Student Conception: Acceleration is "speeding up"

[Matt Anthes-Washburn]

Student Conception: Acceleration is “speeding up.”

Students may only be familiar with acceleration in the sense of speeding up. They may think of slowing down as “deceleration,” as it is used in common language, when in fact it is just negative acceleration, or acceleration in the opposite direction. Students also may not recognize a change of direction as a case of acceleration.

Identifiers   
Listen for the word “deceleration.”

Formative Assessment Question
Ask students to observe your motion. Walk in specific directions at constant speed, change speed, and change direction.  Ask students to raise their hands any time they recognize acceleration. 
Ask students to identify and describe different cases of acceleration, and listen for whether they include negative acceleration and changes of direction.

Interventions
In PTG #3, students analyze many different cases, and identify the acceleration.
In PTG #6, a car comes to a stop. Teachers should draw students’ attention to the negative acceleration.
In PTG #7, students identify different cases of acceleration in an amusement park ride. Push them to identify not only cases of increasing speed, but also decreasing speed and changing direction. These are the parts of the ride that you “feel” in your body.

[Tracy Greeley-Adams]

I felt the PTG for activity 3 does a nice job of reinforcing negative acceleration in terms of F=MA and examples like the ice skater stopping and the running back getting tackled.  In terms of the math my students were able to understand and see negative acceleration outside of the dot timer graphs.