1. Students will be able to explain the relationship between the amount of air pressure in car tires and their fuel efficiency.
2. Students will be able to provide an explanation for the ability of synthetic fuels to increase fuel efficiency.
3. Students will gain understanding of the role which air resistance plays in the fuel efficiency of vehicles.
The science portion of this interdisciplinary unit focuses on providing students with some first-hand experience with three different factors affecting fuel efficiency. Students will be involved in activities designed to illustrate the changing viscosity of motor oil at different temperatures. In addition, students simulate the effects of driving with underinflated tires on vehicle speed and fuel efficiency. Finally, students investigate the role of air resistance on fuel efficiency. They put their new knowledge to work by developing an aerodynamically designed school bus.
Middle school students most definitely have driving on their minds. Many middle school students will have or will soon be getting driving permits. Some may have already taken driver education courses. This is a good age to impress upon students the huge role which transportation plays in energy consumption in Iowa. It is equally important that students realize they can play an active role in conserving fuel. Most students will think this means they have to drive less. But there are lots of ways to increase the fuel efficiency of a vehicle. Impress upon students that they may be learning some things their parents do. Remind students that they should do their part in helping conserve fuel by simply giving the drivers in their families some advice on how to make fuel-wise choices.
The three activities in the science portion of this unit are written with specific suggestions to the teacher on how to successfully implement the activity. It will be important for you to set the tone of the unit by introducing each activity and by providing time for discussion following the gathering of data.
Teacher Notes
Objective:
By completing this activity, students will observe how friction changes with the pressure in an inflated ball. This example will then be applied to the desired tire pressure in an automobile.
Materials:
basketballs (one per group)
meter sticks or tape measure
tire pump with needle for inflating balls
large rubber bands (if students choose sling-shot approach)
ramp (if students choose this approach)
tape or chalk
stop watch
Article entitled "A High-Pressure Way to Get There Cheaper" (Appendix A)
Overhead of Research Question
Teaching Strategies:
Students may not realize it, but the pressure in a car's tires plays a big role
in fuel efficiency. In this activity, students will discover the relationship between tire pressure and fuel efficiency. Rather than using an actual car, the situation can be simulated using a ball.
Place a copy of the research question on the overhead or chalkboard:
Research Question
How does the amount of air pressure in a ball affect its speed when rolled across the floor?
If time permits, it would be desirable for students to set up their own experimental design for answering this question. The degree of direction you wish to provide will be up to you and will be dependent upon the expertise of your class in controlling variables. The paragraphs that follow contain one possible approach to organizing this activity.
Hold up a ball and tell students they will be using balls like this one to find the answer to the research question. Also show students a bike tire pump and show them how you can add air to the ball. Unscrew the needle. Insert it into the ball and show students how air can be removed from the tire. Ask for their ideas on how they might go about collecting data. There are a number of variables that must be controlled. Throughout the discussion, as students share their ideas, be sure to question their control of variables along the way. In this manner, the class is likely to devise a relatively controlled experiment that will provide sufficient data to answer the question.
A sample design might go as follows: (You may wish to simply provide students with the directions below if time does not allow you the opportunity for class discussion of experimental design.)
1. Use a meter stick or tape measure to mark off a straight distance of 10 meters. Mark the start and end points with tape or chalk.
2. Unscrew the needle of a tire pump. Push the needle into the ball and release enough air to allow the ball to still roll, but with some difficulty.
3. Prepare a rubber band sling shot by tying several rubber bands together. While your partners hold the sides of the sling shot, pull the ball back with the stretched rubber band.
4. Mark the exact point at which the ball is released, so that it may be released from this same spot for each trial. Using the stop watch, determine the amount of time it takes when the ball is released until it crosses the finish line. Do several trials and average your results.
5. Now repeat the same procedure, but inflate the ball by two pump strokes. Record the results of several trials and determine the average time required to cross the finish line.
6. Add two more pump strokes of air and repeat the procedure. Keep testing different inflation levels until the air pressure indicates the ball is "full."
NOTE: Another possible approach to testing the ball is to use the same inflation process, but to roll the ball down a ramp. If this approach is tried, suggest that students use a low enough slope to allow the ball to move slowly down the ramp. This will allow students to observe a larger difference in the rolling speeds of the ball.
