SummaryIn this activity, students learn about ocean currents and the difference between salt and fresh water. They use colored ice cubes to see how cold and warm water mix and how this mixing causes currents. Also, students learn how surface currents occur due to wind streams. Lastly, they learn how fresh water floats on top of salt water, the difference between water in the ocean and fresh water throughout the planet, and how engineers are involved in the design of ocean water systems for human use.
As resources on land become more and more scarce, engineers are looking to the ocean to meet needs for food, minerals and transportation. Engineers develop systems for operation on, and in, the ocean. A huge area of interest for ocean engineering is hydrodynamics and acoustics — to communicate underwater using sound. To understand sound, engineers must understand the fluid dynamics of the ocean and sound waves. Engineers also work on many other projects involving the ocean, including the design of seaports, ships, and submarines. They work with geologists to design better equipment for drilling oil deep on the ocean floor and with marine biologists to monitor natural ecosystems within the ocean. Lastly, there are engineers who design equipment that can measure the temperature and depth of the ocean from space.
After this activity, students should be able to:
- Compare and contrast the properties of salt water in the oceans/seas and freshwater elsewhere on the planet.
- Describe mixing caused by currents in the ocean, including the effects of warm and cold water as well as surface currents.
- List several systems that engineers are designing that involve the ocean as a resource.
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Each TeachEngineering lesson or activity is correlated to one or more K-12 science,
technology, engineering or math (STEM) educational standards.
All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN),
a project of D2L (www.achievementstandards.org).
In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics;
within type by subtype, then by grade, etc.
Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.
All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).
In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.
Each group needs:
- Two copies of the Oceans Away Worksheet
Activity 1 – Follow that Current
- Two colored ice cubes (colored with dark food coloring)
- Clear baking dish or see-through container
- Warm or hot water
Activity 2 – Currents in the Wind
- A spice, such as oregano, that will show up in clear water
- Clear baking dish or see-through container (Note: This can be the same container used in activity 1)
- Room temperature water
Activity 3 – Fresh Water Floats?
- Food coloring (dark colors work best)
- Two clear glass jars, or container that will allow students to see a clear lineation between the salt and fresh water (Note: this should be taller than the baking dish used in activities 1 and 2.)
- Room temperature water
To share with the entire class:
- Paper towels to clean up
- Spoons for adding salt to water and stirring in food coloring
- Ice tray to make ice cubes
- Access to a freezer
- Pitcher(s) to fill up baking dishes and cups with water.
Have you ever looked at a map of the world or a globe? (If possible, display a globe or world map for the students to see.) Look at all the water on the Earth. A lot of the bodies of water are connected to each other. In fact, the world's oceans are really one large world ocean. Where on Earth do you think the water would be warmer or colder? (Answer: Warmer: equator; colder: poles) What do you think happens when the cold water from the north and south poles meets the warm water from the equator? Well, the answer is currents. Currents are movements of water in an ocean (or lake). The ocean's water currents move continuously around the Earth and actually help keep its temperatures regular. How can the ocean help keep the temperatures of the Earth regular? Well, the ocean water affects the temperature of the atmosphere in part by absorbing incoming radiation from the sun, and then the ocean currents mix the warm and cool waters together, keeping the temperatures from getting too hot.
Did you know that the oceans make up about 97% of the water on Earth? That's a lot of water! How many oceans are there? Can you name them? Until the year 2000, there were four oceans: Pacific, Atlantic, Indian and Arctic. In the spring of 2000, the International Hydrographic Organization announced a new ocean, the Southern Ocean, which surrounds Antarctica and extends up to 60 degrees latitude.
Have you ever tasted ocean water? Well, it's very salty! It is not something you would want to drink normally because of its high salt content. The amount of salt in water is called its salinity. The salinity of the oceans and seas are different throughout the world, but the average salt content is 2.2 pounds of salt for every cubic foot of water. The saltiest seawater is in the Persian Gulf, which is 40 o/oo (parts per thousand) salt (source: Palomar Community College, http://www.palomar.edu/oceanography/salty_ocean.htm). The least salty water is in the Polar Regions, where the water is mixed with melting ice and heavy precipitation. Consider an iceberg: it sits in the ocean for centuries. It is composed of fresh or salt water? (Answer: Icebergs are formed when parts of the Antarctic icesheet break off. The icesheet, which covers the continent, is formed by snow and ice falling on inland areas, thus icebergs are freshwater. Source: Australian Antarctic Division, http://www.aad.gov.au/default.asp?casid=6288)
What do you know about the ocean? Today, we are going to look at some properties of fresh water (in our case, water from the tap) and ocean water. We are going to learn about how water mixes and how salt water moves in fresh water. These are important concepts for engineers to understand when designing any kind of system that deals with ocean water.
