PhET Collision Labs: Introduction to One Dimensional Collisions

© 2015 University of Colorado.
Type Category
Instructional Materials
Lesson/Lesson Plan , Model , Interactive 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.



In this interactive simulation the learner can manipulate the masses, initial velocities, and elasticity of two colliding balls. The model displays several quantities before, during, and after the collision including velocities, momentum, center of mass, kinetic energies, and position.

Intended Audience

Educational Level
  • High School
Access Restrictions

Free access with user action - The right to view and/or download material without financial barriers but users are required to register or experience some other low-barrier to use.

Performance Expectations

HS-PS2-2 Use mathematical representations to support the claim that the total momentum of a system of objects is conserved when there is no net force on the system.

Clarification Statement: Emphasis is on the quantitative conservation of momentum in interactions and the qualitative meaning of this principle.

Assessment Boundary: Assessment is limited to systems of two macroscopic bodies moving in one dimension.

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

Comments about Including the Performance Expectation
This interactive simulation can be used to generate quantitative data throughout the collision, and the vectors are displayed in the proper orientation as well as relative lengths that indicate the relative magnitude. This visually shows the conservation of momentum in a system. The simulation can be used during class as a whole class discussion, in small groups with guided questions, or as an individual experience. Introducing the operation of the app (especially if this is the first time learners have used this website) for the class can be helpful to clarify what controls are available and how to interpret the information they observe.

Science and Engineering Practices

This resource is explicitly designed to build towards this science and engineering practice.

Comments about Including the Science and Engineering Practice
The learner will observe the change in the velocity, including its magnitude and direction, as the two objects experience a collision. Taking that visual information and interpreting it to develop a claim about what is occurring during a collision offers students practice using models to gather evidence to support claims.

Disciplinary Core Ideas

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

Comments about Including the Disciplinary Core Idea
The interactive simulation shows the mass, velocity, and momentum of each object throughout the collision. The simulation gives the learner an opportunity to observe how changes in one of these variables affects another. For example, when velocity increases, what happens to the magnitude of the momentum? Likewise, when the direction of the velocity reverses, what happens to the direction of the momentum? Learners can also look for relationships between mass and momentum within the simulation.

Crosscutting Concepts

This resource is explicitly designed to build towards this crosscutting concept.

Comments about Including the Crosscutting Concept
During the collision simulation you can see the position and velocity before and after the collision and can compare the momentum before and after the collision.This simulation allows the learner to directly observe the pre and post position, mass, velocity, and momentum both visually and quantitatively. By running the simulation multiple times and making changes in the initial conditions, the affect on the final conditions of the simulation can be observed.

Resource Quality

  • Alignment to the Dimensions of the NGSS: The learner can observe changes in position and velocity and determine if momentum is conserved.

  • Instructional Supports: pHet offers many suggestions for using the simulation.

  • Monitoring Student Progress: The website offers a variety of suggestions for assessing student understanding while the learner is exploring the simulation.

  • Quality of Technological Interactivity: The simulation is reliable and the controls are easy to understand.