150 cc of water is 150 grams. What is the density of water? (or the mass of 1 cc water).
A. Density of water= 150/150 = 1 g/cm³
Q. A piece of oak wood masses 35 grams and has a volume of 50 cubic centimeter. What is the density of oak wood?
A. The density of oak = 35g / 50cm³ = 0.70 g/cm³
Q. A piece of iron masses 157 grams and has a volume of 20 cm3. What is the density of iron?
A. The density of iron = 157g / 20cm³ = 7.85 g/cm³
To find the density of any object, you need to know the Mass (grams) of the object, and its Volume (measured in mL or cm³). Divide the mass by the volume in order to get an object’s Density.
Please note that cc (cubic centimeter, cm³) and ml (milliliter) are the same volumes; however, ml is only used for liquids while cc is used both for solids and liquids.
How does the egg density compare to water?
Eggs normally sink in water. In other words an egg has a higher density than water. The density of pure water is 1. This means that one milliliter of water weights one gram. The density of an egg is slightly more than one. So one milliliter of an egg is heavier than one gram. If we want to have an egg to float in water, we must increase waters density. To do this we can dissolve some salt or sugar or any other water soluble substance that has a higher density into the water. For example, since salt has a higher density than water, salt water has a higher density than pure water.
Followings are properties of table salt (Na Cl, Sodium Chloride).
- Crystals or white crystalline powder
- Transparent and colorless in crystalline form, rather like ice
Crystallizes in the isometric system, usually in the form of cubes
Soluble in water (35.6g/100g at 0°C and 39.2g/100g at 100°)
Slightly soluble in alcohol, but insoluble in concentrated hydrochloric acid
- Melts at 801°C and begins to vaporize at temperatures just slightly above this
- boiling point 1,413°C
- Hardness of 2.5 on the MHo scale of hardness
- Specific gravity of 2.165
- Non combustible – Low toxicity
- Hygroscopic – absorbs moisture from damp atmospheres above 75% relative humidity.
As you see the density of salt is 2.165 which is more than double the density of water.
Applications of Buoyancy:
One of the useful applications of buoyancy and Archimedes’ principle are to the experimental determination of density. (See how)
Buoyancy has many industrial applications. By knowing and understanding buoyancy you can sink and float the material as you wish. You can do this just by changing the density of liquid. This method is especially used for separation of minerals. For example most copper ores have only about 2% copper and copper compound in them is mixed with lots of soil. Buoyancy is used to bring the copper ore to the surface where it will be separated.
Buoyancy is also the main factor in the following:
- Ice on a lake
- Swim bladders in fish
- Scuba divers
- Aquatic plants (such as water hyacinth)
Floatation is also a mineral separation process, which takes place in a water-mineral slurry. In this method the difference in density is used to separate the pure minerals from unwanted soil that has a different density.
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.
Following are some sample questions/ purposes for this project.
The purpose of this project is to understand the effect of salt on the density of water and floatation of objects. The main question for this project is:
How does the amount of salt in water affect the floatation of egg? (Experiment 2)
Some other related questions are:
- Does the size of an egg affect its ability to float?
- Does the color of egg affect its ability to float?
- Does the size of a glass jar filled with water affect the ability of egg to float?
Need a problem statement? This is a sample:
Materials may sink or float in water depending on their density. We need to have some control on this condition and be able to sink or float them as we need. This is especially important for us when we are separating a few different materials and we want some of them sink and some others float.
Note: This method of separation is already being used to separate minerals from each other and metals from soil. It is also used in recycling where plastics, papers and metals must be separated from each other.
How to measure the density of liquids?
To measure the density of any liquid (like water, saltwater, orange juice, alcohol,..) you will need 2 things. First you need a measuring tool to precisely measure the volume of liquid in milliliters.
Then you need a balance scale or gram scale to measure the mass of the liquid in grams. (Mass is the same as weight at sea level. In reality balance scales measure mass, not weight).
When you have these two values, then you divide the weight by volume. The result will be the density. For example if 50mL of liquid weights 53 grams, then the density is 53/50=1.06 g/ml.
To measure the volume of the liquid you may use a graduated cylinder, a graduated burette or a graduated pipette. For example if you have a 10mL pipette, you can fill it up to the 10mL marking and transfer the liquid to a cup or weighing dish. If you need 50ml you can repeat that 5 times.
How to make a 5% saltwater?
Weight 5 grams of salt and transfer it to a 100 ml graduated cylinder. Then add water up to the 100ml marking. Swirl the cylinder until the salt is fully dissolved.
Instead of a 100 mL graduated cylinder you can use any other measuring cup or beaker as long as it is marked for 100mL capacity.
With the same method you can make any other concentration of saltwater. For example if you start with 7 grams of salt and add water up to the 100mL marking, then your solution will be a 7% solution.
You can also increase the solute (salt) and solvent (water) at any ratio. For example in our 5% saltwater example you could use 50 grams of salt and add water up to the 1000mL marking.
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.
This is how you define the variables for the main question of this project (tested in experiment 2)
The independent variable (the one that we set; also known as manipulated variable) is the amount of salt in water.
