Hands-on Activity Putting Robots to Work with Force & Friction

Learning Objectives

After this activity, students should be able to:

• Determine the mass of sand in a bottle.
• Explain the concept of pushing.
• Describe the concept of mass and how it relates to force.
• Explain the idea that friction slows the motion of objects.
• Predict outcomes based on measurements.

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

Each group needs:

• pan scale
• plastic water bottles (recycled) filled with sand (varied amounts per group)
• Making Robots Work Worksheet, one per person
• Robot Quiz, one per person

Each class needs:

• 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
• bag of playground sand
• paper or plastic funnel (a rolled-up piece of paper can be used to make a funnel)
• roll of masking tape
• yard stick or tape measure
• black marker

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
• computer, loaded with NXT 2.1 software

Worksheets and Attachments

Pre-Req Knowledge

Measurement, knowledge of measuring tools.

Introduction/Motivation

(Have ready a few photos of snow plows to show students.)

What happens when there is a lot of snow outside? How do cars or buses move from one place to another? (If students do not mention snow plows, ask the following question.) Does snow prevent cars from moving? What machine could be used to remove snow? (Once the students have mentioned a snow plow, show them pictures of various snow plows.) A snow plow is a complex machine made up of many simple machines.

Today we will look at a robot that will apply a force to an object and move it—similar to how a snowplow moves snow. (Note: As a different option, show a video of a snow plow in action, found at https://www.youtube.com/watch?v=oUBhPeWeoqs, for example, or search for other relevant videos on the Internet.)

Before starting the activity, explain to students that engineers first develop models, or prototypes, and make predictions before building full-size machines. Engineering design involves building a prototype and testing it, recording data, and then building a better model based off of that data. The prototypes allow engineers to determine if their predictions are correct. Can you image engineers building a truck engine and having it all work perfectly the first time it's used? Engineers typically have to go through several models and revisions before the truck engine functions the way they designed it to work.

We will go through a similar process by using an EV3 robot to test how far the robot can push different amounts of sand. In order to complete this activity, you must first learn about the concepts of force, mass, and friction.

A force is any push or pull on an object. It is a very simple, yet important, concept of science and engineering. One example of force is that of pushing a grocery cart full of food and other supplies. Another example is of a dog pulling its owner by a leash around its neck. Forces are used to move things around us. They can act directly on objects or be used to move parts of objects. For example, a car or truck with a snowplow is made up of many parts that work together in order to push the car forward. Can you think of more examples of pushing and pulling? (Possible examples include: crane pulling up a steel beam, a child pushing a toy car, or a visitor pulling open the door to a building.)

Mass is the measurement of the "bulk" of an object. Sir Isaac Newton first defined mass as the "quantity of matter ... arising from its density and bulk conjointly." A more standard definition used today is that mass is an object's resistance to motion. This means that a heavier object of the same material will require more force to move it with the same acceleration. Since the Earth has gravity, a greater mass on Earth will always have more weight. Can you give an example of a light object and a heavy object? Which one is easier to pick up? Notice how an object with greater mass (and therefore greater weight) is harder to move.

Now that you know about mass, what do you know about friction? (Allow students time to answer the question; encourage brainstorming among the class.) Friction is a force that resists the motion between two surfaces. In other words, it pushes back on an object whenever it tries to slide across a surface. Since most solid surfaces are not completely smooth, the rubbing between the two surfaces causes resistance to motion. To illustrate this point, rub your hands together and "feel" the friction. Now rub your hands along your desk. Do you notice any difference between the surfaces? Now, imagine that you are a robot pushing a container across the floor. Is it an easy or a difficult task? Does it depend on how heavy the object is? (Allow students time to answer the questions; encourage brainstorming among the class.) The greater the mass, the more friction there is to oppose the object from moving forward.

In the experiments that you are about to perform, you will visually see the effects of mass and friction on different masses that are being pushed by the robot.

Procedure

Before the Activity

• Build the LEGO EV3 Five Minute Robot provided in the core kit. Instructions can be found at https://www.youtube.com/watch?v=Dhe2jXi3Fc4.
• Program the robot using the GoProgram file (or, if experienced, make your own program that has the robot go forward for four seconds at 50% power).
• Using a funnel, pour different amounts of sand in the plastic bottles, with one bottle for each group. Using amounts of ~40, 120, and 200 grams is recommended.
• Labels the bottles 1-X (X = to the total number of groups in your class), using masking tape and a black marker.
• Create a "robot testing station" using a length of masking tape laid out in a straight line to form a track. A 10 ft. space that is freely accessible is suggested, such as a hallway or dedicated space in classroom, for the track. Add a strip of tape perpendicular to your straight line, designating your track's "starting line."
• Test the robot by having it push the different sand bottles (test on the actual testing station surface). If there is not a noticeable difference in distance that the robot pushes the bottles, consider reducing the power on the robot's motors, or add more sand to each bottle.
• Make copies of the Making Robots Work Worksheet and Robot Quiz, one each per student.

With the Students

• Explain to students the concepts mentioned in the Introduction/Motivation section.
• Pass out the Making Robots Work Worksheet and ask students to write their names on them.

