Investigating the effects of balanced and unbalanced forces on the movement of an object.
• Read about general preparation in the “Classroom Management” chapter.
• Read about the project so you have a good idea of what to do.
• Define how you want to introduce this project: Use the video provided for the project in the WeDo 2.0 Software, or use material of your own choice.
• Determine the end result of this project: the parameters to present and produce the document.
• Make sure that timing allows for expectations to be met.
2. Explore phase
The introductory video may set the stage for the following ideas to be reviewed and discussed with students.
It has been a long time since humans first attempted to move large objects around. From ancient civilisations to the modern age, various tools have been used to push or pull objects.
- When you do not succeed in pulling something, it is because it is being pulled in the opposite direction with the same or a greater amount of force.
- When an object starts to move, the force is greater in the direction of the movement.
- On earth, friction has a role to play.
- It is easier to pull a weight along a smooth surface than it is along a rough surface, due to the reduction in friction.
The topic of force and motion was explored and explained in detail by Sir Isaac Newton in the 17th century. You experience the laws of physics, that Newton defined, on a daily basis.
Questions for discussion
- Name different ways in which an object can be moved.
To make it move, pull or push it, or, more generally, apply a force to it.
- Can you explain friction? Is it easier to pull something on a normal surface than on a slippery one?
This question refers to friction. It is easier to move an object on a slippery surface than on a rough one.
Depending on the mass of an object, it can also be more difficult to move the object on a slippery surface, because there is less grip to push or pull it.
- Predict what will happen if the pull force is greater in one direction than the other. This answer should be based on students’ predictions. This means that at this point, your students’ answers may be incorrect. After the lesson, students should be able to discuss the fact that the motion of an object depends on the direction of the greater force.
- Can you describe the relationship between balanced forces and an object’s ability to move?
Unbalanced forces can cause a change in an object’s motion (speeding up, slowing down, etc.)
Ask your students to collect their answers with text or pictures in the Documentation tool.
3. Create phase
Build and program a Pull-robot
Students will follow the building instructions to create a Pull-robot. The Pull-robot will pull various objects that are placed in its basket. This investigation can be carried out on various types of surfaces, such as wood or carpet. Use the same surface for the entire project.
1. Build a Pull-robot.
The wobble module featured in this project uses a bevel gear. This bevel gear changes the axis of rotation, from vertical to horizontal, bringing the motion from the motor to the wheels. The basket has sliding bricks to reduce friction.
2. Program the robot to pull an object.
This program will display a 3, 2, 1 countdown before the motor turns on for two
seconds at motor power 10.
Before your students begin their investigations, ask them to adjust the parameters
of the program so that they fully understand it.
Test the Pull-robot
Using this model, students should be able to conduct an investigation about pull forces.
1. Investigate by adding light objects and then heavy objects to the basket until the device stops moving.
It will take around 300 grams on a regular surface to stop the Pull-robot from moving. Students can use any object, but nothing too heavy, as the goal is to reach equilibrium. At that point, students have balanced forces in front of them. You can use an arrow to symbolise the direction of the force.
You can also use the small tyres as objects to place in the basket. They will increase the friction on the basket side.
2. With the same amount of bricks in the basket, put the large tyres on the model and carry out tests.
Ask the students to put the tyres on the Pull-robot. This will cause the friction between the wheels and the surface to be greater on the Pull-robot side, increasing the force pulling in that direction. The system will suddenly become unbalanced.
This evidence supports the idea that when a pull force is greater than opposing forces, objects should move.
3. Find the heaviest object you can pull with your model when it is fitted with tyres.
This final step will depend on the friction of the surface.
Use the “Investigate more” section of the student project as an optional extension. Keep in mind that these tasks are an extension of the “Investigate” section and are
designed for older or more advanced students.
The Pull-robot that students are working with uses a bevel gear mechanism to change the direction of the motor rotation. It does not greatly increase the strength of the movement.
1. Build a different Pull-robot.
Ask the students to explore new designs for a pull machine. Ask them to build their own models, carry out the same tests as with their original Pull-robot, and compare the results of the two investigations. The students can refer to the Design Library for inspiration.
Find the most powerful machine in the classroom When the students have finished their tests, organise a tug of war contest:
- Pair up two teams.
- Attach the robots back-to-back with the LEGO® chain.
- Ask the teams to place equal amounts of weight and mass in the baskets before starting the contest.
- Tell them to start their motors at your signal, so that they pull away from each other. Which is the strongest?
4. Share phase
Complete the document
Ask the students to document their projects in different ways:
- Ask them to take screenshots of their results.
- Ask them to compare images of their models with real-life images.
- Ask them to record project presentation videos.
Students may collect data in a chart format or on a spreadsheet.
Students may also graph the results of their tests.
At the end of this project, students should present the results of their investigations.
