## Key Idea: The amount of kinetic energy (motion energy) an object has depends on the speed and the mass of the object.

*Students should know that:*

- Kinetic energy is energy of motion and applies to the motion of atoms, molecules, or macroscopic objects.
- The kinetic energy of an object is related to both the speed and the mass of the object, and the amount of kinetic energy an object has can be determined from these two factors alone.
- Any object that is moving has kinetic energy and the kinetic energy of an object that is not moving is zero.
- For objects that have the same mass, the object with the greatest speed has the greatest kinetic energy and the object with the lowest speed has the least kinetic energy.
- For objects traveling at the same speed (greater than zero), the object with the greatest mass has the greatest kinetic energy and the object with the least mass has the least kinetic energy.

*Boundaries:*

- Assessment items use the phrase “kinetic energy (motion energy)” to avoid confusing students who are not familiar with the phrase “kinetic energy.”
- Assessment items expect students to compare relative speeds and masses to determine relative amounts of kinetic energy. Students are not expected to calculate the exact amount of kinetic energy.
- Assessment items use either metric or non-metric units of speed (e.g. meters per second or miles per hour) as described in CCSS for mathematics.
- Students at this level are not expected to know the difference between “weight” and “mass.” All of the contexts used in the assessment items are ones where “mass” and “weight” are proportional to each other. When two objects are compared, they are in the same gravitational system.
- This idea refers to motion with respect to the surface of the earth. An object is considered to be “not moving” if its position with respect to a point on the surface of the earth is not changing.
- Items may show objects moving in a straight line, vibrating back and forth, or rotating. In all cases, students are expected to know only that the amount of energy of motion an object has depends on its speed and mass. In items, comparisons will be made between objects moving in the same manner (i.e., both rotating) and with the same distribution of mass from the origin.

Misconception |
Student Misconception |
Grades 4–5 |
Grades |
Grades |
---|---|---|---|---|

31% | 39% |
38% | ||

23% | 23% |
21% | ||

26% | 22% |
16% | ||

9% | 21% |
17% | ||

21% | 18% |
14% | ||

The motion energy of an object depends on its size (AAAS Project 2061, n.d.). | 21% | 19% |
13% | |

21% | 15% |
14% | ||

21% | 14% |
13% | ||

14% | 15% |
12% | ||

13% | 12% |
10% | ||

The motion energy of an object depends on its shape (AAAS Project 2061, n.d.). | 10% | 13% |
9% | |

18% | 11% |
8% | ||

4% | 6% |
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.