Science Assessment ~ Ideas ~ A force is a push or a pull between two objects.

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

Sub-Ideas
Items & Student Performance
Misconceptions
NGSS

Students are expected to know that:

If no forces (or forces that add to zero) act on a moving object, then the object will maintain a constant speed.
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

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.
Items will not include situations in which objects are at rest.

Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID Number	Knowledge Being Assessed	Grades 6–8	Grades 9–12	Select This Item for My Item Bank
FM067003	Use of tables of speed versus time, and information about forces acting on an object, to determine the object's speed at various times.	34%	46%
FM100001	It is possible for an object to be moving at constant speed without a force pushing or pulling it.	26%	35%

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.	43%	40%
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.

NGSS Statements
Code	Statement
PS2.A MS	The motion of an object is determined by the sum of the forces acting on it; if the total force on the object is not zero, its motion will change. The greater the mass of the object, the greater the force needed to achieve the same change in motion. For any given object, a larger force causes a larger change in motion.
PS2.A HS	Newton's second law accurately predicts changes in the motion of macroscopic objects.