Unit A Lesson A9 Buoyancy
Completion requirements
Lesson A9: Buoyancy
Video Lesson
Why do some objects float in water while other objects sink? Watch this video to learn about how density affects the buoyancy of substances.
Lesson A9: Buoyancy
Figure A.3.9.1 – Icebergs are large chunks of floating ice.
Figure A.3.9.2 – Ice floats on liquid water because ice has a lower density than water.
Floating Ice
Ice and liquid water are made of exactly the same type of particles. Why then, does solid ice float on liquid water?
The answer involves density. Water expands into a larger volume when it freezes. This is different from most substances, which contract into a smaller volume upon freezing. Water particles spread apart and freeze into special crystal patterns. Whenever particles of a substance expand into a bigger volume, the density of the substance is reduced. As a result, ice’s density of 0.91 g/mL is slightly smaller than water’s density of 1.00 g/mL, and so ice is buoyant on water.
Ice and liquid water are made of exactly the same type of particles. Why then, does solid ice float on liquid water?
The answer involves density. Water expands into a larger volume when it freezes. This is different from most substances, which contract into a smaller volume upon freezing. Water particles spread apart and freeze into special crystal patterns. Whenever particles of a substance expand into a bigger volume, the density of the substance is reduced. As a result, ice’s density of 0.91 g/mL is slightly smaller than water’s density of 1.00 g/mL, and so ice is buoyant on water.
Reading and Materials for This Lesson
Science in Action 8
Reading: Pages 50–52
Materials:
Raw eggs (3), tall drinking glasses (3), water, salt, spoons, glass measuring cup, turkey baster, small cups (9), honey, corn syrup, maple syrup, homogenized milk, dish soap, vegetable oil or canola oil, rubbing alcohol, baby oil, food coloring
(red, blue, and yellow), dish towel, sugar, measuring spoons, raisins, club soda or lemon-lime soda.
Most rivers and lakes don’t freeze completely during the winter. Rivers and lakes have a layer of ice floating on top of liquid water. Sometimes ice layers are very thick. 30 cm of ice on a lake can support a car! However, you should never walk or drive
on ice unless it has been tested and confirmed to be safe.
Fish and other aquatic organisms live in the water under ice. Inuit people in the Arctic relied on digging holes in large sheets of floating ice to fish for food during long winters. Many Canadians still enjoy and depend on ice fishing during the winter.
Fish and other aquatic organisms live in the water under ice. Inuit people in the Arctic relied on digging holes in large sheets of floating ice to fish for food during long winters. Many Canadians still enjoy and depend on ice fishing during the winter.
Figure A.3.9.3 – Cold liquid water is found under the ice surface of most frozen lakes.
Figure A.3.9.4 – To ice-fish, the Inuit drill holes into floating ice.
Watch More
Why Does Ice Float?
Watch this video to learn more about why ice floats on water.
Watch this video to learn more about why ice floats on water.
Icebergs are large floating pieces of ice in the ocean. Watch this video to learn more about icebergs.
The Inuit ice-fish for food in the winter. Watch this video to learn more about ice fishing in the Arctic.
Figure A.3.9.5 – It is easier to float in saltwater than freshwater.
Figure A.3.9.6 – The Dead Sea contains a high concentration of salt.
Figure A.3.9.7 – Dead Sea water has a higher density than fresh water.
Salt Water Swimming
It is much easier for a person to float in the salty ocean than a freshwater lake. Salt water contains a higher concentration of salt than fresh water, which makes it denser. Substances with a higher density exert more buoyant force.
Even though people are more buoyant in saltwater compared to freshwater, you still need to use proper swimming techniques to stay afloat in the ocean. You can’t lay on your back and read a book in ocean water. However, there is one place on Earth where this is actually possible!
The Dead Sea is located on the border of Israel, Jordan, and the West Bank. It is the lowest land on Earth, at 400 metres below sea level. The Dead Sea is an inland salt lake, that is almost 10 times as salty as the ocean. The high concentration of salt makes the Dead Sea much denser than the ocean, and as a result, much more buoyant than the ocean. People float effortlessly in the Dead Sea.
It is much easier for a person to float in the salty ocean than a freshwater lake. Salt water contains a higher concentration of salt than fresh water, which makes it denser. Substances with a higher density exert more buoyant force.
Even though people are more buoyant in saltwater compared to freshwater, you still need to use proper swimming techniques to stay afloat in the ocean. You can’t lay on your back and read a book in ocean water. However, there is one place on Earth where this is actually possible!
