Once students’ misconceptions
about gravity and objects spinning in
space were uncovered, each group was
able to use its discussion and consideration of the new data to come to more
accurate explanations. Students took
responsibility for mediating the discussions. Occasionally, when a group
wasn’t quite there yet, I’d drop in and
engage one group member in this kind
TEACHER: I heard you say something
interesting about the planets and stars.
Would you be willing to share it with
STUDENT: Sure. I was positive that the
planets would get faster the farther they
got from the sun, but they didn’t.
TEACHER: Why did you think that?
STUDENT: Because we learned in physics
that a ball at the end of a string spins
faster and faster the longer the string is.
TEACHER: Let me see if I understand
what you’re saying. Let’s think of a DVD
spinning around inside a DVD player.
You’re saying that the part of the DVD
closest to the center spins slower than
the part of the DVD that’s near the edge?
STUDENT: Yeah. But that’s not what the
planets did. They got slower as they got
farther away from the sun.
TEACHER: What could explain that?
STUDENT: I don’t know.
TEACHER: What formula do we have
that explains how matter behaves
STUDENT: The law of universal gravitation. Oh! The planets get farther and
farther away from the sun, so gravity
TEACHER: Why isn’t that the same as the
STUDENT: Because the DVD is one solid
thing, but the planets are all separate.
At no point did I need to give away
Getting to Powerful Questions
answers: I only needed to ask pre-
dictive questions, provide data for
students to analyze, and ask students
to expand on their thinking by talking
within their groups.
Predictive questioning with strategic
discourse is especially powerful when
students hold firm misconceptions.
Every year in my physics class, I have
students who swear that shooting a
marble straight up in the air before it
lands on a runway will cause it to go
the farthest down that runway. It isn’t
until the marble hits them on the head,
and they answer a few pointed ques-
tions, that they realize that shooting an
object straight up only gives it height,
not distance. If I simply told them this
would happen, it wouldn’t have nearly
Any well-structured, inquiry-based
lesson is rooted in careful questioning.
Like Carnac the Magnificent on the
old Johnny Carson show, effective
teachers can predict the most gen-
erative questions to ask—as well
as the answers students are most
Predict: What happens to the orbital
velocity of the planets as they get
farther and farther from the Sun?
Draw your prediction on the graph at right:
Explain: Why do you think this?
Explain your logic:
As the planet gets further from the sun the velocity of the planet gets faster because it’s like a string tied
to a ball, the outside of the string gets faster, or moves faster. The planets have more mass so more gravity
is on them.
Observe: Look at the actual orbital velocities of planets as they get farther
and farther from the sun. Draw your revised orbital velocity curve on the graph
Revise: Revise your explanation
in light of this new evidence.
Gravity doesn’t work like a string because the string is all one thing so all of the string has to make it around
in the same amount of time no matter how far from the center it is. So the outside is faster than the inside.
But planets’ speeds work by gravity, and the further away from the Sun, the weaker gravity is so they slow
down. Some planets do have more mass, which is a direct relationship to gravity, but distance is way more
important because it’s inverse squared. So they get slower when they are further away.
FIGURE 1. Sample Student Work in First Part of Lesson on Dark Matter
F=G m1m2 r2