Tim Langford, Teacher
Please respond to this article by email directly to me or the editor, Roberta Tevlin, at firstname.lastname@example.org. We need an ongoing discussion of this topic, since language is at the heart of education, and not just in physics.
The problems I mention in this article are not always major, but they seem to have an asymmetrical effect: it is mainly the weaker physics students, in my experience, who are thrown off by confusing or vague terminology or the teacher misspeaking. This anecdotal finding is corroborated by Hammer’s (1989) research with undergraduate physics students. There is also another issue: careless language leads to careless thinking, a type of thinking that will not get the student very far in the study of physics.
The ubiquity of many of these problems only came to light when I started letting my students do most of the talking. This happened about six years ago when I started following Chris Meyer’s reformed physics program that uses guided inquiry in cooperative small groups. Listening to the students’ conversations with each is powerful way to uncover their misunderstandings. Most of the problems I present here are very specific and I suggest attendant solutions. However, I would like to begin with some general solutions or “best practices” for two-way communication in the physics classroom:
- Think like a journalist: avoid technical terms where possible, and define any terms that you even suspect might be new to your students.
- Provide diagrams, pictures, video, or live demonstration to accompany the text of questions.
- Encourage student questions at any time, including on tests, to clarify language and its meaning.
Everyday WordsReading level:
Five years ago I would not have suspected that words like “gradually” and “ceased” would be unknown to some of my students, and yet they are. We should use words like “slowly” and “stopped”. The best practice here is to teach students that if any word or phrase is blocking their understanding they have a responsibility to ask or to look it up. Urbanization:
Some students in the GTA have rarely been outside of the city. While I defined terms like “airspeed” and “groundspeed” for airplane problems, it hadn’t occurred to me until I taught these students that I needed to define “upstream” and “downstream” for boat problems. (Perhaps urbanization is not the problem, though: the word “overpass” turned out to be unknown to many of my students, too.)Cultural Bias:
There are many examples of this, but I will mention only one area of cultural bias: sports. Soccer is the world’s most popular sport, yet I, like the textbooks, traditionally used problems taken from baseball, football, and golf. I now realize that these are sports many students have never played or watched, leaving them in the dark when a term like “line of scrimmage” or “home run” is used. Some students don’t follow sports at all. This shouldn’t keep us from using sports examples any more than we should shy away from using examples from music or house wiring or any other experience that the students may not have had. What I believe we need to do is to provide students with visual aids (photos, video) that help them get a mental picture of the situation and the action. Recently I wrote a test question about Evel Kneivel’s historic jump over Mack trucks completed successfully at Toronto’s old Exhibition Stadium in the early 1970s. I showed a video of the jump on a repeating loop during the test, since most students had no experience with this kind of daredevil act. Please respond with your examples of everyday words or terms that have given your students trouble.
Some words used commonly in physics classes are loaded with multiple hidden meanings or connotations, known to physics experts, but which need to be “unpacked” for the physics novices we teach. “Motion”
Consider the following sample question:
“Describe the motion of a ball as it rolls up a ramp and back down again.”
Prior to instruction students will write a variety of answers, such as:
- “The ball rolls up, stops, and rolls back down.”
- “The ball has decreasing motion on the way up and increasing motion on the way down.”
- “The ball slows down on the way up and speeds up on the way down.”
After instruction the students will do better. The teacher will have “unpacked” the word “motion” for them, making it clear that they need to describe the velocity of the ball, and perhaps its acceleration, at each of several key positions. This is a case where a picture is worth a thousand words, or at least a few dozen. An improved version of the question might include a labelled diagram and the phrasing“Describe the velocity and acceleration of a ball at each of the five positions A, B, C, D and E as it rolls up a ramp to its highest point, C, and back down to point E, which is the same position as point A.”
The teacher will likely need to unpack the word “motion” for every future occurrence of a question with the word “motion” in it. Solution:
Ban the word “motion” altogether. Stick with the terms that are its baggage: position, velocity, and acceleration. Related problems:
The problem with the word “motion” is further confounded by the existence of two synonymous terms, “uniform motion” and “constant velocity”. Students tend to conflate these to generate their own meaningless new term, “constant motion”. Again, this is a problem that is easily solved by banning of the word “motion” altogether. Coin your own new term, “uniform velocity”, and use this term consistently.
Students sometimes combine the word “motion” with a change word like “increasing” or “decreasing”. Example: "The motion increases at a constant steady velocity in the positive direction”. Here the student is attempting to describe uniform velocity, but is perhaps also wondering about how the object got to that velocity from a state of rest (having not yet “bought into” Newton’s First Law). The revised versions, depending on what the student was trying to say, are:“The object moves with uniform velocity in the positive direction.”
OR“The object starts at rest, speeds up in the positive direction, then moves with uniform velocity.”
Even without the word “motion” involved, students will sometimes make up confusing phrases like “Slowing down in the negative direction” or “Getting faster in the negative direction”. Again, we must be vigilant here in insisting that the students give the direction of both the velocity and the acceleration. “Seconds squared”
I know what you’re thinking: this is not a term I have ever used in class. However, every time we refer to acceleration we use this concatenation of words. So the question that must occur to students is, “What the heck is a second squared? How can you square time?”Problem:
the unit m/s2
lacks physical meaningSolution:
“Unpack” the units of acceleration for students by explaining, “The object speeds up (or slows down) by x m/s every second.” Repeat this daily for the first week of kinematics.Please respond with your examples of loaded words or terms that have given your students trouble.