The Dead Sea is located on the border of Israel, Jordan, and the West Bank. It is the lowest land on Earth, at 400 metres below sea level. The Dead Sea is an inland salt lake, that is almost 10 times as salty as the ocean. The high concentration of salt makes the Dead Sea much denser than the ocean, and as a result, much more buoyant than the ocean. People float effortlessly in the Dead Sea.
Watch More
The Dead Sea is Really Dense!
It’s easy for humans to float in the Dead Sea, but can a heavy bowling ball float in the Dead Sea? Watch this video to find out.
It’s easy for humans to float in the Dead Sea, but can a heavy bowling ball float in the Dead Sea? Watch this video to find out.
Try It!
Salty Sea Egg
Try this experiment to test how changing the density of water affects the buoyancy of an egg.
Materials:
Try this experiment to test how changing the density of water affects the buoyancy of an egg.
Materials:
- 3 raw eggs
- 3 tall drinking glasses
- Water
- Salt
- Spoon
- Glass measuring cup
Instructions:
- Fill one glass three-quarters full with water.
- Fill a second glass three-quarters full with water. Add 5 spoonfuls of salt. Stir the salt into the water until it is all dissolved.
- Fill the third glass half-full with water. Add 5 spoonfuls of salt. Stir the salt into the water until it is all dissolved. Slowly pour more water from the measuring cup into the glass, until the glass is three-quarters full.
- Carefully add 1 raw egg to each glass. What do you observe?
- Watch the results of this experiment here:
Questions:
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
The egg was more dense than the fresh water. The force of gravity on the egg was greater than the buoyant force on the egg, so it sank.
The egg was less dense than the salt water. The force of gravity on the egg was less than the buoyant force on the egg, so it floated.
The third glass contained a bottom layer of saltwater and a top layer of freshwater. The egg was less dense than the saltwater so it floated to the top of the saltwater layer. However, the egg was more dense than the freshwater layer, so it
could not rise any higher and float on top of the freshwater layer.
Lesson Activity
Virtual Buoyancy Experiment
Problem:
Hypothesis:
Problem:
How buoyant are different objects in different liquids? In this virtual experiment, you will test the buoyancy of five different objects in three different liquids. How buoyant are charcoal, egg, gold, iron, and oak wood in fresh water, salt water,
and vegetable oil?
Hypothesis:
A hypothesis is a testable answer to a scientific question. In other words, what do you think the result of this activity will be?
A hypothesis is a testable answer to a scientific question. In other words, what do you think the result of this activity will be?
Hint: The five objects are charcoal, egg, gold, iron, and oak wood. The three liquids are fresh water, salt water, and vegetable oil. Before you make your hypothesis, it will help to have more information. Refer to the Determining Density activity you completed in Lesson A8, and copy the densities you calculated for each object into the Observations Table below. You can also find the densities in the document you will download below.
Now, it’s time to make your hypothesis. Which objects do you think will float in fresh water? Why? Which objects do you think will float in salt water? Why?
A hypothesis is a testable answer to a scientific question. In other words, what do you think the result of this activity will be?
Hint: The five objects are charcoal, egg, gold, iron, and oak wood. The three liquids are fresh water, salt water, and vegetable oil. Before you make your hypothesis, it will help to have more information. Refer to the Determining Density activity you completed in Lesson A8, and copy the densities you calculated for each object into the Observations Table below. You can also find the densities in the document you will download below.
Now, it’s time to make your hypothesis. Which objects do you think will float in fresh water? Why? Which objects do you think will float in salt water? Why?
Download & Website:
DOWNLOAD this document. It provides a space for you to write your hypothesis. Also use the document to write your observations and analysis answers that come later in this activity.
DOWNLOAD this document. It provides a space for you to write your hypothesis. Also use the document to write your observations and analysis answers that come later in this activity.
Go to the website http://ippex.pppl.gov/interactive/.
Click on the link for the "Virtual Density Lab".
Click on the "Open in a new window link".
Instructions:
- For the liquid choice, click on water.
- Drag each object to the pail of liquid. Observe if each object floats or not, and record these observations on the table below.
- Change the liquid choice to salt water, and repeat Step 2.
- Change the liquid choice to vegetable oil, and repeat Step 2.
Observations:
| Object
|
Density
(g/mL) |
Buoyancy in
Fresh Water (Density = 1.00 g/mL) |
Buoyancy in
Salt Water (Density = 1.03 g/mL) |
Buoyancy in
Vegetable Oil (Density = 0.89 g/mL) |
|---|---|---|---|---|
| Charcoal | ||||
| Egg |
|
|
|
|
| Gold | ||||
| Iron | ||||
| Oak wood
|
Questions:
Think about the following questions very carefully. Refer to your observation table. Then, type or write your answers in the document you downloaded. When you have your answers, click the questions below for feedback.
