Teacher Demonstration
Use the live model as a shared screen demonstration before students try their own predictions and observations.
Workshop Resource
Atwoodmachine 3 Mass
Analyse Atwoodmachine 3 Mass as a Tracker video-analysis activity for kinematics, using calibrated video points and graphs to describe motion.
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.
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2. Big Ideas
Key idea An Atwood machine links the motion of two masses through a common string tension. The imbalance in weight provides the net driving force for the whole connected system.
What Students Can Learn
- Compare the two weights to predict direction of acceleration.
- Treat the connected masses as one system when finding the net driving force.
- Recognise that tension is internal to the two-mass system but acts on each mass separately.
- Relate a larger mass difference to a larger acceleration.
Guiding Question
How does changing the mass difference alter the direction and size of the acceleration?
3. Try the Investigation
Balance the Masses
Start with equal masses and observe the zero or near-zero acceleration case.
Create an Imbalance
Increase one mass while keeping the other fixed, then predict the direction of motion.
Compare Acceleration
Repeat with a larger mass difference and compare the displayed acceleration or motion.
Use a System Argument
Explain the result using net external force divided by total mass.
4. Teacher Notes
Lesson Use
Use the model to move students from single-object F = ma to a connected-system view.
Discussion Prompts
Ask: Which force drives the whole system? Why does increasing mass difference matter?
Teaching Moves
Draw force diagrams for each mass, then a simplified whole-system diagram where internal tension cancels.
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.
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Answer each question once to build your streak.
1. In an ideal Atwood machine, what provides the net driving force for the two-mass system?
2. If the two masses are equal, what should the acceleration be in the ideal model?
3. Why does a larger mass difference usually increase acceleration?
4. When analysing one hanging mass, which force acts upward?
5. What is the strongest explanation after using the model?
Expert Challenge
Unlocks after 3 correct concept-check answers on this page.
1. A position-time graph is a straight line with positive slope. What is the best interpretation?
2. A velocity-time graph crosses from positive to negative velocity. What does the crossing mean?
3. What does the area under a velocity-time graph represent?
4. A velocity-time graph has a negative slope while velocity is still positive. What is happening?
5. What is the best way to avoid memorising graph shapes without understanding?
7. Learning Pulse
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