Plan the investigation
What students will do
Use the student handout to organize predictions, measurements, and explanations.
- Draw separate diagrams. Identify the force exerted on each block and mark the contact-force interaction pair.
- Predict the response. Analyze both blocks as one system for acceleration, then analyze one block for contact force.
- Measure the interaction. Read both contact-force arrows and accelerations. Compare the measurements with your calculations.
- Redistribute the mass. Keep the push fixed and test different mass pairs. Explain how acceleration and contact force respond.
What students will learn
- Identify forces by their source and receiving object.
- Distinguish an interaction pair from one object’s net force.
- Connect system analysis with individual-object force diagrams.
Common misconception
Do the contact forces cancel on each block?
The two forces act on different blocks. They cancel as internal forces only when both blocks are treated as one system.