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

Key Idea: If a force acts on an object in the same direction as the direction of its motion, the object’s speed will continue to increase while the force is acting.
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If a force acts on an object in the direction opposite to the direction of the object’s motion, the object’s speed will continue to decrease while the force is acting.

Sub-Ideas
Items & Student Performance
Misconceptions
NGSS

These items have been aligned to more than one key idea. To view the sub-ideas click on a key idea below.

If a force acts on an object in the same direction as the direction of its motion, the object’s speed will continue to increase while the force is acting.
Students are expected to know that:
1. If a force is acting on an object to push or pull it forward, the object will continue to move faster and faster in the forward direction the entire time the force is acting.
2. If an object’s speed is increasing, then a force must be acting on the object the entire time its speed is increasing.
Boundaries:
1. Students are expected to analyze situations involving no more than two forces acting on an object at the same time that act along the object’s line of motion. Students are not expected to analyze situations in which the force is acting at an angle other than along the object’s line of motion, which would change the direction of the object’s motion.
2. Test items will involve situations in which forces are constant, not situations in which the forces are increasing or decreasing.
If a force acts on an object in the direction opposite to the direction of the object’s motion, the object’s speed will continue to decrease while the force is acting.
Students are expected to know that:
1. If a force, either constant or changing, acts on an object in the direction opposite to the direction of the object’s motion, the object’s speed will decrease and will continue to decrease for as long as that force is greater than any force moving the object forward.
2. If an object’s speed is decreasing, a force must be acting on the object in the direction opposite to the direction of the object’s motion, and that opposing force must be greater than any force moving the object forward.
3. If a force acts on an object in the direction opposite to the direction of the object’s motion for a long enough time, the object’s speed will decrease to zero. If the same force continues to act, the object will move in the direction opposite to its previous motion.
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 or, if the object is not moving, the forces are acting along the same line.
2. Test items will involve situations in which forces are constant, not situations in which the forces are increasing or decreasing.

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
FM102001	A ball thrown into the air goes slower and slower on the way up, stops, and then moves faster and faster as it comes down.	42%	52%
FM101001	If an object is moving forward, and a force pushing it backward is greater than a force pushing forward, the object will slow down, stop, and then begin to move faster and faster in the opposite direction.	31%	34%

Frequency of selecting a misconception
Misconception ID Number	Student Misconception	Grades 6–8	Grades 9–12
FMM125	When a force acts on a moving object to slow the object down, the object will slow down for a while and then move at a lower constant speed (AAAS Project 2061, n.d.).	20%	16%
FMM124	When a force acts on a moving object in the direction opposite the object’s direction of motion, the object will move at a constant speed for a while and then slow down (AAAS Project 2061, n.d.).	19%	15%

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.