Does fresh water hold heat longer than salt water? How does water compare to land and what effect does this have on the weather? What factors affect the cooling of land?
Introduction: (Initial Observation)
If you’ve ever been out in the hot summer sun for any length of time, you know that it makes you pretty darn hot. The sands in the beach gets very hot and walking bare foot becomes a painful experience. While sands in the beach are hot enough to cook an egg, water may still be cold. After sunset sands lose their heat very fast while water is still warm. Why does the sand become hot or loses heat so fast, while water is much slower in gaining and loosing heat?
Does such difference affect the climate? We are hoping to find the answer to some of these questions during this project.
Find out about heat retention and other important physical properties of material. Read books, magazines or ask professionals who might know in order to learn about the factors that may affect heat retention. Also learn about specific heat or heat capacity of material as a factor affecting heat retention. Keep track of where you got your information from.
Note: Heat Retention of a substance is the amount of heat that certain amount of that substance can retain in itself. For example water can hold much more heat than wood. If you place a cup of water and a block of wood in the oven for a while, water will absorb and retain more heat in itself than wood (per unit of weight).
In this project we will test and compare the heat retention of different material, not the heat retention of one substance in different temperatures or different physical stats. The reason is that comparing the heat retention of one substance at different temperatures and different physical stats is very complicated and needs more advanced equipment. For example the heat retention of crystal sugar may be different from the heat retention of molten sugar. Also the heat retention of water may be different from the heat retention of ice.
In the example of salt water, heat retention may change based on the density of salt water. So if you are studying the heat retention of salt water, you can repeat your tests with different salt waters with different densities.
You will need to add some more information yourself from books and from the Internet. Having a list of references is an important part of each science project.
Oceans slow warming and cooling in coastal cities
Oceans have a large influence on the climates of coastal cities. They moderate the climates of coastal cities by keeping the winters warmer than they would otherwise be if the city was farther inland and the summers cooler. As you can see in the graphic above, Sioux Falls, SD. has a much larger variation in temperature between January and July than the coastal cities of Portland, ME. and Portland, OR. The main reason for this is that water has a much larger heat capacity than land. In other words, water temperature changes very slowly compared to soil temperature. This is why coastal cities do not warm up as fast as cities in the Plains during spring and summer and why they do not cool down as fast during fall and winter. If it were not for the oceans, coastal cities would have much colder winters and much warmer summers like the cities in the Plains and other inland regions.
Sea breezes help cool places near oceans
A sunny, warm April morning with temperatures in the 70s begins a beautiful spring day in New Jersey. As you and the family go on a picnic to take advantage of the great weather, a sudden chill roars through the region and a stiff easterly wind quickly drops temperatures into the 40s. This often occurs near the coast during early spring warm ups. It is commonly known as a sea breeze. But during the hot days of summer, sea breezes can bring welcome relief from the heat.
Sea breezes form because water heats up much slower than land. Cool air over the ocean is heavier and more dense than the warm air over land. The cool air nudges its way inland and can create a strong wind at the surface. The bigger the temperature contrast between the air temperature inland and the water temperature, the better chance of a sea breeze developing and the stronger it will be.
Some Physical Definitions:
Temperature is the measure of the relative warmth or coolness of an object. Temperature is measured by means of a thermometer or other instrument having a scale calibrated in units called degrees.
Heat capacity or thermal capacity is the ratio of the change in heat energy of a unit mass of a substance to the change in temperature of the substance; like its melting point or boiling point, the heat capacity is a characteristic of a substance. The measurement of heat and heat capacity is called calorimetry.
Specific heat is the ratio of the heat capacity of a substance to the heat capacity of a reference substance, usually water. Heat capacity is the amount of heat needed to change the temperature of a unit mass 1°. The heat capacity of water is 1 calorie per gram per degree Celsius (1 cal/g-°C)
Specific Heat of a substance in relation to water is the same number as the heat capacity of that substance. This is because the heat capacity of water is 1.
What does that mean?
When you warm up an object, you are storing heat energy in that object. For example you may store some heat energy in a rock by placing it on the fire. You may later use the heat energy stored in a rock to warm up your hands. Is rock a good object to store energy? Do other material hold more energy in them?
The amount of heat energy that can increase the temperature of 1 gram rock by 1 degree Celsius is the specific heat capacity of the rock. For example the heat capacity of glass is 0.2 cal/g/ºC. In other words if you have a piece of glass that is 1 gram, you can use 0.2 calorie heat energy to increase its temperature for 1 degree Celsius. The same amount of water gets five times more heat energy to warm up the same amount. So the heat capacity of water is five times more than the heat capacity of glass.
Following table shows the heat capacity of different material.
Specific Heat Capacities Table
|Water (0 oC to 100 oC)||1.000|
|Ice (-10 oC to 0 oC)||0.500|
|Steam (100 oC)||0.480|
|Air (50 oC)||0.250|
Since different material have different heat capacities, the amount of heat that can heat up different material to a certain temperature varies. For example wood will get to a certain high temperature with very little heat. So a hot wood is not as dangerous as hot water.
The purpose of this project is:
- To compare heat retention of fresh water and salt water
- To compare heat retention of water and sand/soil
- Build a simple solar collector to store heat
- Measure heat retention and dissipation in a closed environment
- Use the difference between heat retention of soil and water to explain the climate of coastal cities.
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.
The independent variable is the type of material. Possible values are water, salt water, sand, wood)
The dependent variable is the heat retention.
Constants are heat source, temperature, methods and procedures.
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.
My hypothesis is that pure water will retain more heat than salt water. Also water will retain more heat than sand.
I base my hypothesis on personal observations that in a hot summer evening, soil gets cold faster than water. Water will stay warmer even hours after the sunset. Soil contains salt and many other minerals, so salt water that contains such minerals should have lower heat retention.
