In this lesson, students return to the activity of jumping rope and explore the forces at play through the use of the app

Using the* force lens *students will:

- Use previously recorded performances.
- Create a path.
- Add height.
- Adjust ground height.
- Add push and pull stickers.

- Total Activity Time: 45 minutes
- Introduction: 20 minutes
- Record a video: 20 minutes
- Discussion: 5 minutes

- iPad with the Playground Physics app
- Videos created by students in the app. Students should have done this as part of
*Lesson 2.2 â€“ Fun with Force*. If you skipped*Lesson 2.2 â€“ Fun with Force*, have students record a video of someone in their group jumping rope. *Force: Jumping Rope Part II*Worksheet

**Activity**

**Introduction: 20 minutes**

- Tell students that when scientists study the world, they need to have standard ways of describing things so that other scientists can understand their data and analysis. Tell students that they are going to be learning standard ways to describe forces so that as a class, they can begin talking about the patterns they see in the activity of jumping rope and know that they are all talking about the same thing.
- Ask students what forces are. Take student suggestions and, as a class, come to the consensus that a force is an interaction between objects that causes a change in the motion of an object.
- Ask students what information might be important to know when talking about the forces on an object. Take studentsâ€™ suggestions and record them on their board.
- Share with students that when talking about the forces in physics, we want to talk about all of the forces acting on an object at a single moment and about how the motion of the object is impacted by those forces.
- Ask students what happens when you shoot a regular-sized marble at another regular-sized marble of the same size? You may want to hold up example marbles to provide a visual for students to think about. Allow students to share their answers and agree that the marble being shot would cause the marble that is being shot at to move. Then ask students what would happen if you shot a larger marble at the regular-sized marble. Again, example marbles may be helpful so that students have a visual. Allow students to share their answers and agree that the larger marble would cause regular-sized marble to move further. Ask students why the larger marble causes a bigger reaction. Allow students to share their answers.
- Introduce Newtonâ€™s Third Law to students and explain that force of the regular-sized marble on the other regular-sized marble is small and so the opposite reaction is small, whereas the force of the larger marble on the regular-sized marble is much larger, so the resulting equal and opposite force is much larger. Tell students that we call these reactions force pairs and that we can draw them with two opposite arrows that show if the force is a push or a pull.
- Go through the three examples in the â€śRecognizing Forceâ€ť portion of the worksheet as a class so that students are familiar with where to find the information displayed in the app and gain experience thinking about force pairs. Ifpossible, project these worksheets at the front of the class and have students follow along on their own copies.

**Investigation: 20 minutes**

- Tell students that today they are going to analyze the video they recorded in their group of someone jumping rope.
- Provide iPads to groups of students. Students should be working in the same group and should use the same iPad so that they have access to the videos their group recorded.
- Have students pull up a video of someone jumping rope. Each group should create a path of the motion by placing dots on the foot of the person jumping. We suggest using the foot of the person jumping because it is likely to move more with the movement of jumping then other points on the body, such as the hips or head.
- Have students open the graph drawer so they can see the graphs of the motion of the person jumping. They will also be able to see the white arrow that points in the direction that the object they are tracking is moving. Turning on the slow motion feature (turtle button) may make it easier for students to see the direction change in relation to the video they are watching. Students should place push stickers on the video in the appropriate places. Although there are many force pairs that students could indicate with these stickers, it is suggested that students focus on the feet of the jumper to be consistent with the path of motion. These stickers will make it easier for students to think about the patterns they see in the forces involved in jumping rope.
- Once students have annotated their video, have them describe the forces of jumping rope by completing the â€śDescribing Our Own Forcesâ€ť section of the worksheet.

** Discussion: 5 minutes**

- Once students have completed the worksheet, ask them if there is any data that is important when thinking about the forces involved with jumping rope that was not included in the questions on the worksheet. Allow time for students to share their ideas to this question and to share anything else that surprised them about the forces or motion in

their video. - Remember to check the â€śParking Lotâ€ť of questions at the end of the class period. Remove any questions that have been answered and have students add any new questions that may have come up.

1.

Â a) Students should circle the place where Amnaâ€™s hands are pushing against the chair.

Â b) The chair and the ground; Amnaâ€™s feet and the ground; Delennâ€™s body and the chair; etc.

Â c) The other forces exist, but we know there is an unbalanced total force Delenn is moving forward.

2.

Â a) Students should circle the place where Amnaâ€™s hands are pushing against the chair.

Â b) The chair and the ground; Amnaâ€™s feet and the ground; Delennâ€™s body and the chair; etc.

Â c) The other forces exist, but we know there is an unbalanced total force Delenn is moving forward.

3.

Â a) No, Amna is no longer exerting a force on the chair.

Â b) The chair and the ground; Amnaâ€™s feet and the ground; Delennâ€™s body and the chair; etc.

Â c) Friction from the ground is acting on the chair slowing it down.