Sample Answers to Summing Up:
1. Students should have data supporting the conclusion that the lower the air pressure, the slower the ball moves. With higher air pressure, the ball should roll faster.
2. Students will likely conclude that the fuel efficiency will improve as tire pressure increases. This is true because tires low on air pressure will have greater friction between the pavement and the tires, causing an increased drag on the car.
3. Student plans will vary. Encourage creativity in student writing. Insist that students include a logical rational for driving with the correct tire pressure.
Discussion:
After discussing student findings and their answers to the first two Summing Up questions, ask students to read the article entitled "A High Pressure Way to
Get There Cheaper", Appendix A). Then ask students if they know how often the tire pressure is checked on their family vehicle. How many know if they have a tire gauge at home? Encourage students to find out and to share what they have learned with their parents.
Home/Community Connection:
Extensions:
Student Page
Problem:
Find out how the amount of air pressure in a ball affects its rolling speed.
Materials:
meter stick
basketball
tire pump
stop watch
chalk or tape
other things you may need depending on the design of your experiment
Let's Investigate:
In this activity, your job is to discover the answer to the following question.
Research Question
How does the amount of air pressure in a ball affect its speed when rolled across the floor?
We call this a research question, because you will need to conduct your own research to discover the answer. Your teacher may give you a few hints about how to control variables in your experiment. However, the main design for the experiment is your job. Not everyone will come up with the same design. This is good. There is no one right way to answer the research question. Lots of different experimental designs will help to answer the question.
Your first job is to discuss possible plans with your partners. Once your group has decided on a plan, make a list of the materials you will need for your experiment. Draw a picture of your experimental set-up. The picture should show how you will be collecting data. Describe the steps you will follow in collecting data for your experiment. To keep your thoughts straight, here are a few headings you should have on your paper.
Materials
Drawing of experimental set-up
Steps in our experiment
Once you have written down your ideas, ask your teacher to check your plan. Your teacher will then help you to gather the materials you will need to collect your data.
Use a table to collect your data. Label the first two columns with headings that fit your experimental design. It is always a good idea to perform an experiment more than one time. Notice that the third column should contain room for conducting three trials. You can then average your results, or even omit data that you can see is "way off".
Summing Up:
1 .Study your data. What is your conclusion about how the amount of air pressure in a ball affects its rolling speed?
2. Apply your findings to car tires. What affect do you think the air pressure in car tires has on fuel efficiency? Explain your answer.
3. Read the article entitled "A High-Pressure Way To Get There Cheaper". After you have completed the article, devise a plan to convince the drivers in your family of the importance of keeping the correct air pressure in their tires. Write a summary of your ideas. Be sure to include any reasons you might provide for wanting to drive with the correct amount of air in the tires.
Teacher Notes
Objective:
The purpose of this experiment is to discover how the viscosity of oil changes with temperature. This relationship plays a vital role in the efficient running of a car engine.
Materials:
sealed test tubes containing regular and synthetic oils
thermometers
refrigerator or cooler containing ice cubes
warm water baths (buckets of warm water will be fine)
stop watch or clock with second hand
overhead of Challenge Question
Teaching Strategies:
You will need to prepare a number of test tubes containing regular motor oil and a sample of synthetic oil, ahead of time. Mobil 1 would be a good synthetic oil
to use and is available at most auto and discount stores. Longer test tubes are preferred over shorter ones. Students will be timing how long it takes the oil to run from one end of the tube to another. They will observe a greater time
difference between the fast and slow flowing oil when using longer test tubes. A length of 15 cm works well. If you have longer tubes available, try them. If using shorter test tubes, experiment with the amount of oil added to each test
tube to determine which volume works best with a small test tube. Three to five cm of oil placed in a corked 15 cm test tube works well. Safety Warning: Even though the oil is sealed test tubes, do not have any open flames in your classroom at while carrying out this experiment.
You may wish to read the short article, "Oil That Works" shown in Appendix A, to students as a method of introducing this activity.
In this experiment students will try to discover what it is about synthetic oil that makes it so much better than regular motor oil.
A short synopsis of the student challenge is provided below.
