DASI-P - Skateboard Push Selected Response

What important physics idea is this question targeting?

The question is testing if students can construct an argument using Newton's Laws to explain that more force will result in more acceleration. (I)
This task targets Newton’s Third Law — it’s designed to probe whether students understand that the forces Carlos and Devin exert on each other are equal and opposite, even though Carlos is stronger. (C)
This task targets whether or not students can apply Newton's Laws correctly to real-world situations with different variables. (V)

Which answer best describes what student A's response indicates about their physics understanding?

This student correctly recalls and uses a = F/m. However, they think that Carlos’s greater strength determines the net force on Carlos. Instead Carlos is Devin, so Devin should experience the greater force. (I)
They correctly recall and use a = F/m, showing comfort with Newton’s Second Law, but apply it to the wrong scenario — treating the push as one-sided rather than mutual. They don’t recognize that in this interaction, both forces are part of the same force pair. (C)
This student is beginning to reason through how differences in force and mass affect motion outcomes and can write their ideas clearly. (V)

Which of the following options would best support Student B in being able to correctly respond to this question?

I would have us create two side-by-side force diagrams: one for Carlos and one for Devin, labeling equal and opposite forces from the push. We would then talk about how to identify Newton's Third Law force pairs.(C)
I’d organize a lab where students push a rolling cart or a chair and gradually add more and more weight to the chair to see how far it rolls each time. We would then discuss how the cart felt the same force each time, but it accelerates less as more and more weight is added. (I)
I’d ask them to draw a timeline of what they think is happening during and after the push, using arrows to represent changes. (V)

Student B's response:
“They all experience the same gravitational force. My reasoning for this statement is because all objects feel the same gravitational force which is 9.8 m/s. The distance and possibly the air resistance are the only things that could change the outcome but I don’t think they matter here.”

Which answer best describes what student B's response indicates about their physics understanding?

The student has identified all of the relevant information, but has not fully explained how to use Newton's Laws. (V)
The student is not applying Newton’s Third Law — they believe Carlos exerts more force on Devin than Devin exerts on Carlos, even though they’re in a mutual interaction. This is clearest when they say Devin “receives more force.” (C)
The student has a strong grasp of physics understanding for what happens to Devin but not Carlos. They need help to consider both of the people in the interaction and link that explanation to their freebody diagrams. (I)

Which of the following options would best support Student B in being able to correctly respond to this question?

I’d hand pairs of students two force sensors together and ask them to press the sensors together so that one is experiencing a bigger force than the other. They should observe that both sensors read the same and we would discuss why, and how this is consistent with Newton's Second Law.(C)
I would have the student sit in a rolling chair and push himself against the wall. We would discuss whether or not someone can actually push themself and how the motion varies based on the strength of the push. We would then revisit the Carlos and Devin question to see that both students should move. (I)
I’d have students graph how they think Carlos and Devin’s speeds change during and after the push, and compare that to the diagrams that they drew for this question. (V)