The dependent variable (also known as responding variable) is the status of the egg in water (sink, submerge, float).
The control variable is water temperature. (We control the temperature because variations in temperature may cause variations in the density of water. Make sure all water or saltwater you use are at room temperature, and do all experiments in the same day and in the same room.)
Another way of defining the dependent variable is :
The dependent variable (also known as responding variable) is the density of salt-water.
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.
Following is a sample hypothesis for the above question.
Since the density of salt is more than the density of water, adding salt to water will increase the density of the mixture (solution). If the density of water becomes more than the density of the egg, then the egg will float. (Experiment 2)
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: What is the density of egg?
Introduction: The density of pure water is 1. In other words the weight of 1ml water is 1 gram (ml=milliliter=1:1000 Liter) . Objects with a density of less than 1 will float on the water. Objects with a density of more than 1 will sink to the bottom of water. In this experiment we test the density of egg.
Place a 1000ml graduated cylinder on a scale and fill it up with 200ml of pure water. Record the total weight of the cylinder and water.
Carefully place an egg in the cylinder. Record the volume increase and weight increase.
Divide the weight increase by volume increase to find out the density of the egg.
In one experiment, the volume of the egg was 51ml and the weight was 57 grams. So the density of egg will be calculated as:
Density of egg=57 : 51 = 1.176 g/cc
cc means cubic centimeter. cc is the same as milliliter.
What is the density of your egg?
Experiment 2: How much salt will it take to make an egg float ?
This is the main experiment for this project
In order to find the salt concentration that floats the egg, status of an egg in water samples with different amounts of salt can be examined.
For this experiment you will need:
- A plastic or glass jar,
- A measuring cup or graduated cylinder to measure the amount of water
- A gram scale to weigh the salt. Gram scale is a scale that can measure in grams. (Also see the Materials and Equipments section in this project guide)
- Fill 2/3rd of a clear plastic or glass jar with water. Measure and record the amount of water that you are using for this experiment. You will need either the volume or the mass (weight) of water.
- Carefully place an egg at the bottom of that jar. Egg will simply sink and remain at the bottom.
- Prepare some salt. For every 1000 grams of water (one liter), have about 500 grams salt. The salt that you are using must be in the form of fine crystals or powder so it can dissolve easily. Record the mass of salt that you are starting with.
- Start adding some salt and stir the solution carefully.
- Continue that until the egg starts to rise.
Measure the amount of salt that is left over and use that to calculate the amount of salt that is used. (Subtract remaining amount from initial amount)
- Use the amount of water and the amount of salt that is used to calculate the concentration of salt water that can float an egg.
Concentration=(mass of salt)/(mass of salt + mass of water)
In other words first you add the mass of salt and the mass of water to calculate the total mass. You will then divide the mass of salt by total mass of salt water.
Need a Control Group?
Place a similar egg in another container of water, but don’t add any salt to that. That will be your control group. You will observe that the egg in the control group does not float, so you will be sure that the floatation of egg in your experimental container is due to the added salt.
Need a Data Table or Results Table?
The result of this experiment is one single value, so you will not need a data table. If you need a data table for your project, you can repeat your experiment 3 or 4 times and enter the results in a table. For example you may get a small white egg, a large white egg, a small brown egg, and a large brown egg. Try the experiment with each of these eggs and write the results in a table like this:
|Egg type||Salt Concentration floating the egg|
Make a bar graph:
You can use a bar graph to visually present the results in the above table. Make one vertical bar for each type of egg you try. Write the name or the type of egg under each bar. The height of each bar will represent the salt concentration that floated that egg. For example make a 21 cm tall bar to show the concentration of 21%.
This is a common question asked about this experiment:
1. How much salt will it take to make an egg float?
2. What’s my controls?
1. We don’t provide results.
Keep adding salt until the egg floats. Keep track of the amount of salt you are adding.
2. Control is another container of water and egg that you do nothing with that. In other words you don’t add any salt. In this way when the egg starts to rise in the container that you are adding salt, you can be positive that adding salt caused the egg to rise, not an unknown environmental condition.
Experiment 3: How does salt affect the density of water?
In this experiment you will measure the density of water without salt and with different amounts of salt. (If you need a graph for your science project, this is the experiment that you need to do.)
For this experiment you need a metric scale that measures grams. You will also need a measuring cylinder to measure the volume of salt water.
Make different salt solutions starting from 1% (By weight or by volume; you choose!) salt and go up to 25% salt.
For each solution measure the density and record it in your results table.
To measure the density, measure the weight and the volume of the water and then divide the weight by volume. (Measure the weight in grams and measure the volume in milliliters or cubic centimeters).
Your results table may look like this:
|Salt Solution (by weight)||Density|
How to make a 5% by weight salt solution? To make a 5% solution, you weight 5 grams of salt and then add water to that to make it 100 grams.
If you are good in math, you can also calculate the density of different salt solutions.
If you want to measure it and you don’t have much time, just measure the density of 5%, 10%, 15%, 20% and 25% salt solutions. Since the graph is linear (Straight line), it makes no difference how many different salt solutions you test.