The Challenge
You are to test how the speed of "flow" for two different oils changes at different temperatures. Design your own experiment to show how the flow-ability of each oil is affected by different temperatures. Warm water baths and cold water baths are available for you to use. Your big restriction is that you are
not to unseal the test tubes containing the oil. With this in mind, get together with your partners to set up a plan that will allow you to determine the affect of temperature on oil flow-ability.
You may be surprised at the different ideas students use in determining oil flow-ability. Some students will likely suggest marking the side of the test tube by centimeters. Students could tip the cooled or warmed test tube and time how long it takes for a certain number of centimeters to flow from one end to the other. There is no one correct way to do this. Encourage creativity, allowing time after the data has been collected to discuss how the data was gathered.
Sample Answers to Summing Up Questions:
1. The synthetic motor oil should flow the fastest under warm conditions, although the oils are fairly similar at warm temperatures. Many students will likely get similar results for both the oils under warm conditions.
2. The synthetic oil will also flow the fastest under cold conditions.
3. Students should come to the conclusion that the synthetic oil would be best for your car in winter months. This is true because the synthetic oils remains pretty runny at cold temperatures. This means that it can still circulate in your engine to those parts in need of lubrication. If the oil was thick, it would be slower in reaching all parts of your engine.
Home/Community Connection:
Extensions:
Find out what the weight numbers mean on oil labels. Design an experiment to discover the relationship between oil weight and viscosity.
Student Page
Problem:
Find out how the thickness of oil changes with temperature.
Materials:
sealed tubes containing regular and synthetic oils
thermometer
hot and cold water baths
stop watch or other timer
Let's Investigate:
Your challenge is to test how the speed of "flow" for two different oils changes at different temperatures. Design your own experiment to show how the "flow-ability" of each oil is affected by different temperatures. Warm water
baths and cold water baths are available for you to use. Your big restriction is that you are not to unseal the test tubes containing the oil. With this in mind, get together with your partners to set up a plan that will allow you to determine the effect of temperature on oil flow-ability.
Before beginning to collect data, write a few sentences describing how you will compare the flow-ability of the two types of oil.
Place a heading in the first column of a data table on the next page. Use the table to record all of your findings.
Summing Up Questions:
1. Which type of motor oil flowed faster under warm conditions?
2. Which type of motor oil flowed faster under cold conditions?
3. Much of the wear and tear on a car engine occurs during the first few minutes after the car is started. When all of the moving parts of the engine are well oiled, they run smoothly and efficiently. But in order to reach all the moving parts, the oil must move throughout the engine's moving parts when the engine is started. If it gets too thick, it won't get to the moving parts right away. Using these ideas, explain whether one of the oils tested would be better for your car in winter months than the other. Be sure to use your data about the flow-ability of the oils at different temperatures in answering this question.
Teacher Notes
Objective:
The purpose of this activity is for students to discover the relationship between the shape of an object and the air resistance (aerodynamics) of that
object. Students will then relate their findings to the shapes of automobiles and their resulting fuel efficiency.
Materials: (one per student group)
stop watch or clock with a second hand
plasticine or modeling clay (about 24 grams per student group)
graduated cylinder or other tall tube
fishing line or other lightweight monofilament line
counterweight (sinker, washer, clay, etc.)
Background:
Drag is the resistance any object feels while moving through the air. If you hold your hand out the window of a moving car, drag is the wind resistance
pushing it back. Nearly 60% of the fuel a car uses to drive at a constant 55 mph goes into overcoming wind resistance. So reducing a car's drag can greatly improve its gas mileage (miles per gallon).
The "Cd" or Coefficient of drag, measures how well a shape cuts the wind. It can be calculated for any object from a brick to a blimp. The lower the Cd, the more aerodynamic the shape. For cars and trucks, a low Cd translates directly into better gas mileage. A drop in the average Cd of all road vehicles in the U.S. from 0.4 to 0.3 could reduce the nation's gasoline consumption by 10 percent. This would add up to a yearly savings of over 10 billion gallons of gasoline.
Many students may not realize it, but air is a fluid. A fluid can be a liquid or a gas. It is typically considered anything that can flow and which responds to changes in pressure. Because of its fluid properties, water can be used to illustrate the amount of drag objects have when passing through a fluid. An object that has low drag when moving through air will also have a low drag when it is moved through water. Keep reminding students of this as they are collecting their drag data using water.
