SAT Practice 1:
Mapping What the SAT Critical Reading Is All
About
170 MCGRAW-HILL’S SAT
demonstrated that pions carry the nuclear
force only over distances greater than half a
fermi—the radius of a proton—yet the
50 distance between bound protons is far less
than that. The pion seemed to be a giant
plumber’s wrench trying to do a tweezer’s job.
In the years since, physicists have refined
Yukawa’s theory to suggest that closely
55 bound protons or neutrons are held by a
“residual” force left over from the strong
forces binding quarks together into protons
and neutrons, so that pions don’t need to be
exchanged. If the protons and neutrons are
60 far enough apart within the nucleus, however,
perhaps pions do the job.- Which of the following best summarizes the
“paradox” mentioned in line 1?
(A) Teachers don’t utilize educational materials
effectively.
(B) A law of physics appears to be violated.
(C) Scientists continue to test hypotheses that
they suspect are false.
(D) Hideki Yukawa’s theory is incorrect.
(E) Scientists are increasingly reluctant to ex-
plore the difficult field of nuclear physics. - In lines 3–4, the author uses the term “vast knowl-
edge” in order to
(A) emphasize the daunting task faced by sci-
ence teachers
(B) empathize with overburdened students
(C) draw a contrast to an area of relative
ignorance
(D) praise the productivity of physicists relative
to other scientists
(E) acknowledge the difficulty of writing physics
textbooks
The following is an essay regarding current
knowledge of subatomic physics.A tantalizing paradox peers out from every
basic physics textbook, but rarely do students
Line notice it or teachers exploit it. Despite the vast
knowledge that scientists have accumulated
5 about the subatomic realm, including aston-
ishingly accurate equations for predicting the
behavior of barely detectable particles, an ob-
vious conundrum persists that they are only
recently beginning to understand: protons
10 stick together in atomic nuclei.
All first-year physics students learn that the
atomic nucleus contains neutrons, which have
no charge, and protons, which are positively
charged. They also learn that while opposite
15 charges attract, all like charges repel each
other, just like the north poles of two magnets.
So what keeps all of those positively charged
protons bound together in a nucleus? Physi-
cists have long postulated that there must be
20 another special force, called the nuclear force,
that counteracts the electrical repulsion be-
tween protons. But where does it come from?
One theory, proposed by Nobel laureate
Hideki Yukawa in the 1930s, held that the nu-
25 clear force is conveyed by a particle called a
pion, which, he claimed, is exchanged among
the neutrons and protons in the nucleus.
Forty years later, physicists discovered that
pions, not to mention the protons and neu-
30 trons themselves, are actually composed of yet
smaller particles called “quarks,” which are
held together by aptly named “gluons.” The
force conveyed by gluons is called the “strong”
force. Although experiments had clearly
35 demonstrated that these gluons are responsi-
ble for the force that binds quarks within pro-
tons and neutrons, nothing suggested that
gluons are exchanged between protons and
neutrons. Nevertheless, by the early 1980s,
40 most physicists became convinced that some
combination of gluons and quarks, perhaps the
pion, must be responsible for the nuclear force.
Professor Yukawa’s theory, however, was
dealt a blow by a series of experiments that
45 were conducted at Los Alamos National Labo-
ratory in the early 1990s. These experiments© 2004 Christopher Black. All rights reserved. Reprinted by per-
mission of the author.