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Science and Society

Transportation and the Environment
nvironmental science is an interdisci- Here is a list of things that people might QUESTIONS TO DISCUSS
Eplinary study of Earth’s environment. do to reduce the amount of environmental
The concern of this study is the overall damage from transportation: Discuss with your group the following
problem of human degradation of the en- A. Use a bike, carpool, walk, or take questions concerning connections between
vironment and remedies for that damage. public transportation whenever thought and feeling:
As an example of an environmental topic possible. 1. What are your positive or negative
of study, consider the damage that results feelings associated with each item in
from current human activities involving B. Combine trips to the store, mall, and the list?
the use of transportation. Researchers es- work, leaving the car parked whenever 2. Would your feelings be different if
timate that overall transportation activities possible. you had a better understanding of the
are responsible for about one-third of the C. Purchase hybrid electric or fuel cell– global problem?
total U.S. carbon emissions that are added powered cars or vehicles whenever
to the air every day. Carbon emissions are possible. 3. Do your feelings mean that you have
a problem because they are directly harm- D. Move to a planned community that reached a conclusion?
ful in the form of carbon monoxide. They makes the use of cars less necessary 4. What new items could be added to the
are also indirectly harmful because of the and less desirable. list?
contribution of carbon dioxide to possible
global warming and the consequences of
climate change.

So far, you have learned only about straight-line, uniform
acceleration that results in an increased velocity. There are also
other changes in the motion of an object that are associated 30 km/h 60 km/h 60 km/h 30 km/h
with acceleration. One of the more obvious is a change that
A Constant direction B Constant direction
results in a decreased velocity. Your car’s brakes, for example, increase speed decrease speed
can slow your car or bring it to a complete stop. This is negative
acceleration, which is sometimes called deceleration. Another 30 km/h 30 km/h
change in the motion of an object is a change of direction.
Velocity encompasses both the rate of motion and direction,
so a change of direction is an acceleration. The satellite mov-
ing with a constant speed in a circular orbit around Earth is
constantly changing its direction of movement. It is therefore
30 km/h 60 km/h
constantly accelerating because of this constant change in its
motion. Your automobile has three devices that could change C Change direction D Change direction
the state of its motion. Your automobile therefore has three constant speed change speed
accelerators—the gas pedal (which can increase the magnitude FIGURE 2.6 Four different ways (A–D) to accelerate a car.

of velocity), the brakes (which can decrease the magnitude of
velocity), and the steering wheel (which can change the direc-
tion of the velocity). (See Figure 2.6.) The important thing to
remember is that acceleration results from any change in the straight-line acceleration. To find an average velocity during a
motion of an object. uniform acceleration, you add the initial velocity and the final
The final velocity (v f ) and the initial velocity (v i ) are dif- velocity and divide by 2. This averaging can be done for a uni-
ferent variables than the average velocity (v) . You cannot use form acceleration that is increasing the velocity or for one that
an initial or final velocity for an average velocity. You may, is decreasing the velocity. In symbols,
however, calculate an average velocity (v) from the other two _

variables as long as the acceleration taking place between the v = v f + v i
2
initial and final velocities is uniform. An example of such a
uniform change would be an automobile during a constant, equation 2.3
2-7 CHAPTER 2 Motion 31