Key Idea: A moving object will maintain the same speed and direction of motion unless a force acts on it.

Students are expected to know that:

  1. If no forces (or forces that add to zero) act on a moving object, then the object will maintain a constant speed.
  2. If an object is maintaining a constant speed (or is at rest), then no forces (or forces that add to zero) are acting on it.

Boundaries

  1. Students are expected to analyze situations involving no more than two forces acting on an object at the same time, and each force must act along the object’s line of motion.
  2. Items will not include situations in which objects are at rest.
Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

FMM129

A constant force is needed to keep an object moving at constant speed.

44%

44%

FMM110

A force is required to keep an object moving. Objects slow down and stop if a force is not maintained (Sadanand & Kess, 1990; Twigger et al., 1994; Jung, 1981; Champagne et al., 1980; Watts, 1983; Osborne, 1985).

21%

18%

FMM106

Moving objects stop when they run out of force (Twigger et al., 1994). An object’s force can be used up and must be replenished to maintain activity (Watts, 1983).

11%

8%

FMM090

A moving object has a force within it that keeps it moving (McCloskey, 1983; Osborne, 1985; Viennot, 1979).

11%

8%

Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.