Hands-on Activity Friction Force

Learning Objectives

After this activity, students should be able to:

• Describe how friction varies based on the surfaces of two objects in contact, and provide examples.
• Explain how friction affects objects in motion.
• Control a robot with a touch sensor.
• Measure and record data from an experiment.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

To share with the entire class:

• LEGO MINDSTORMS EV3 robot, such as EV3 Core Set (5003400) at https://education.lego.com/en-us/products/lego-mindstorms-education-ev3-core-set/5003400#lego-mindstorms-education-ev3
• LEGO MINDSTORMS Education EV3 Software 1.2.1, free online, you have to register a LEGO account first; at https://www.lego.com/en-us/mindstorms/downloads/download-software
• computer, loaded with EV3 1.2.1 software
• 2 surfaces, each a distance of 10 feet: 1) a rough surface such as carpet or gym mats, 2) a smooth surface such as tile floor, linoleum or glass
• stopwatch
• various materials to serve as alternatives to rubber robot tires, such as tape, string, rubber bands
• Steps to Construct the Trailer
• Friction Force Pre-Assessment, one per person
• Friction Force Data Sheet, one per person
• Friction Force Post-Assessment one per student

Note: This activity can also be conducted with the older (and no longer sold) LEGO MINDSTORMS NXT set instead of EV3; see below for those supplies:

• LEGO MINDSTORMS NXT robot, such as the NXT Base Set
• LEGO MINDSTORMS Education NXT Software 2.1

Worksheets and Attachments

Pre-Req Knowledge

Familiarity with the concept of force.

Introduction/Motivation

Can you imagine a world without friction? This world would be a rather bizarre world to live in. What would be different? Without friction, you would not be able to walk or run, and wheels of cars, buses, and trains would not be able to turn. This is quite difficult to imagine! It is because of friction that we can do all the activities we enjoy in our daily lives.

Let's go through what happens every time we take a step. We plant a foot on the ground and at the instant we push down and our feet or shoes come in contact with the surface of the ground, friction acts in the opposite way. This means we can "push" our feet against the ground and walk—instead of slipping.

Imagine trying to play basketball, soccer, bowling or even baseball on an ice skating rink—a surface with very little friction. What would happen? (Listen to student ideas.) You might fall down, slide around and not be able to get back up! Since we are so accustomed to experiencing friction all the time, we can only come to appreciate this force when we close our eyes to imagine how bizarre our world would be without this force!

In today's experiment, you have been hired to work as engineers for the car company Super Cars. This company is a multimillion dollar corporation that is investing their resources on testing different types of wheels on different surfaces to see how friction and traction affects a car's motion. As engineers, you will test out wheels with and without rubber tires to see which provide the best traction on rough and smooth surfaces. As engineers we will draw conclusions from our tests and then use this new knowledge to select the material that best enables our cars to travel a certain distance in the least amount of time.

Procedure

Background

In this activity, the LEGO robot pulls a trailer attachment across different surfaces for a distance of 10 feet. The LEGO brick must have the program "friction.ev3" file downloaded. A LEGO MINDSTORMS touch sensor is used to control the robot. Once it is pressed, the robot moves forward until the sensor is pressed again. Students work and participate as an entire class rather than in smaller groups.

Before the Activity

• Make copies of the Friction Force Pre-Assessment, Friction Force Data Sheet and Friction Force Post-Assessment one each per student.
• Construct the LEGO robot using the "Five Minute Bot" instructions provided here: https://www.youtube.com/watch?v=Dhe2jXi3Fc4
• Construct the two-wheeled "trailer" attachment that the robot drags. All materials are included in the LEGO kit; see the Steps to Construct the Trailer for images to help build the trailer.
• Make sure to fully charge the EV3 brick battery packs in advance. Uncharged bricks may alter the robot speed.
• Download the LEGO software on the computer. Then download the Friction Force EV3 Program "friction.ev3" on the brick using the LEGO software. Follow these steps to download this ev3 file: First, open friction.ev3 using the software. Once the file is open, connect the robot to the computer via USB, then click the download button on the software home page.
• Make sure motors are connected to the A and B ports of the EV3 brick and the touch sensor connected to port 1 of the EV3 brick.
• Measure 10 feet each of carpet runway and smooth flooring runway for the robot to travel. Use objects found in the classroom to mark starting and finish lines.

With the Student

1. Administer the pre-activity assessment before starting the activity.
2. Present students with the Introduction/Motivation content.
3. Hand out the data sheets.

4. Begin with the set-up shown in Figure 1. For this trial, the wheels on the trailer should not have rubber tires and the surface should be a rough or textured surface, such as a carpeted floor.
5. Conduct the trial:

• Place the robot at the start position and run the "friction.ev3" program.
• Once you run the program, press the touch sensor to start the robot moving forward. As soon as the robot starts moving, use the stopwatch to start timing.
• Let the robot to travel 10 feet to the finish line. When the robot reaches the finish line, stop the timer and press the touch sensor to stop the robot.
• Have students record the time on their data sheets.

6. Repeat the trial steps (#5) on tile floor, as shown in Figure 2.

7. Cover the wheels of the trailer with the rubber tires and repeat the trial steps (#5).
8. The set-ups for the third and fourth trials are shown in Figures 3 and 4, respectively.

9. Once students have recorded measurement data from the four trials, have them individually answer the four analysis questions on the data sheet. Then discussion their results and conclusions as a class. Have students turn in their data sheets for grading.
10. Next, continuing to act as engineers, ask students to brainstorm materials that could be used on the trailer wheels as alternatives to rubber tires. Provide a few example items for students to pick from, such as tape, string and rubber bands.
11. Have each student draw a design of their alternative wheels, with all materials labeled. Time permitting, let students add their alternative wheel design to the trailer wheels and test their designs by conducting additional trials.
12. Administer the post-activity assessment.

Vocabulary/Definitions

force: A push or pull that can cause an object's motion to change.

friction: A force that resists relative motion between two objects in contact.

motion: A description of an objective relative to its location. Motion describes how fast an object changes its location.

traction: The friction force allowing an object to stick to a surface that it is in contact with.

Assessment

Pre-Activity Assessment: Administer the four-question Friction Force Pre-Assessment to gauge students' prior knowledge of the concept of friction and how it affects the motion of objects.

Data Sheets: During the activity, have students complete the Friction Force Data Sheet to record their data and answer questions on the results of the experiments, based on the friction present in each trial. Give students times to work individually on the data sheet, and then gather students together as a class to discuss the results and conclusions. Collect the data sheets to assess each student's comprehension of the concepts.

Post-Activity Assessment: At activity end, administer the six-question Friction Force Post-Assessment to evaluate students' understanding of the concept of friction, how it affects the motion of objects, and how it affected the activity experiments. Compare students' pre- and post-activity assessments to gauge how much they learned during the activity.

References

Copyright

Contributors

Supporting Program

Acknowledgements

This activity was supported by the Central Brooklyn Robotics Initiative (CBRI) and the Applying Mechatronics to Promote Science (AMPS) Program funded by National Science Foundation GK-12 grant no. 0741714. However, these contents do not necessarily represent the policies of the NSF and you should not assume endorsement by the federal government.