Suggested Teaching Strategies:
The fuel efficiency of cars would be greatly increased if air resistance could be reduced. Many students have likely held their hand out the car window while
riding. You can feel your hand getting pushed back. This is largely the result of air resistance.
The greater the air resistance, the more fuel it takes to move a car. Race cars are built with sleek designs. This allows them to go faster on less fuel. But these cars do not have much extra room inside. They are not designed to carry passengers or other items. The challenge is to discover the relationship between the shape of an object and its speed through a fluid. To discover this the speed of objects will be measured through water, since it is easier to notice differences in speed through a liquid than it is through a mixture of gases like air. Be sure students realize that their findings in water will be analogous to what would happen to the object's speed as it travels through air. Air is considered a fluid. Be sure to communicate this to students. Present students with this challenge:
Challenge
How does the shape of an object affect its speed through water?
Ask students to brainstorm possible shapes to test. Most students will likely name shapes such as a cone, a square, a sphere, an oval, a wedge and a torpedo. Ask students to predict which shapes will fall fastest through the water. Rather than explaining the lab set-up to students, it may be easier to demonstrate the technique. Do so by creating a shape out of clay. Push one end of a piece of fishing line through the shape, securing it with a knot. Show students how fast the shape drops through the water when it is dropped into a filled graduated cylinder. Now attach a counter weight to the other end of the string. This will serve to slow down the clay as it drops through the water. Ask students if they think this is a fair test of how fast the clay drops. Hopefully students will realize that it is Okay to use the counterweight as long as it is used for every trial. Likewise, when the shape of the clay is altered, the same clay lump should be used. This will ensure that the shape, not the mass is the only factor being varied in this experiment.
Using a stop watch, record the time it takes for the object to fall through the water. Continue testing until three consistent trials have occurred. Ask students to devise their own data tables for recording their data.
Before allowing students to investigate different shapes on their own, ask students how they can best control as many variables as possible in their experiment. Some suggestions might include always using the same line, drying off the line after each trial, always using the same lump of clay, performing several trials for each shape, and having the same person run the timer each trial and the same person release the clay each time.
Once students have collected their own data, ask them to answer the Summing Up questions shown on the student page.
Sample Answers to Summing Up Questions:
1. Students should find the shapes to fall from fastest to slowest in this order....torpedo, cone, wedge, sphere, and cube.
2. The more aerodynamic the vehicle, the less gasoline it takes to move the vehicle.
Home/Community Connection:
Visit a local car dealership. Ask to examine the new car brochures. Make a list of the special aerodynamic design features of the new cars. Many auto
makers list the coefficient of drag under each car's specifications. Look for these figures and make a comparison between the Cd value and the size of the car. Report your findings back to the class. Some students might want to prepare a bulletin board display containing pictures of various cars and their
Cd values. Perhaps the bulletin board could be designed as a guessing game, where those looking at the board had to guess which cars had the lowest drag and which had the highest drag values.
Extensions:
Challenge students to draw lines to represent the air current passing over each of the objects shown below. Rate the objects from the one with the largest drag to the object with the least drag.
Here are the actual findings
Some students might enjoy testing resistance in a home-made wind tunnel. To make a wind tunnel, students will need the following items:
large box (computer size, approximately 1 cubic meter)
rubber bands
shapes to be tested (styrofoam works best)
window (box) fan
ruler
knife for cutting cardboard
The drawing below illustrates how to prepare the wind tunnel.
Click here to get the drawing
of the wind tunnel
To test different shapes, turn on the fan. Looking through the window in the box, measure how far the object moves into the box when the fan is turned on. You will be surprised how well this simple design works. Students will need to make certain that the mass of their test objects is about the same. Remind them to control as many variables as possible.
Student Page
Problem:
Discover the relationship between the shape of an object and the air resistance (aerodynamics) of that object.
Materials:
stop watch or clock with a second hand
plasticine or modeling clay
graduated cylinder
fishing line
counterweight (sinker, washer, etc.)