To enhance your students’ presentation:
- Make sure students use words like balanced force, unbalanced force, push, pull, friction, and weight.
- Ask them to use arrows to represent force.
- Ask them to put their explanations into context.
- Ask them to analyse their projects in terms of real-life situations in which they have observed balanced and unbalanced forces.
- Discuss the connection between their findings and these particular situations.
Scientific understanding assessment rubrics
You can use these assessment rubrics with the observation rubrics grid, which you will find in the “Assess with WeDo 2.0” chapter.
During the Explore phase, make sure each student is actively involved in the discussion, asks and answers questions, and correctly uses the terms push and pull, forces, and friction.
- The student is unable to provide answers to questions, participate in discussions, or adequately describe the ideas of “push and pull” and relate to them as forces.
- The student is able, with prompting, to adequately provide answers to questions or participate in discussions, or with help, describe “push and pull” as an example of force.
- The student is able to provide adequate answers to questions, participate in class discussions, or describe push and pull as an example of force.
- The student is able to extend explanations in discussion or describe in detail the concept of force with push and pull.
During the Create phase, make sure that each student is working as part of a team, can make predictions about events, and can use the information gathered during the Explore phase.
- The student is unable to work as part of a team, make predictions about events, or use gathered information.
- The student is able to work as part of a team and predict, with help, what might happen during the investigation.
- The student is able, with guidance, to gather and use information, work as part of a team, contribute to team discussions, make predictions, and gather information to use in a presentation.
- The student is able to work as part of a team, serve as the leader, and use gathered information to justify predictions that explain the forces of push and pull.
During the Share phase, make sure that each student can explain what is happening with their model in terms of force, has tested different combinations and can predict others, and can use important information from the project to create a final report.
- The student is unable to engage in the discussion about the investigation, explain the model using the concept of force, or use information to create a final project.
- The student is able, with prompting, to engage in the discussion about forces, complete multiple testing scenarios in order to make predictions, and use limited information to create a final project.
- The student is able to engage in discussions about the investigation of forces and use the information gathered during testing to produce a final project.
- The student is able to engage extensively in class discussions about the topic, and use the information gathered to create a final project that includes additional elements.
Presentation and problem-solving assessment rubrics
You can use these assessment rubrics with the observation rubrics grid, which you can find in the “Assess with WeDo 2.0” chapter.
During the Explore phase, make sure that each student can effectively explain their own ideas and comprehension in relation to the questions posed.
- The student is unable to share his/her ideas in relation to the questions posed during the Explore phase.
- The student is able, with prompting, to share his/her ideas in relation to the questions posed during the Explore phase.
- The student adequately expresses his/her ideas in relation to the questions posed during the Explore phase.
- The student uses details to extend explanations of his/her ideas in relation to the questions posed during the Explore phase.
During the Create phase, make sure that each student makes appropriate choices (i.e., screenshot, image, video, text) and follows the established expectations for
documenting their findings.
- The student fails to document findings throughout the investigation.
- The student documents his/her findings, but the documentation is incomplete or does not comply with all of the established expectations.
- The student adequately documents findings for each part of the investigation and makes appropriate choices and selections.
- The student uses a variety of appropriate methods for documentation and exceeds the established expectations.
During the Share phase, make sure that each student uses the evidence that they gathered during their investigations to justify their reasoning, and that they adhere to established guidelines when presenting their findings to an audience.
- The student does not use evidence from his/her findings during the presentation or does not follow established guidelines.
- The student uses some evidence from his/her findings, but the justification is limited. In general, established guidelines are followed, but may be lacking in one or more areas.
- The student adequately provides evidence to justify his/her findings and follows established guidelines for presenting.
- The student fully discusses his/her findings and thoroughly utilises appropriate evidence to justify his/her reasoning, while following all established guidelines.
To ensure success, consider giving more guidance on building and programming, such as:
- Explain the use of motors.
- Explain simple program strings.
- Explain how to conduct an investigation.
- Define factors to focus on, such as pull and friction forces.
Be specific about how you would like them to present and document their findings. For example, a team sharing session.
For an additional challenge, allow extra time for experimentation with studentcreated design, building, and programming. This will allow them to explore the additional laws of push and pull. To extend the investigation, ask your students to compare the strength of their robots by pairing them in a tug-of-war contest. Prepare for the excitement!
Students are likely to believe that if something is not moving, there are no forces acting upon it. A good example to demonstrate this is trying to move a car when
the handbrake is on. Because the car is not moving, students tend to believe that there are no forces involved, yet there is. Scientifically, it’s understood that several
balanced forces are at work.
Explore what forces are and how they can make objects move.
Create and program a robot to investigate the effects of balanced and unbalanced forces on the motion of an object.
Document and present your findings about forces.
Download, view or share the student worksheet, either as an online HTML page or a printable PDF