## Topic: Force and Motion

Below is a list of key ideas related to Force and Motion. For each key idea, you will find a list of sub-ideas, a list of items, results from our field testing, and a list of student misconceptions. After clicking on a tab, click on it again to close the tab.

#### A force is a push or a pull between two objects.

Students are expected to know that:

1. A force is an interaction between objects, not a property of an object or something that resides within an object.
2. Forces can be interactions between two objects in direct contact with each other or operating at a distance as in the case of gravity or a magnetic force.
3. Forces between objects in direct contact with each other can be passive, such as a book setting on a table, or active, such as the pushes and pulls of mechanical devices or caused by various human activities.
Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID
Number

Knowledge Being Assessed

6–8

9–12

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73%

79%

28%

21%

26%

21%

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

6–8

9–12

FMM114

An impelling force (impulse or impetus) can become part of an object. For example, the force involved in throwing or hitting an object becomes part of the thrown or hit object (McCloskey, 1983; Fischbein et al., 1989).

67%

75%

FMM091

Passive objects (stationary rope, tabletop) cannot exert a force (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.

#### The magnitude of two forces can be added together.

Students are expected to know that:

1. Arrows can be used to represent forces acting on an object. The length of the arrows represents the strength of the forces, and the direction of the arrows represents the direction of the forces.
2. Two forces acting on an object in the same direction at the same time are equivalent to a single force that is stronger than either of the two individual forces and is in the same direction as the two individual forces.
3. Two forces acting on an object in opposite directions at the same time are equivalent to a single force that is weaker than the stronger of the two individual forces and is in the same direction as the stronger of the two individual forces.
4. Two forces of the same strength acting on an object in opposite directions at the same time will cancel one another.

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.
2. Students are expected to combine forces qualitatively, but they are not expected to calculate net force.
Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID
Number

Knowledge Being Assessed

6–8

9–12

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45%

59%

32%

53%

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

6–8

9–12

FMM115

Students add forces without considering the direction of the forces, i.e., they add absolute values of the forces (AAAS Project 2061, n.d.).

46%

25%

FMM116

When force arrows are used to represent opposing forces, students think the greater force wins so that the total force is equal to the value of the greater force (AAAS Project 2061, n.d.).

13%

11%

FMM094

Two forces in opposite directions will cancel each other no matter what their strengths are (diSessa, 1993).

9%

10%

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.

#### 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

6–8

9–12

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46%

51%

42%

41%

37%

37%

23%

28%

22%

24%

18%

14%

17%

14%

#### 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

6–8

9–12

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56%

65%

53%

57%

52%

59%

45%

49%

42%

50%

36%

49%

38%

39%

33%

37%

28%

36%

30%

31%

22%

22%

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

6–8

9–12

FMM107

If an object is slowing down, a force that was moving it forward must be decreasing (Clement, 1982; Watts & Zylbersztajn, 1981).

24%

20%

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.).

24%

20%

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%

22%

FMM105

If an object’s speed is decreasing, a force that is retarding the object’s motion must be increasing .

20%

19%

FMM123

When the force on a moving object is constant, the object will slow down.

21%

15%

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).

18%

17%

FMM090

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

20%

11%

FMM128

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 the entire time (AAAS Project 2061, n.d.).

18%

14%

FMM126

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, slow down for a while, and then move at a lower constant speed (AAAS Project 2061, n.d.).

9%

7%

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.

#### 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.
Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID
Number

Knowledge Being Assessed

6–8

9–12

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34%

46%

26%

35%

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

6–8

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.

#### 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.-and-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.

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

6–8

9–12

Select This Item for My Item Bank

42%

52%

31%

34%

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

6–8

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.

#### 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.-and-A moving object will maintain the same speed and direction of motion unless a force acts on it.

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.
• 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.
Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID
Number

Knowledge Being Assessed

6–8

9–12

Select This Item for My Item Bank

24%

21%

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

6–8