Lesson Outline / Topics

DAY ONE

Lesson Objectives:

By the end of this lesson, you should be able to:

• Identify common driver behaviors that lead to wasted fuel and increased exhaust emissions.

• Describe why speeding up quickly from a stop wastes fuel.

• Describe why flat tires create more friction with the road than inflated tires.

Lesson Essential Questions:

1. How can individuals reduce automotive fuel consumption?

2. How do gear ratios determine the fuel economy of a car?

3. What is the relationship between friction and fuel economy?

Key Vocabulary:

gear ratio, rolling resistance, drag

Resources from other Web sites:

• http://fueleconomy.gov/feg/driveHabits.shtml – Driving More Efficiently

• http://fueleconomy.gov/feg/videos/Fuel_Economy_Tips.wmv – MotorWeek video

Class Discussion:

Using hands-on investigations, you will discover how driving habits can affect fuel efficiency. You will explore the concepts of drag and power and apply these concepts to driving habits that waste fuel. You will learn why driving faster uses more fuel, what effect “jackrabbit starts” have on fuel consumption, and how flat tires can waste energy.

Vehicle design is not the only feature that can lead to excess fuel usage. Driver behavior can waste more fuel than just having a large vehicle. Speeding up quickly from a start requires the vehicle to be in a low gear for a longer period of time, which requires more power. A poorly maintained engine can build up dirt that creates friction, which wastes power. Flat tires have more contact with the road than inflated

tires, causing more friction. Changing these behaviors and elements can decrease fuel usage and save money at little or no cost to the driver.

This lesson takes you through some simple physics ideas about drag, force, power, and energy use, using formulas and values to illustrate elements of vehicle efficiency.

We will discuss how gears are used to increase output by accessing the following website link: http://www.howstuffworks.com/gear.htm

Let's refer back to the previous lesson where you examined the relative fuel efficiency of different makes and models of vehicles. Relate it again to the whole concept of vehicle efficiency. Let's discuss whether a faster‐moving car is less efficient than a slower‐moving car. Back it up with evidence!

Think of ways that people waste gasoline that do not have to do with the design of the vehicle, recording the same within your Engineering Journal.

Student Activity 7:

Let us view the MotorWeek video (http://fueleconomy.gov/feg/videos/Fuel_Economy_Tips.wmv), which addresses both bad and good driving behaviors, and include additional information in their notebooks. This will help reinforce the lessons you learned in this class.

What did you find most interesting about the effects of bad driving behaviors on vehicle efficiency and fuel economy.

Class Discussion:

Engineers have studied the issue of vehicle efficiency and fuel economy. By using simple formulas, they can compare what happens with different vehicles in different driving situations. I caution you that these are simple comparisons and that formulas for vehicle design include many other factors such as road surface friction, motor type and vehicle mass. But for now, these are good formulas to start with to understand vehicle efficiency.

F_d = C_v²

This formula represents the effect that velocity has on air resistance, or drag. Fd is the force of drag, C is a coefficient that depends on the shape of the vehicle and the properties of the air, and v is the velocity of the vehicle.

Write the formula in your team journal along with a definition for each of the elements.

Student Activity 8:

The Department of Energy’s Find a Car Web site (http://www.fueleconomy.gov/feg/findacar.htm) from Lesson 1 has images of different models of vehicles. Let's take a look at different vehicles and determine which vehicle shape has the most drag or air resistance, which is represented by C in the equation.

Practice with the formula to determine what will happen to the amount of drag when the velocity is increased. What are some examples that will result in real numbers that you can try out. Additional values should help explain how much the velocity affects the force of the drag since the velocity is squared for every example.

P_d = C_v²

P_d represents the power needed to overcome air resistance. Please copy the equation into your team engineering journals and give an example of what you think each of the elements means. Specifically, I want you to relate power to vehicle fuel/energy sources such as those you learned about in Lesson 1.

Question: Regardless of the type of energy source, what would happen to the amount of power needed for a vehicle if the velocity is increased? Use several sample values to see how this works. If you provide a constant value for C you can create a simple graph of the data.