Current : A tidal or non-tidal movement of lake or ocean water.
Equator: The imaginary line on the Earth's surface that exactly divides the Earth into northern and southern hemispheres.
Freshwater: When referring to a resource, water that is specifically not salty.
Poles: Refers to the North and South Poles, the areas at the furthermost north and south points on Earth.
Salinity : Containing salt.
Before the Activity
- Gather materials and make copies of the Oceans Away Worksheet.
- Make dark-colored ice cubes for Activity 1 – Follow that Current.
With the Students
Activity 1 – Follow that Current
- Fill up baking dishes three quarters of the way to the top with warm/hot tap water.
- Give each group 2 colored ice cubes (prepared ahead of time).
- Ask them to observe what happens to the colored ice cubes. Where does the colored water go? Have them write a description of what they see on their Oceans Away Worksheet.
Activity 2 – Currents in the Wind
- Fill up baking dishes three quarters of the way to the top with room-temperature tap water. (Or, if continuing from Activity 1, use the resulting water.)
- Sprinkle a small amount of spice over the water.
- Direct students to lightly blow over the surface of the water.
- Ask students what happens to the spices as you blow over the surface of the water? Have them write the answer on their worksheet.
Activity 3 – Fresh Water Floats?
- Pass out two glasses to student groups.
- Fill the first glass three quarters full with room-temperature tap water.
- Fill the second glass one quarter full with room-temperature tap water.
- Have students add one spoonful of salt to the second glass (the one with less water) and stir. They should continue to add salt until no more salt will dissolve in the water (one or two spoonfuls should be enough).
- Have students add a drop or two of food coloring to their salt water.
- Pour the colored salt water slowly into the glass containing the clear fresh water.
- Ask students what happened to the salt water on top? Did it sink or float? Have them write an answer on their worksheet.
- If time permits, do activity again except put colored salt water in first and add clear fresh water on top. What happens to the fresh water on top? Does it sink or float?
Do not use water that will run the risk of burning students; warm to hot water from the tap is sufficient.
Have supplies ready and pitchers of water filled to make the transitions between activities run smoothly.
When students are directed to blow lightly across their baking dish of water, remind them not to spit or blow hard. The water will easily leave the dish and blow onto another student.
Discussion Questions: Solicit, integrate and summarize student responses. Ask the students:
- Would you expect water on different parts of the planet to be warmer in some places than others? Why?
- Where do you think ocean water would be warm/cold?
- How is ocean water different than water you find in lakes and streams?
Activity Embedded Assessment
Group Question: During the activity, ask the groups:
- Why do you think the colored water from the ice cube moves to the bottom of the pan of warm water? Do you think a similar movement might also happen in the ocean? (Answer: Cold water sinks and warm water rises; this is what causes underwater currents.)
- How does wind cause surface currents? (Answer: Wind blows over the surface and causes currents that move water on the surface around.)
- Does salt water float on top of fresh water, or does salt-water sink into the fresh water? (Answer: Salt water sinks into the fresh water because salt water is heavier than fresh water. Therefore, fresh water floats on top of salt water.)
Question/Answer: Ask the students and discuss as a class:
- What is a current? (Answer: The movement of water in an ocean or lake.)
- What are two causes of currents? (Answer: Temperature differences and wind.)
- Does salt water float on top of fresh water, or sink? (Answer: It sinks. This happens because salt water is denser than fresh water.)
- Would you want to drink water from the ocean? Why or why not? (Answer: No, it is very salty and would eventually dehydrate you due to the consumption of too much salt.)
Engineering Ocean Water: Have the students generate a list of all the different things they can think of that use water. (Examples may include daily activities such as brushing teeth, drinking, watering plants, cleaning dishes, as well as other things like ships, submarines, dams, fish tanks and swimming pools.) Next, have the students circle all of the things on their list that use salty ocean water. Then, discuss with the students the remaining items on their lists. Most of their list probably needs fresh water. Engineers are designing systems that would take the salt out of ocean water and turn it into fresh water. Have the students circle any items on their list that might be able to use ocean water if the salt were removed. (They should have all items circled now.) Their second set of circles show why it is important for engineers to understand the properties of the ocean as a resource, especially with the small amount of fresh water that is available for use and the high demand of activities that need fresh water every day.
Students could make a map of the world's oceans and draw in the major ocean currents, labeling them as a surface current or an underwater current.
- For upper grades: The activity can be set up as an example of how to use the scientific process. Students could write a hypothesis, define their variables, conduct the experiment and then state their conclusion.
- For lower grades: The activities could be done as demonstrations or stations could be set up so that students don't have to do as much of the set up.