In this post, I put down the student misconceptions on kinematics that I came across from reading physics education research (PER) papers that have been published.
Kinematics means the study of motion. So, this post will focus on student difficulties on displacement, velocity, speed, and acceleration.
Definitions
Before I discuss what I learned from the research papers, let me put down the definitions for several physical quantities related to kinematics:
Position: The location of an object measured from a reference point.
Displacement: Change in position
Distance: Length between two points.
Average velocity: Displacement / Change in time
Instantaneous velocity: The value of average velocity at the limit when the change in time goes to zero.
Average speed: Distance traveled / Change in time
Instantaneous speed: Magnitude of instantaneous velocity
Average acceleration: Change in velocity / Change in time 
Instantaneous acceleration: The value of average acceleration at the limit when the change in time goes to zero.
I know that I have listed a lot, but they are important.
What I learned from the research papers?
Here are some papers that I have browsed:
- Investigation of student understanding of the concept of velocity in one dimension
- Investigation of student understanding of the concept of acceleration in one dimension
- Students’ preconceptions in introductory mechanics
- Common sense concepts about motion
The first two papers were written by David Trowbridge and Lillian McDermott. I am just going to pull out the main findings that are covered by them.
- Two objects travel at the same speed when they are side-by-side or vice versa.
- Students confuse between position and acceleration by comparing the objects’ accelerations using the relative positions.
- Students confuse between velocity and acceleration by comparing the objects’ accelerations using the final speeds.
- Students do not distinguish position and displacement, velocity and change in velocity. They write
or
instead of
or
.
The next paper was written by John Clement. He found that the most common students’ errors can be categorized as “motion implies a force” preconceptions. Since force is related to acceleration, I would link it as failure to distinguish velocity and acceleration.
This error can show up in two occasions. (1) Constant velocity motion – some students think that when objects move at constant velocity, the acceleration is in the same direction as the velocity. (2) Object moving up in vertical direction – while the object is moving up, some students think that there is an acceleration in the upward direction.
Halloun and Hestenes wrote the fourth paper. They summarized the common sense concepts students had about motion. Here are what they found:
- Students do not distinguish “time interval” or “instant of time.”
- Students tend to write
- Students do not distinguish distance, velocity, and acceleration.
My takeaway
Based on what was reported, the common errors students made usually involve confusion in the definitions of displacement, velocity, and acceleration.
To me, it is natural to get confused by those terms because it is a new topic to beginning students and it takes time for them to get used to the language and description used in physics. It took me 3-4 years to get better at distinguishing them.
Implications to teaching – overcome student misconceptions on kinematics
Learning activities need to get students to apply the definitions in different types of motions – constant velocity, speeding up and slowing down with constant acceleration.
It may be possible to incorporate motion sensors to teach kinematics. If the school can purchase a few sets, that will be a great tool to show students how measurements are performed and how the motion-graphs for different kinds of motion will look like. This will give students a better idea of what physicists meant by position, displacement, velocity, and acceleration.
Implications to learning – overcome student misconceptions on kinematics
If you are a student who came across this article, I want to say it’s ok and common to make those mistakes. You need to give yourself more opportunities to use those terms to get better at using them. Doing more questions certainly help, but you need to space them out so that you can have constant revision. Watching YouTube videos on physics will help as well.
If you think you need some one-on-one help, please don’t hesitate to drop me email at changphysicsclass@gmail.com.
If there are more topics you want me to cover, drop me a comment below.
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