You use the above table to make a graph. In the graph, you mark the point that the density of solution is the same as the density of egg. That is where the egg can remain submerged without sinking to the bottom or floating on the top.
This is a sample graph that shows the relation between the concentration of salt and the density of saltwater.
Materials and Equipment:
Material used for this project may vary based on the experiments that you choose and the equipment that are available to you. Following are a list of material and equipment used in the above experiments:
- 3 fresh (uncooked) eggs
- a bag of salt (2 lbs). Buy kosher salt or cooking salt from a local grocery store.
- three beakers or any other clear jar
- 500 ML graduated cylinder MiniScience Part#AS2203
- Balance scale (gram scale). It is used to weigh the eggs.
If you cannot obtain a scale:
If you cannot obtain a scale for your experiments, you may try to use a measuring scoop instead. The results will not be very accurate if you use measuring scoops; however, they are good enough for you to complete your project. Make sure to write about your measuring method in your report in order to explain inaccuracy of results. To convert scoops to gram, use the following:
- 1/4 teaspoon tablesalt is almost 1.5 grams.
- One teaspoon tablesalt is almost 6 grams.
- One tablespoon tablesalt is almost 20 grams.
Results of Experiment (Observation):
Egg easily sinks in a drinking water (Right beaker), but it floats in a concentrated salt water (Middle beaker). We were also able to make a salty water that keeps the egg submerged (Left beaker).
For the purpose of display, prepare three deferent jars. First jar will have pure water, Second jar will have saturated salt water and the third jar will have a salt water that has the same density of egg so the egg will remain in the middle.
When the density of the water is exactly the same as the density of egg, it would be difficult to make the egg stay in the middle. It may sometimes come up and sometimes go down. In the above picture, in order to force the left egg to stay in the middle, we filled 1/2 of the jar with saturated salt water. Then we added some pure water to the top of that without steering. Egg will sink in the top half and will stop as soon as it gets to the saturated salt water.
While you add salt to the water, record and calculate the amounts of water and salt for every condition.
To do that, first add the mass of water to the mass of salt. For example if you used 700 grams of water and 150 grams of salt, the total is 850. This will be the total mass of the solution.
Then divide the mass of salt by the total mass of the solution. In this case you divide 150 by 850 and the results is 0.18 (or 18%). With this result you may conclude that salt water with concentration of 18% or more can float a fresh egg.
Numbers provided in this example are not real experiment results.
Summary 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.
In your conclusion you must write how much salt and how much water are required in order for an egg to float.
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.
Following are samples of related questions:
- Can floatation experiment be performed with other materials such as beans and seeds and minerals?
- Can floatation be used as a separation method? (Can you separate sands from seeds or beans with this method?)
The temperature of water also effects its density. Warmer water has less density than cold water. The salt that you buy may not be pure salt. Salt manufacturers normally add other materials to the salt to absorb moisture. If your salt water appeared to be milky, leave it for a few hours until the white milky material added to the salt will precipitate. Then carefully transfer the clear salt solution to a new jar.
Visit your local library and find some physics books with discussions in “Liquids”, “Density” and “Buoyancy”.
Following are some web resources:
The Buoyancy Experiment
Q: Why you have used three different size of beakers shown in the picture?
A: That is what we had available, but size of beaker or container has no effect on results.
Q: Where can I find, or what could be a substitute for the 500ml graduated cylinder and the balance scale (gram scale)?
A: You have many choices. Online they are available at MiniScience.com and other scientific suppliers. Locally, you may have a scientific supplier or photography supplier or teachers store that sell these. Balance scale is also available as kitchen supplies and in some pharmacies. Use a balance scale with precision of 0.1 gram or better.
Q: what is the problem statement of this project ?
A: This project does not have a problem statement. Instead it has a purpose.
You can make up a problem statement if you wish. Any problem that is caused by low density of water can be used as the problem statement for this project. For example one problem is that many children each year drown in pools. Can adding salt to the pool increase buoyancy and reduce drowning? Is it better to fill up the swimming pool with fresh water or salty seawater?
Q: who is the first person to experiment egg buoyancy?
A: There are billions of objects in the world and egg is just one of them. No one will waste time to record who first did the buoyancy test in every one of these objects. Even if they do, it might be wrong. Buoyancy tests have been performed in many different seeds, many woods, plastics, metals, and minerals.
Q: What is the value of the project to society.?
A: The society benefits from the products that are made, filtered or improved by buoyancy method. Buoyancy is used to separate copper minerals, Zinc minerals and many others. It can also be used to clean seeds and beans from sand and other plant parts.
Q: How your findings can be used?
A: Your findings may be used to float eggs, beans or other materials with the purpose of separation and cleaning.
Q: I am having problems coming up with a good Hypothesis for this project the teacher wants my child to use the word buoyancy in her Hypothesis. How would I rewrite the problem statement and formulate a hypothesis based on what I have researched.
We are working with the experiment number 2 where would I find a gram scale.
A: Possible problem: We need to separate the eggs from stones by floatation.
IF we add salt to the water
THEN the buoyancy force of water will increase
BECAUSE the density of salt is more than the density of water.
Gram scales are sold online and in some electronic stores and office suppliers.