Think about the following questions very carefully. Refer to your observation table. Then, type or write your answers in the document you downloaded. When you have your answers, click the questions below for feedback.
Charcoal and oak wood floated in fresh water because they both had densities lower than fresh water’s density of 1.00 g/mL.
The egg, gold, and iron sank in fresh water because they all had densities higher than fresh water’s density of 1.00 g/mL.
Charcoal, the egg, and oak wood floated in salt water because they all had densities lower than salt water’s density of 1.03 g/mL.
Gold and iron sank in salt water because they both had densities higher than salt water’s density of 1.03 g/mL.
Charcoal was the only substance that floated in vegetable oil because it had a density lower than vegetable oil’s density of 0.89 g/mL.
The egg, gold, iron, and oak wood sank in vegetable oil because they all had densities higher than vegetable oil’s density of 0.89 g/mL.
Sharing:
Congratulations on completing this activity! Consider sharing your completed work (or any thoughts and experiences you might have regarding this activity) in the course Sharing Forum. You can also email your completed work to your teacher and ask for feedback.
Congratulations on completing this activity! Consider sharing your completed work (or any thoughts and experiences you might have regarding this activity) in the course Sharing Forum. You can also email your completed work to your teacher and ask for feedback.
Try It!
Density Tower
Try this experiment to layer liquids with different densities.
Materials:
Try this experiment to layer liquids with different densities.
Materials:
- Tall glass or vase
- Turkey baster
- 9 small cups
- Spoons
- Honey
- Corn syrup
- Maple syrup
- Homogenized milk
- Dish soap
- Water
- Vegetable oil or canola oil
- Rubbing (isopropyl) alcohol
- Baby oil
- Food coloring
- Dish towel
- Protective eyewear (when handling rubbing alcohol)
Safety Warning
This activity uses rubbing (isopropyl) alcohol, which is quite safe if handled correctly. It would be best to wear eye protection and avoid contact with skin. If you do make direct contact with rubbing alcohol, rinse thoroughly with water.
Instructions:
- Fill each of the 9 small cups one-third full with each of the 9 fluids. Wear protective eyewear when handling rubbing alcohol.
- Add 3 drops of food colouring to the water and the rubbing alcohol cups. Stir the food colouring into the liquids with a clean spoon.
- Slowly pour the honey from the cup into the tall glass. Pour the honey into the center of the glass, making sure that no honey touches the sides of the glass.
- Slowly pour the corn syrup on top of the honey. Pour the corn syrup slowly into the center, so the fluids don’t mix.
- Draw up the maple syrup from its cup with the turkey baster. Carefully and slowly, squeeze the maple syrup on top of the corn syrup.
- Wash and completely dry the turkey baster.
- Repeat steps 5 and 6 for homogenized milk and dish soap.
- Repeat steps 5 and 6 for the rest of the liquids in this order: water, vegetable oil, rubbing alcohol, and baby oil. However, instead of squeezing out the liquids in the middle, carefully and slowly squeeze them down the side of the tall glass.
- Watch this video to see this experiment and its results:
Questions:
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
Honey had the largest density, so it stayed at the bottom of the density tower.
Baby oil had the smallest density, so it floated on top of all the other fluids in the density tower.
If you added the fluids to the tower randomly, they would float and sink depending on their relative densities. This would cause the fluids to mix. Adding fluids from greatest to smallest density prevents the liquids from mixing, and allows
you to create a tower with distinct layers.
Try It!
Sugar Rainbow
Try making artistic fluid motion with milk, food colouring, and dish soap. Watch this video to see an example of this activity.
Materials:
Try making artistic fluid motion with milk, food colouring, and dish soap. Watch this video to see an example of this activity.
Materials:
- Sugar
- Water
- Food colouring (red, blue, yellow)
- Spoons
- Measuring spoons
- 6 small cups
- Turkey baster
- Tall glass or vase
- Dish towel
Instructions:
- Fill each of the 6 small cups half full with water.
- Add the following ingredients to the cups and stir until they are dissolved:
Solution Sugar Food Colouring
Purple 10 tablespoons
2 drops red, 1 drop blue
Blue 8 tablespoons 3 drops blue
Green 6 tablespoons 2 drops yellow, 1 drop blue
Yellow 4 tablespoons 3 drops yellow
Orange 2 tablespoons 2 drops yellow, 1 drop red
Red no sugar
3 drops red
- Draw up the purple solution with the turkey baster. Carefully and slowly, squeeze the purple solution into the middle of the tall glass.
