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Free Fall

[screen shot]

If you download the NetLogo application, this model is included. You can also Try running it in NetLogo Web


The model is designed for users to observe changes in motion (displacement, velocity and acceleration) of an object in free fall. Users can also observe changes in the mechanical energy of the object as it falls. The model also allows users to explore the conservation of mechanical energy. Finally, the users can also change the mass of the object and observe the resulting changes in the motion and mechanical energy of the object.


The model is initialized with a ball on the top of the view. The mass of the ball can be varied by a user with the MASS-OF-BALL slider below the SETUP button. The user can observe the motion of this model step by step, where each step is one second long (this maps into one tick in NetLogo). The ball’s motion is shown throughout its descent back onto the Earth, represented by the green patches at the bottom of the view. The ball’s position is traced at each second by a red dot in the View. The distance covered in a step by the ball is shown below the slider for the mass of the ball. The ball's distance, velocity, acceleration, kinetic energy, and potential energy at each second are recorded on the plots surrounding the view.


  1. Set the mass of a ball using the MASS-OF-BALL slider and press the SETUP button.
  2. Press the PROCEED FOR ONE STEP button to advance the ball by one second downward.
  3. Look at the monitors to see the distance covered in one second and the current values of kinetic and potential energy.
  4. Look at the graphs to observe the changes in motion and energy of the ball over time.
  5. Continue to press the PROCEED FOR ONE STEP button until the ball hits the Earth. (The model will stop once the next second of the ball's descent is below the surface of the Earth.)

MASS-OF-BALL is a slider that ranges from 1-10. This number can be changed at any time during the free fall of the ball.


Observe the trace of the ball as it free falls, are there any patterns?

Pay attention to the slopes of the Distance, Velocity, and Acceleration graphs. How do they change over time?

Notice how the distance covered in a step is increasing exponentially. How is this related to the Distance vs Time graph?

Watch the relationship between KE and PE as you proceed through the model. Pay attention to the KE + PE monitor throughout the descent.


How do the KE and PE change when you change the mass of the ball? What about the motion of the ball?

As you press the PROCEED FOR ONE STEP button, change the mass of the ball and then continue. What has changed as a result? How do the distance, velocity, and acceleration graphs look now?


Students can explore this computational model of a ball in free fall to - make observations regarding changes in its motion and energy to learn about conservation of mechanical energy. - relate position, velocity, and acceleration. - be introduced to some basics of computational thinking. - to learn how to use multiple computational representations (graphs, numbers and visualization of the trace of the free falling object).

This model is used by the lesson entitled "Conservation of mechanical energy during free fall". This lesson goes over changes in motion (displacement, velocity, and acceleration) and the conservation of mechanical energy during the free fall of an object.


This is a very simple model that is easy to extend. Here are some ideas on things to implement in the model:

  • Can you modify the starting height for the ball and observe what changes as a result of it?

  • Try changing the gravitational constant in the CODE tab, for example change it to the gravity of Jupiter which is 24.79 m/s<sup>2</sup>. What happens as a result of the different gravitational constant?

  • What happens if the acceleration is not constant? Can you make the acceleration depend on the velocity or time?

  • This model does not consider air resistance. How might you implement this into the model and how would it affect the motion and energy of the ball?

  • Could you change the model to show an object falling through other substances such as water?


We use the stamp primitive to trace the motion of the ball in the View. At each tick, the ball stamps an image of itself on the View, which provides the user an easy to read representation of the ball over time.


Look at the Random Balls model in the Models Library.


If you mention this model or the NetLogo software in a publication, we ask that you include the citations below.

For the model itself:

Please cite the NetLogo software as:

This model was developed as part of the CT-STEM Project at Northwestern University and was made possible through generous support from the National Science Foundation (grants CNS-1138461, CNS-1441041, DRL-1020101, DRL-1640201 and DRL-1842374) and the Spencer Foundation (Award #201600069). Any opinions, findings, or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the funding organizations. For more information visit

Special thanks to the CT-STEM models team for preparing these models for inclusion in the Models Library including: Kelvin Lao, Jamie Lee, Sugat Dabholkar, Sally Wu, and Connor Bain.


Copyright 2020 Uri Wilensky.


This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License. To view a copy of this license, visit or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.

Commercial licenses are also available. To inquire about commercial licenses, please contact Uri Wilensky at

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