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.

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.
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

FM064004

Use of tables of speed versus time, and information about forces acting on an object, to determine its speed at various times.

46%

51%

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%

FM036003

42%

41%

FM092002

A box that is being pushed with a constant force can move faster than the person pushing it if the force of the push is greater than the force of friction on the box.

37%

37%

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%

FM090002

A wagon that is being pulled with a constant force can move faster than the person pulling it if the force of the pull is greater than the force of friction on the wagon.

23%

28%

FM068003

Use of tables of speed versus time, and information about the speed of an object, to determine the forces acting on the object at various times.

24%

21%

FM089002

A sled that is being pulled with a constant force can move faster than the person pulling it if the force of the pull is greater than the force of friction on the sled.

22%

24%

FM011005

The speed of a sailboat will continue to increase the entire time the force of the wind pushing it forward is greater than the force of the water slowing it down.

18%

14%

FM093002

A cart that is being pushed with constant force can move faster than the person pushing it if the force of the push is greater than the force of friction on the cart.

17%

14%

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.

47%

51%

FMM102

Constant force produces constant speed. Under the influence of a constant force, objects move with constant velocity (Champagne et al., 1980).

42%

46%

FMM117

When a force acts on an object in the direction of the object's motion, the speed of the object will increase for a while and then level off at the higher speed (AAAS Project 2061, n.d.).

23%

25%

FMM101

Increasing speed requires increasing force.

24%

19%

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%

FMM118

When a force acts on an object in the direction of the object’s motion, the speed of the object will increase for a while and then slow down. (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%

FMM120

When a force acts on an object in the direction of the object’s motion, the speed of the object will stay the same for a while and then increase and stay at the new higher speed. (AAAS Project 2061, n.d.)

18%

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.