Atwood's Machine Simulation

Tom Henderson
Type Category
Instructional Materials
Informative Text , Lesson/Lesson Plan , Simulation
This resource, vetted by NSTA curators, is provided to teachers along with suggested modifications to make it more in line with the vision of the NGSS. While not considered to be "fully aligned," the resources and expert recommendations provide teachers with concrete examples and expert guidance using the EQuIP rubric to adapted existing resources. Read more here.



This simulation includes a wheeled cart on a horizontal surface that is tied to a mass with a string that passes over a pulley. The mass hangs over the edge of the table, and when the cart is released the mass accelerates down towards the ground. The learner can vary the mass of the cart and the mass of the hanging mass. The data that the simulation provides as the cart rolls and the mass falls include a motion diagram that visually shows the rate of acceleration of the cart, a motion diagram of the falling mass, and numeric results for the tension in each rope, the time elapsed, and the displacement of the objects. There is accompanying informative text in the Related  Resources section that explains how to solve two body problems using Newton’s second law. This text provides solved examples as well as additional practice.

Intended Audience

Educator and learner
Educational Level
- none -
Access Restrictions

Free access - The right to view and/or download material without financial, registration, or excessive advertising barriers.

Performance Expectations

HS-PS2-1 Analyze data to support the claim that Newton’s second law of motion describes the mathematical relationship among the net force on a macroscopic object, its mass, and its acceleration.

Clarification Statement: Examples of data could include tables or graphs of position or velocity as a function of time for objects subject to a net unbalanced force, such as a falling object, an object rolling down a ramp, or a moving object being pulled by a constant force.

Assessment Boundary: Assessment is limited to one-dimensional motion and to macroscopic objects moving at non-relativistic speeds.

This resource is explicitly designed to build towards this performance expectation.

Comments about Including the Performance Expectation
The simulation visually shows the changes in motion through the motion dot diagrams and allows the learner to explore the impact of changing the relative mass between the cart and the hanging mass on the tension in the cable and from that information the learner can calculate the acceleration of the system.

Science and Engineering Practices

This resource appears to be designed to build towards this science and engineering practice, though the resource developer has not explicitly stated so.

Comments about Including the Science and Engineering Practice
The learner is provided data related to position, time, tension, velocity, and acceleration through the simulation. This data can be analyzed to relate how changing the relative mass of the two objects in the system impacts the acceleration and tension in the string.

Disciplinary Core Ideas

This resource is explicitly designed to build towards this disciplinary core idea.

Comments about Including the Disciplinary Core Idea
This simulation relates the acceleration of each of the two objects in the system to the tension in the string between the objects so that the learner can predict the motion of the system as the relative masses are changed. There is a laboratory exercise linked in the related resources section of the website that asks the students to derive the equation that relates acceleration and force on an object. This activity would be useful to do before the lab so that students have a good conceptual understanding of what they are trying to accomplish in the physical lab.

Crosscutting Concepts

This resource appears to be designed to build towards this crosscutting concept, though the resource developer has not explicitly stated so.

Comments about Including the Crosscutting Concept
The simulation allows the learner to directly investigate the relationship between the acceleration of the system of objects and the relative mass of the objects, but the teacher will need to guide the students through designing and completing these investigations.

Resource Quality

  • Alignment to the Dimensions of the NGSS: The simulation and accompanying informative text allow the learner to explore the relationship between the acceleration, tension, and masses of the objects within the system looking for the cause and effect of making changes to the masses. This supports all three dimensions of learning.

  • Instructional Supports: There are teacher notes discussing student misunderstandings and excellent informational text for the learner about how to approach and solve two body system problems.

  • Monitoring Student Progress: There is not any advice on how to assess the understanding of the student while interacting with this simulation. The teacher could easily write assessments guiding the learner through their exploration of the simulation with questions to get the learner to think about what they are seeing on the screen and how the data they see relate to each other.

  • Quality of Technological Interactivity: The simulation is written in HTML5 which is a robust system that works well on many platforms. You do have to watch the whole simulation each time though because there is not a button to pause the simulation.