Class Discussion:

How much fuel/energy gets used is related to the amount of power used and the amount of drag on the vehicle. There are other factors that you will consider in future lessons, such as how much mass the vehicle is carrying. For now, let us demonstrate how this translates for one example vehicle.

Take a look at the following graph (http://www.fueleconomy.gov/feg/driveHabits.shtml) (Driving More Efficiently). This graph is a graph of speed versus fuel economy. Turn to a partner and discuss how the equations on the board are represented in the graph and discuss your thinking as a team. Note that many will see a discrepancy in this data versus what they expected. The drag and power formulas are simple representations, and from those students, would expect a continuous curve upward. This would be true except for another factor: the motor of the vehicle. In the vehicle represented in the graph, the motor actually reaches its most fuel efficient level at around 50 mph. What they should notice, however, is that once the vehicle gets past 55 mph, it begins to waste fuel.

Let us finish the discussion by asking ourselves at which speed a vehicle is most efficient. Although answers will vary according to the model of car, many vehicles are most efficient between 40 mph and 60 mph. Following the stated speed limits is one driving behavior that can save fuel. Driving the speed limit will keep a driver safer and save fuel.

DAY TWO

Class Discussion:

All vehicles use gears, although in automatic transmission cars, the vehicle changes gears instead of the driver doing it. As you will recall from our discussion about gears, we learned that gears transfer energy.

We will explore the concept of using gears to only transfer energy, but to also multiply the force that is used to turn the pedals of a bicycle. Please click on the following website link: http://adventure.howstuffworks.com/bicycle.htm

Student Activity 9:

In your teams and based on our discussion of bicycle gears, I want you to predict how switching gears will affect the power needed to spin the wheels. For example, which gear combination requires the most power and which requires the least energy. Which gears, lower or higher, cause the wheels to turn more slowly or faster. When the gear ratio is larger, what effect does it have on each pedal stroke and how it effect the turning of the back wheel (e.g., more or less).

After said discussion, update your engineering journals outlining said discussions.

Now that we have some notion of how gears work in bicycles, how do you think gears are used in automobiles. What kind of car do your parents use, one with a manual or automatic gearshift? Which gear do you requires the most power, based on yourr observations of a bicycle’s gear system. Hopefully, we will recognize that the lowest gears use the most power.

When a person driving an automatic transmission speeds up quickly from a stop, the vehicle does not have time to shift to a higher gear. How do you think this affects the amount of power that is required and , consequently, how it impacts fuel economy. How would it affect emissions output?

What affect do you think tire inflation has on fuel efficiency?

Factoid: If you determined that underinflated tires reduce fuel efficiency, you are correct. The main reason that underinflated tires reduce fuel economy is that an underinflated tire has more surface area touching the road, which provides more opportunities for the microscopic peaks on the tire’s surface to grip the road. This is called rolling resistance.

To understand the resistant force of friction, try moving you hand across your desk with only one finger touching the desk, then with all five fingers. What do are your conclusions? Write them in your engineering journal.

Now try running or jogging in place and describe your efficiency in terms of the ratio of the distance moved forward to the energy used. You should see that the efficiency is zero, since you did not move forward.

Given said realization, when is an automobile is running at zero efficiency. If you came up with situations such as sitting in traffic, letting a car warm up, or sitting in line at a drive‐through restaurant, you are correct.

Factoid: Let us focus on letting a car warm up. There is a common misconception that it is more efficient to let a car warm up in the winter because the engine runs more efficiently, especially when you consider that modern car engines do not need to warm up, and that this idling simply wastes fuel.

Is fuel efficiency a result of the vehicle’s design or of how the vehicle is driven?

List three driving behaviors that could be used to increase fuel economy at little or no cost to the driver and explain why those work.

Knowing what you now know, what factors would you consider when choosing a vehicle to drive if you have to pay for the fuel/energy it uses out of your own pocket? How would those factors be the same or different if you want to protect the environment?

Wrap‐Up:

We learned about how vehicle design as well as driver behaviors can increase or decrease fuel efficiency. In the next lesson we will discuss how other choices that drivers make can affect fuel efficiency.