Let's Investigate:
The fuel efficiency of cars would be greatly increased if air resistance could be reduced. The greater the air resistance, the more fuel it takes to move a
car. In this activity, your challenge is to determine which shapes have the most air resistance and which have the least air resistance. You will be using water instead of air to measure resistance. This is a useful thing to do since
water will slow down the different shapes enough to allow you to measure the time difference. Water and air are both fluids, so the results will be the same. The shape that has the most resistance when moving through water will
also have the most resistance as it moves through air.
Think about the different shapes you could test. Keep in mind that you want to relate your findings to the shapes of cars. Draw the different shapes you wish to test. Once your drawings are completed, make a prediction as to which will have the most air resistance and which will have the least.
Your teacher will go over the procedure for testing the aerodynamics of different shapes. Gather all of the materials and practice a few times, before you begin recording data. Once you have gotten good at timing the sinking, begin collecting data on the different shapes. Record your data in a table. Remember to control as many variables as you can.
Summing Up Questions:
1. Which shapes had the least amount of drag and which had the most drag?
2. Explain how the aerodynamics of a car relates to its fuel efficiency?
Teacher Notes
Objectives:
Students will be able to identify structures of a typical school bus that have high air resistance and will be able to suggest alternative structures with lower air resistance.
Materials:
paper
drawing supplies
Background:
There are two kinds of air resistance (drag) that are important in car design. Form drag occurs when airflow breaks away completely from the car's surface.
Mirrors, fenders, hood ornaments and other features that stick out from the car's surface all cause the air to swirl around them. This swirling air saps energy from the moving car, slowing it down.
Friction drag acts along the surface of a car. Air moves over a hood causing winds to build in thin layers. The layer closest to the car's surface moves the slowest. Other layers of airflow slide over this slow boundary layer causing friction. It requires extra energy to overcome this friction.
Suggested Teaching Strategies:
Begin by explaining to students the two types of drag explained in the
Background section. It will be the form drag which plays the largest role in reducing fuel efficiency in vehicles.
Ask students to hypothesize about the relationship between the amount of drag on a vehicle and its fuel consumption. (The lower the drag the less fuel consumption.) With this in mind, challenge students to create a design for a new style school bus. The challenge is outlined on the student page. Once students have made their designs on paper, you may wish to challenge students to build a model of their bus. The model could be made from cardboard and would not need to be a working model (in terms of actually rolling).
Sample Answers to Summing Up Questions:
1. Once students have completed their drawings, ask the students to present their designs to the class. Ask each student to include mention of the low drag features as part of their presentation.
2. After listening to all of the ideas of their classmates, ask for suggestions for a "super bus". If students pool the best ideas from everyone, they should be able to make a truly unique design.
Extensions:
Home/Community Connection:
Challenge students to go out to the parking lot and find the five most aerodynamically designed cars and the five least aerodynamic vehicles. Ask
students to design their own checklist with an appropriate rating scale. Include a brief explanation of the important aerodynamic features written so the general public can easily understand it. Give the completed checklist to the car owners.
Student Page
Problem:
Identify structures of a typical school bus that have high air resistance and suggest alternative structures with lower air resistance.
Materials:
paper
drawing supplies
Let's Investigate:
Here in Iowa, a great deal of energy is used each year transporting students to and from school by bus. Students also make many trips each year by school bus
for athletic events and other school-related events. Just think about all of the energy and money that could be saved each year, if school buses could use energy more efficiently. One way to increase fuel efficiency would be to
redesign school buses to be more aerodynamic. This is where your challenge comes in. Your challenge is to design a new style school bus. The bus should be designed to save fuel due to its special low-drag features.
One way to approach this task is to think about those structures on a typical bus that stick out from the car, increasing air resistance. These would be good targets for reducing air resistance. Think about different ways and places to attach license plate numbers, headlights, windows and side mirrors. Don't be afraid to come up with a totally new look. Since you do not need to worry about details such as the material of which the body is composed or the size of the engine, you can concentrate on an innovative design. Don't be afraid to try something new!
The bus must conform to these guidelines:
Guidelines for Low Resistance School Bus
Summing Up:
1. Make a list of the special low drag features of your bus. Present your design to the class. Be sure to point out the low drag features as part of your presentation.
2. While listening to all of the ideas of their classmates, pool your favorite ideas for a "super bus". Make a drawing of this revised bus.
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