The Atwood's Machine 2D Interactive is an adjustable size file that displays nicely on just about any device - on smart phones, tablets such as the iPad, on Chromebooks, and on laptops and desktops. The compatibility with mobile phones, iPads, other tablets, and Chromebooks make it a perfect tool for use in a 1:1 classroom. Its dimensions can be adjusted to just about any dimension by dragging the lower-right corner of the iFrame.

Teaching Ideas and Suggestions:

This Interactive should be reserved for later stages of the learning cycle on Newton's second law of motion, ideally after a discussion of inclined planes and vectors. It is intended for courses in which two-mass systems are part of the curriculum. The Interactive provides an environment for investigating the motion of a two-mass system. The graphical menu in the upper right corner of the simualtion allows learners to select one of nine scenarios to study. The first two of the nine scenarios include one-body, one-dimensional motion; they are warm-ups for the next seven scenarios that become progressively more complex. A second mass and a pulley are introduced in the third sccenario. An understanding of vector resolution and inclined planes becomes important in the last four scenarios. Teachers will want to preview the simulation to make decisions on which of the scenarios would be appropriate for their students.

The motion occurs in the model window on the left side of the simulation. Controls located below the model window allow a user to play, pause, rewind (to the beginning), slow down, and reset (re-initialize) the simulation. Each scenario can be customized using the sliders in the lower right of the simulation window. A trial can be performed and then an adjustment can be made.  Variables that can be changed include:
  • Mass of the left (blue) block
  • Mass of the right (green) block
  • Rotational inertia of the pulley (Scenarios 3-9)
  • Gravitational field constant (acceleration of gravity)
  • Coefficient of friction (both static and kinetic)
  • Angle of the left ramp (that the blue mass moves along)
  • Angle of the right ramp (that the green mass moves along)
  • Initial Velocity of the masses
  • View (alter the portion of the motion that is in view; most useful if the masses leave the model window)
Users have the option to view the forces acting upon the masses as vector arrows. They also have the option to show the names of the forces. In situations involving inclined planes, there is an option to show the resolution of hte weight vector into components that are parallel and perpendicular to the plane. And finally there is an option to shown the values of all forces and the acceleration. Users can use the Reset button at any time to reset the selected scenario to its default state.


Related Resources

There are a few resources at The Physics Classroom website that serve as very complementary supports for the Atwood's Machine 2D Interactive. These include:
  • Reading:
    Lesson 2 of the Newton's Laws Chapter of the Tutorial is a necessary pre-cursor to the topic of two-nass systems. The following page will be particularly useful in the early stages of the learning cycle on two-mass problems:

    Double Trouble

  • Labwork: 
    Simulations should always support (never supplant) hands-on learning. The Laboratory section of The Physics Classroom website includes several hands-on ideas that complement this Interactive. One notable lab idea is ...

    Modified Atwood's Machine

    Visit The Laboratory.

Additional resources and ideas for incorporating the Atwood's Machine 2D Interactive into an instructional unit on Newton's Laws of motion can be found at the Teacher Toolkits section of The Physics Classroom website.  Visit Teacher Toolkits.



We owe a special thanks to Physics teacher Martin Kirby for donating the Atwood's Machine 2D Simulation to our Interactives collection. Martin has contributed many other simulations to our Interactives collection. You can view them all by visiting our page listing all Martin Kirby Simulations. Or visit Martin's website ( to learn more.