Teacher Demonstration
Use the live model as a shared screen demonstration before students try their own predictions and observations.
Physics / Newtonian Mechanics
Pushing On Two Blocks, Will It Stay Or Slip?
Explore Pushing On Two Blocks, Will It Stay Or Slip? as an interactive EJS simulation for mechanics.
.png)
1. Watch or Launch
Launch the Interactive
Open the simulation, adjust the controls, and compare what changes on screen before answering the concept-check questions.
2. Big Ideas
Key idea Friction is a contact force that can adjust up to a limiting static value before sliding begins. Once the object slips, kinetic friction acts opposite the relative motion and the resultant force determines the acceleration.
What Students Can Learn
- Distinguish static friction from kinetic friction.
- Compare applied force, limiting friction, and resultant force.
- Use force arrows or graphs to decide whether the object stays at rest or accelerates.
- Connect normal reaction and coefficient of friction to maximum frictional force.
Guiding Question
At what point does the object change from staying at rest to slipping, and what force evidence shows that transition?
3. Try the Investigation
Predict the Threshold
Before changing the applied force, predict whether the block will stay at rest or slide.
Increase Force Slowly
Raise the applied force in small steps and watch how friction responds before motion begins.
Compare Static and Kinetic Cases
Once sliding begins, compare the friction value and acceleration with the just-before-slipping case.
Explain with Resultant Force
Use the difference between applied force and friction to explain the observed motion.
4. Teacher Notes
Lesson Use
Use this as a threshold lesson: students should see static friction as adjustable, not as a fixed force.
Discussion Prompts
Ask: Why can friction increase while the block remains stationary? What changes when the block starts moving? How does resultant force explain the velocity graph?
Teaching Moves
Have students mark three moments: below limiting friction, at the threshold, and after sliding. Require a free-body diagram for each.
5. Concept Check
These questions are generated from the topic and the concept illustrated by the simulation. Use them after students have explored the model.
Concept Score
Correct first attempts build a streak and unlock higher point multipliers on this device.
0page points
0current streak
x1multiplier
0best streak
Answer each question once to build your streak.
1. What happens to static friction as a small applied force is increased but the block remains at rest?
2. When does the block begin to slip?
3. Once the block is sliding, which friction model usually applies?
4. Which quantity best explains whether the sliding block accelerates?
5. Why is a free-body diagram useful here?
Expert Challenge
Unlocks after 3 correct concept-check answers on this page.
1. A block remains at rest while the applied force is slowly increased from 1 N to 5 N. What is friction doing before the block slips?
2. A block starts sliding only after the applied force exceeds 12 N. What does 12 N most likely represent?
3. Why can a sliding block accelerate even though friction acts on it?
4. If the normal reaction is doubled while the coefficient of friction is unchanged, what happens to maximum static friction?
5. A student says a rougher surface always means a larger acceleration. What is the best feedback?
7. Learning Pulse
Anonymous activity shows this resource is being discovered, revisited, and used by learners in different places.
--currently viewing
--total page views
Where Recent Learners Are From
Country or region is inferred anonymously from server location headers when available. No names, accounts, or IP addresses are shown.
Detecting locations...
Updating anonymous page activity...