- Wash and completely dry the turkey baster.
- Draw up the blue solution with the turkey baster. Carefully and slowly, squeeze the blue solution down the side of the tall glass.
- Wash and completely dry the turkey baster.
- Repeat steps 5 and 6 with the solutions in this order: green, yellow, orange, red.
- To view a version of this experiment and its results, watch this video:
Questions:
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
The solutions contained different concentrations of sugar and water. This made each solution have a different density. Sugar solutions with lower concentrations and densities floated on top of sugar solutions with higher concentrations and densities.
The purple solution had the largest concentration of sugar, with 10 tablespoons. As a result, it also had the largest density and stayed at the bottom of the tower.
The red solution contained no sugar, so it had the smallest density. This made it possible for the red solution to float on top of the more dense sugar solutions.
Connections
Figure A.3.9.9 – To swim at the surface, fish relax the muscles around their swim bladders.
Figure A.3.9.10 – To dive deep, fish tighten the muscles around their swim bladders.
Figure A.3.9.11 – Fish have swim bladders, which enable them to move up and down in water.
>> Fish Buoyancy
Animals that live in water, like fish, need to adjust their depth to catch food and to escape predators. In order to move up and down in water, some aquatic animals can change their density, and as a result, their buoyancy.
Many fish have swim bladders. A swim bladder is like an air-filled balloon inside a fish. Muscles around the swim bladder make it change in size. When the muscles around a fish’s swim bladder tighten, the swim bladder is squeezed smaller in volume. This makes the air in the swim bladder more dense. As a result, the fish becomes more dense and sinks in the water. When the swim bladder muscles relax, the air in the swim bladder expands, becomes less dense, and the fish floats upward.
Watch More
Shark Buoyancy
Sharks don’t have a swim bladder, so how do they move up and down in water? Watch this video to learn about adaptations sharks have to stay afloat.
Sharks don’t have a swim bladder, so how do they move up and down in water? Watch this video to learn about adaptations sharks have to stay afloat.
Try It!
Dancing Raisins
Try this experiment to see how gases affect the density of an object.
Materials:
Try this experiment to see how gases affect the density of an object.
Materials:
- Raisins
- Tall glass
- Club soda or lemon-lime soda
Instructions:
- Pour the club soda into the tall glass.
- Add a small handful of raisins to the glass of club soda.
- Observe the motion of the raisins.
- Watch this video to see this experiment in action:
Questions:
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
Small bubbles of carbon dioxide gas attached to the wrinkles of the raisins. Gas has a lighter density than water, so the gas bubbles caused the raisins to have a lower density and float to the top of the glass.
At the top of the glass, the carbon dioxide bubbles on the raisin wrinkles escaped to the air. Without any attached air bubbles, the raisins returned to their regular density. A raisin has a lower density than water, which makes it sink.
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your
learning.
Unit A Lesson 9 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps – if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
- DOWNLOAD the self-check quiz by clicking here .
- ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
- COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
-
REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
- SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
- CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Be a Self-Check
Superhero!
Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.
A wooden dock floats because its wood is less dense than water. Wood can have a large mass, which makes it heavy to lift. However, as long as the wood’s density is less than the density of water, it will float.
The oily liquid is more dense than water, which is why it is initially at the bottom of the lava lamp. When the oily liquid heats up, its particles spread further apart into a greater volume. This makes the oily liquid less dense than water,
which makes it buoyant on water.
Away from the heat source at the top of the lava lamp, the oily liquid cools. Its particles move closer together into a smaller volume. This makes the oil more dense than the water, reducing its buoyancy and making it sink to the bottom. This process keeps repeating, creating interesting visual effects in the lava lamp.
Away from the heat source at the top of the lava lamp, the oily liquid cools. Its particles move closer together into a smaller volume. This makes the oil more dense than the water, reducing its buoyancy and making it sink to the bottom. This process keeps repeating, creating interesting visual effects in the lava lamp.
The Earth’s solid crust is less dense than the liquid mantle. As a result, the crust floats on the mantle.
The pilot would turn down the burner. Turning down the burner would cool the air inside the balloon. As a result, the particles in the balloon would move closer together, and become more dense, reducing the balloon’s buoyancy in the air. Balloon
pilots can also open a valve at the top of the balloon, allowing hot air to escape. The escape of low-density hot air means the density of the entire balloon increases, causing the balloon to be less buoyant and more likely to sink.
When you take a deep breath, you are adding air to your body. Air has a low density, so when you add air to your body, it makes your body less dense. This helps increase the buoyant force on your body, pushing you upward in the water.