Vague or Confusing Words“Decelerate”
I was not even convinced this was a word until I checked Onelook.com and found that most dictionaries do list it. The commonly given definition is “to slow down”. Problem:
Students tend to use this word whenever the acceleration is negative. This is not always a situation of slowing down! Solution:
Ban this word. Train the students to use the simple, everyday terms: speeding up, slowing down. They must also give the direction of the motion, of course.Example 1:
Student: “The car is decelerating”.
Revised version: “The car is moving forward and slowing down.”Example 2:
Student: “The bus is decelerating.”
Revised version: “The bus is moving backwards and speeding up.”“Gravity”
Have your students answer the multiple choice question below and do a tally.
In physics, the word “gravity” refers to:
a) an acceleration
b) a field constant
c) a force
d) an energy
If you present this question to physics experts you will not get a convergence of opinion. Physicists will probably answer d), while high school physics teachers will mostly answer c). Most of your students will likely answer c), but there is evidence in the way they talk and write that they are not sure. How often have you heard a student say, “Gravity is 9.8” or seen a student write “Fg
= 9.8 N”? Problem:
The word “gravity” is too vague, referring perhaps to a force, perhaps a field, or even an acceleration. Students are unclear what they are talking about when they use this word.Solution:
Ban the one-word phrase “gravity”. Insist the students use either “force of gravity” or “gravitational force” when writing or talking about this force. Insist they use “acceleration due to gravity” if this is what they are talking about. Teach them when to use “gravitational field constant” instead of “acceleration due to gravity”. I teach students not to use m/s2
as the unit for g
unless they are dealing with a projectile. I insist on N/kg and remind them that g
in this case is called the “gravitational field constant”.“Weightless”
We teach our grade 11 students that the definition of “weight” is “force of gravity on a mass”. It follows that no mass can be weightless anywhere near the Earth. Yet the word “weightless” is used frequently by astronauts, journalists, and some physics teachers. Imagine how confusing this is for students!Problem:
The problem is really the way in which we define weight.Solution:
We have three choices on this one:
Start teaching in grade 11 that “weight” means “the normal force”. We don’t feel gravity. What we perceive as weight and what we call weight, is just how we make sense of the normal force. Some forward-thinking physics teachers already do this.
Work with the current definition of weight and introduce the rather confusing term “apparent weight” as a synonym for “normal force”, after lots of instruction and activities to reinforce the idea we do not measure weight directly
Ban the word “weight”. Insist that the students use the terms “force of gravity” and “normal force”. Instead of “weightless”, then, we could use the term “normal forceless”. “Zero Gravity”
Don’t even get me started. This one is even worse than “weightless”. Every time I hear an astronaut use it in reference to experiences in orbit I want to scream. The associated term “microgravity” sounds more scientific but is also quite misleading. “Free Body Diagram”
This term is supposed to convey “a body free of its surroundings”, which is of very little help to the student. What it does not convey is what the diagram does show, namely, the forces acting on the body. Chris Meyer (perhaps not his innovation) has renamed this diagram a “force diagram”. The name conveys what the diagrams shows. The name becomes meaningful. I encourage you to train your students to draw Force Diagrams!“Inertia”
A quick survey of six dictionaries on Onelook.com reveals three that begin the definition of inertia with “the property of matter…”, two that begin the definition with “the tendency of a body…”, and one that actually begins the definition with “the physical force…”. This survey suggests that there is little agreement about what this term means. Students all-too-often choose the third of these definitions, the one that imbues inertia with the properties of a force. This is obviously very problematic.
Moreover, the word “inertia” could easily fit into my category of “loaded words” because it is essentially a one-word synonym for Newton’s First Law, with all that it entails. (I am sure that I don’t need to tell you!) Then there is the issue of the word “mass”, which, if properly defined (eschew the grade 10 definition referring to “the amount of matter in a body”) yields a definition that is remarkably similar to the one given for the word “inertia”. Problem:
The word “inertia” has no clear agreed-upon definition, but appears to be used both as a synonym for Newton’s First Law and a synonym for mass. Solution:
Ban the word “inertia”. Stick with the word “mass”, and do a full unpacking of the loaded term “Newton’s First Law”. “Cancels out”
This is a term that students love and that math teachers have been trying to stamp out for generations. We need to help those math teachers! Student assertions like “The normal force cancels out the force of gravity” imply that these two forces annul each other and cease to exist. It is extremely misleading and inappropriate talk that needs to be shut down as soon as it rears its ugly head. Please respond with your examples of words or terms that are vague or confusing to your students.
Hammer, D. (1989). Two approaches to learning physics. In The Physics Teacher, Dec. 1989, pp.664-670. Retrieved online Dec. 1, 2015 from http://www.daubertphysics.us/wp-content/uploads/2010/08/Hammer_paper.pdf
Knight, R.D. (2002). Five Easy Lessons: Strategies for Successful Physics Teaching. Addison-Wesley, University of Michigan.