Virtual Lab

Forces and Motion © 2017 PhET
This simulation activity has you investigate forces, both balanced forces and unbalanced forces. You will then relate this to work done.

You and some friends are at the park. You find some rope and decide you’d like to play a game of tug-of-war. Unfortunately, there are five people, so you can’t have an equal amount of people on each side. One of your friends suggests that the two biggest people should be on one side, while the three smaller people should be on the other side. Do you think this is a fair way to split up the teams? Why or why not?



  1. Click on the play button to open the activity. This interactive can also be accessed at https://quick.adlc.ca/force Select the “Net Force” icon.
  2. Task 1: Place two people that are the same size on opposite sides of the cart and the same distance away from the cart.

    Make a prediction about the movement of the cart.

    AFTER you have observed the actual movement, click on the sum of the forces box at the top right-hand corner of the simulation. Record the number in the data chart.

    Predicted Movement
    		Actual Movement
    (none, left, right)
    		Sum of Forces
    (0, x-left, x-right)
    Same size, same placement on rope.

    C2.7 Same size, same placement on rope

    Predicted Movement
    		Actual Movement
    (none, left, right)
    		Sum of Forces
    (0, x-left, x-right)
    Same size, same placement on rope.

    C2.7 Same size, same placement on rope
    		 none 0

  1. Task 2: Place two people that are the same size different distances away from the cart.

    Make a prediction about the movement of the cart.

    AFTER you have observed the actual movement, click on the sum of the forces box at the top right-hand corner of the simulation. Record the number in the data chart.

    Predicted Movement Actual Movement
    (none, left, right)    		 Sum of Forces
    (0, x-left, x-right)
    Same size, different placement on rope.

    C2.8 same size, different placement on rope

    Predicted Movement Actual Movement
    (none, left, right)    		 Sum of Forces
    (0, x-left, x-right)
    Same size, different placement on rope.

    C2.8 same size, different placement on rope
    		 none 0

  1. Task 3: Place two people that are different sizes the same distance away from the cart.

    Make a prediction about the movement of the cart.

    AFTER you have observed the actual movement, click on the sum of the forces box at the top right hand corner of the simulation. Record the number in the data chart.


    Predicted Movement Actual Movement
    (none, left, right)    		 Sum of Forces
    (0, x-left, x-right)
    Different size, same placement on rope.

    C2.8a different size, same placement on rope

    Predicted Movement Actual Movement
    (none, left, right)    		 Sum of Forces
    (0, x-left, x-right)
    Different size, same placement on rope.

    C2.8a different size, same placement on rope
    		 left x-left

  1. Task 4: Place two people that are the different sizes different distances away from the cart.

    Make a prediction about the movement of the cart.

    AFTER you have observed the actual movement, click on the sum of the forces box at the top right-hand corner of the simulation. Record the number in the data chart.


    Predicted Movement Actual Movement
    (none, left, right)    		 Sum of Forces
    (0, x-left, x-right)
    Different size, different placement on rope.

    C2.9 different size, different placement on rope

    Predicted Movement Actual Movement
    (none, left, right)    		 Sum of Forces
    (0, x-left, x-right)
    Different size, different placement on rope.

    C2.9 different size, different placement on rope
    		 left x-left
  2. Please return to the top of this page and click on analysis to complete the analysis questions.
  1. Which of the tasks represented balanced forces? Which of the tasks represented unbalanced forces?

    The balanced forces were seen in tasks 1 and 2; the unbalanced forces were seen in tasks 3 and 4.

  2. Do balanced or unbalanced forces cause a change in motion? Explain.

    Unbalanced forces cause a change in motion; when there are unbalanced forces, an object’s motion can be changed.

  3. Now that you have had a chance to experiment with the simulation, go back to the question at the beginning of the investigation. What do you think would be the best way to divide up your friends for the game of tug-of-war? Explain your reasoning.

    Use this answer for question 8 in Assignment C1.

  4. In which of the tasks was work done by the people on the cart? Explain.

    Use this answer for question 9 in Assignment C1.