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.”
Heat Uptake Experiment (List of material follows)
Note: The older version of this experiment is available here
For heat uptake experiment you may place different material under the sunlight or in a warm oven and record their temperature increase.
For solid material the surface temperature will be measured.
For liquids, sand and powders, thermometer can be inserted in the material or can be mounted on the side of their container.
The most common experiment for heat uptake is comparing the rate of heat uptake of water and salt water.
The other experiment is comparing the heat uptake of water and sand. You may do this experiment with dry sand or with wet sand.
Following is a sample procedure for comparing the heat uptake of salt water and fresh water.
Use tap water as fresh water. Make saturated salt water by adding as much as possible kosher salt to regular tap water. (about 250 grams of salt per liter of water)
- Get two identical glass jars and two identical thermometers. Pass the thermometers from square pieces of cardboards that are slightly larger than the jars openings. Cardboards will hold the thermometers in a way that the bulbs will stay almost in the center of the jar.
- Fill 1/2 of one jar with salt. Label the jar as “SALT WATER”.
- Label the second jar as “FRESH WATER”
- Add water to both jars up to about 3/4 of the top. The water level in both jars must be the same. It won’t matter if the salt is not dissolved in water.
- Place the thermometers in the jars and make sure that both thermometers show the same temperature. If they are not showing the same temperature, keep both jars at room temperature or in a refrigerator until they get to the same temperature.
- Record the starting temperature of both jars and carefully place them in a warm oven. Oven temperature about 80ºC up to 120ºC is recommended. (Adult help and supervision is required)
- Open the oven every 5 minutes and record the temperatures of both jars. You may continue your observations every 5 minutes up to one hour.
- Your data table may look like this:
Time in oven (minutes) Temperature of
0 (initial temperature) 21ºC 21ºC 5 10 15 …
Make a graph: Use the above table to draw a line graph. Use blue color graph for fresh water and red color graph for salt water.
- If you have access to the hot sunlight, you may place both jars on a black background under the sunlight. A black background for the jars or painting the jars with black paint contributes to absorbing heat energy from the sunlight. If you use the sunlight, you may need to continue your observations and recordings for 3 or 4 hours. If the sunlight is not hot, this experiment will not work.
- You may do this experiment using sand instead of salt.
What is a control experiment?
Just to show that no other environmental factor caused the temperature increase, you may have a separate identical setup and do nothing with that. For example another pair of jars with fresh water and salt water that you don’t place it in the oven; however you measure and record their temperature. This will be your control experiment.
After you remove both jars from the oven, you can also observe and record the temperature drop every 5 minutes. Find out which one cools off faster.
Heat Retention and Dissipation Experiment
1. Poke a small hole in the cooler’s top. CAREFULLY insert one thermometer so it extends all the way through the top then about a centimeter. Tape the thermometer in place with clear tape. Be careful not to move the thermometer around in the hole it made.
2. Place the cooler’s top on the cooler so it seals. Record the temperature inside the cooler after five minutes and write that temperature in your journal.
3. Fill one plastic bottle with hot tap water. Use the other thermometer to record the temperature of the water for five minutes. Write the final temperature in your journal.
4. Place the hot water bottle in the cooler. Record cooler’s temperature every two minutes for the first ten minutes then every ten minutes for five to 8 hour.
5. Prepare a graph that shows heat loss in the system over a day’s time.
6. Repeat the experiment with the same amount of hot salt water (Include as much salt as possible).
7. Repeat the experiment with the same amount (by weight) of dry sand.
Make your own Styrofoam cooler.
Many heat related experiments need an insulated box that does not exchange heat with outside environment. Often we use ready made Styrofoam cooler for this purpose, but you can also build one. About $1 Styrofoam sheet will be enough for a decent size cooler. You can also use this cooler as a part of your display.
From a sheet of Styrofoam, cut 4 pieces 5″ x 13″ each. (You will have to use a sharp and dangerous utility knife also known as box cutter, adult supervision required) Connect them to each other using wood glue. Use some nails or screws to hold the pieces together while glue is being dried. This will be the internal layer of your cooler. When the glue is dried you can remove the screws and prepare the second layer of Styrofoam.
For the second layer cut 4 pieces 6 3/4″ X 13″. Connect these pieces over the previous pieces so the seams of internal layer will be covered. again use temporary nails and screws to hold pieces together until the glue dries.
Now we should make a top and a bottom for our cooler. We start by cutting two small squares of 4.25″ X 2.25″. Then we cut two larger squares of 7.25″ X 7.25 or larger.
Mount each small square in the middle of a large square and let it dry.
Later we glue one of these two to the bottom and keep the other for the top.
Finally the cooler is ready and we can start our tests by placing the first hot water bottle in the cooler to see how much heat does the hot water transfer to the environment.
Materials and Equipment:
- 2 glass jars
- Room-temperature water
- Hot water
- Two thermometers (MiniScience.com part number GATW-1 or GATY-1)
- Some 2″ nails
- Rubber band
- Clear tape
- Styrofoam ice chest (cooler) or Styrofoam boards (from hardware stores)
Results of Experiment (Observation):
Among the material that you tested (Water, Salt water and Sand), the one that has a higher heat retention will hold more heat in itself. For example 2 pounds water may hold more heat than 2 pounds of salt water or two pounds of sand. Any of these three that holds more heat, will make our Styrofoam box warmer and for a longer time.
For the heat uptake experiment you may calculate the rate at which heat was gained in Part A.(X degrees every Y minutes)
For the heat dissipation experiment you may calculate the rate at which heat was lost in part.
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.
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.
Explain how a solar heat collection panel works
|Gain (+), Loss(-)|
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.
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.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
Books related to physics, heat transfer and energy can be used as additional references.