6 USA students per year group (ages 11-16), selected by teachers as average, were interviewed about instances to identify misconceptions.

Learners’ ideas

• All the students who were interviewed stated that the runner who covered the greater distance was going faster.
• Some students believe that when one object has caught up to another they must be going at the same speed: "Well for a split second they are at the same point and to get there they both need to go the same speed".
• Some students considered that speed and velocity were synonymous.
• Velocity is different from speed but the differences are not accepted scientific ones: "Velocity can be slowing down but speed, it is normally rising, but velocity can go both ways."
• Velocity is the same as the acceleration.
• Students realised that acceleration involved the idea of a change in speed but the relationship between the two quantities was not the scientific definition (i.e. change in speed/change in time). All students assumed increasing speed always meant increasing acceleration.
• Some students indicated that if an object was going fast it also must have had acceleration.

Further suggestions

• One object passing another dominates some students' ideas of relative speeds.
• One senior physics class were asked if they considered an object falling or rolling down a slope to have increasing acceleration. Despite the fact that these students had just been taught the theoretical aspects of acceleration, 70% answered that it would.

The study

Aims

Identify concepts of speed, velocity and acceleration held by students.

How the evidence was collected

Interviews were recorded and transcribed: Students were shown drawings on cards which represented various instances and events e.g. car slowing down, speeding up, overtaking, a ball dropping from an aircraft, throwing the ball up, rolling a ball down an incline and spinning a ball around on the end of a string. The interviews were conducted in a standard questioning format, but at any point, the interviewer could choose to probe more deeply into a student's understanding by extending the discussion. In addition, to verify some aspects of the interview work, a multiple-choice survey was also administered.

Details of the sample

30 students, 6 per year group, from five different schools in the USA, consisting of three intermediate (11-13 years) and two secondary (13-16 years) were interviewed. Teachers were asked to send pupils of average ability.

For the follow-up multiple-choice surveys: 113 13-14 years, 110 Form 14-15 years, 96 Form 15-16 years, 52 16-17 years (including 56 non-physics students).