Part 1: Prediction and Measurement

1. Provide each student group a random bottle of sand (filled to different levels).
2. Instruct students to answer questions 1 and 2 on their worksheets, thus forming their hypotheses for the activity. (Questions: How can machines help us to move objects? What factors can make it easier or harder to push an object forward?)
3. Have the students predict the mass of their sand sample.
4. Ask them to record the mass prediction of their sample on their worksheets.
5. Next, instruct them to measure the actual mass of the sand sample using a pan scale. Have them record this mass on their worksheets.
6. Ask students to predict how far in centimeters the robot will push the bottle of sand, and record it on their worksheets.
7. Have students take their bottle of sand to the robot testing station and place it on the starting line.

   

8. Execute the program to have the robot push the sand mass for four seconds.
9. Measure the distance (in cm) traveled by the robot from the designated starting point.
10. Have the students write their robot's actual distance pushed on their worksheets.
11. Have students trade their bottle of sand with two other groups and repeat Steps 3-10. Each group should have predicted/measured three separate bottle numbers.

Part 2: Review and Share

1. Ask students the following guided question to explain the results of the activity:

• Since the robot went different distances, what changed for each round of the experiment? (Possible answers: The force of the robot on the sand container remained constant since the same program was run for all three trials; since the only thing that changed between each round of the experiment was the mass of the sand, that must be the cause of the robot travelling longer distances; the heavier amount of sand would cause more friction in the container, further slowing it down and making the distance travelled less.)

2. Instruct students to fill out the final question on their worksheet, based on their answers to the question above.
3. Review the following terms with students:

• Force – any push or pull on an object.
• Mass – the measurement of the "bulk" of an object.
• Friction – a force that resists the motion between two surfaces.

4. Instruct students to complete the Post-Activity assessment, Robot Quiz.

Assessment

Pre-Activity Assessment

Opening Questions: Gauge students' understanding of the subject by asking them the questions in the Introduction/Motivation section. Have photographs of various snow plows handy to show them and explain that snow plows are complex machines composed of many simple machines.

Activity Embedded Assessment

Activity Worksheet: Instruct students to complete the Making Robots Work Worksheet. Each student should have their own worksheet, and students should work within their group. If desired, collect worksheets at the completion of class, and evaluate students on their completion of the worksheets. Go around the room and monitor the students' progress on the worksheet sections.

Post-Activity Embedded Assessment

Robot Quiz: Have students complete the Robot Quiz. To gauge their mastery of the subject, evaluate students on their understanding of force, measurement, mass, and friction.

Mass Estimation: Give students a range of objects with different weights, and ask them to predict which object would be hardest to move, thus demonstrating their conceptual understanding.

Investigating Questions

• How will the mass affect the distance traveled? (Answer: A greater mass makes the object harder to move, and thus, it will travel less distance. Also, a heavier object will have more friction, further decreasing the distance.)
• Define force and how do we use it in daily life? (Answer: Force is any push or pull on an object. We use it to move objects around us all the time.)
• How can one measure the mass of objects on a pan scale? (Answer: The object is placed on one side of the pan scale and standardized weights are added to the other side until a balance is achieved. Then, the numerical value of the standardized weights is counted in order to get the mass of the object.)
• How can one measure the length of objects using a ruler? (Answer: An object's length is measured by lining it up with a ruler such that the zero mark on the ruler is parallel to one edge of the object. Then, the other edge should be compared with the numbers and marks on the ruler. The mark and corresponding number on the ruler that lines up with the other edge of the object gives the length.)
• Does friction slow down or increase the rate of moving objects? (Answer: Friction slows down all moving objects.)

Activity Extensions

Ask students to write short reflections on the value of force and friction and their effect on machines that move objects.

Activity Scaling

• For lower grades, emphasize the concept of pushing as a force that causes things to move.
• For upper grades, explain in detail the concept of friction and how it affects the movement of objects, as described in the following paragraphs.

Friction is a force that resists motion between two surfaces. Since most solid surfaces are not completely smooth, the rubbing between the two surfaces causes resistance to motion. Think about a sheet of sandpaper. What does its surface look like? It has little rocks and pits between them embedded in it. Now imagine the surface of sandpaper being pushed along a table. It requires more force to move the sandpaper across the surface. Since all objects have these irregularities, friction slows down the motion.

Friction is proportional to the weight of an object. Since weight is a function of mass and gravity, having a greater mass means an object will weigh more (at least while on Earth under the influence of gravity). A greater weight causes greater friction. This can be explained as the moving object "pushing down" more on the surface that it is trying to move along. The increase in the friction force is always true when the surface contact area between the objects remains the same, but it becomes more complicated to predict if the surface area is changed at the same time as the mass. In other words, if the size of the object in contact with the stationary object does not change, adding mass on top of the moving object will cause greater friction. In the case of this experiment, however, the surface area remained the same since the containers were the same size regardless of the amount of sand used.

References

Copyright

Contributors

Supporting Program

Acknowledgements

This activity was developed by 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.