## The Net Force and Rube Goldberg

### Julie Brown

#### Description

Roll, drop, slide, twist, and turn your middle school students' attention by exploring net force while creatively building Rube Goldberg contraptions.

#### Objectives

The student explains and shows the ways in which a net force (that is, the sum of all acting forces) can act on an object (e.g., speeding up an object traveling in the same direction as the net force, slowing down an object traveling in the direction opposite of the net force).

#### Materials

-One bag of materials for each pair of students.
-Materials bag may include but is not limited to:
-1 Grooved ruler or meter stick
-6 Straws
-1 Balloon
-2 Paper cups
-4 Marbles
-1 Aluminum foil 10”x10” square
-6 Dominoes
-4 Pipecleaners
-1 Aluminum pans (various sizes)
-1 Index cards
-1 small ball playdoe
-5 feet string

#### Preparations

1. Review the Official Rube Goldberg Web Site. This site gives background information about Rube Goldberg.
2. Review lesson procedures and make adjustments to group size, materials list, or allocated times as needed.
3. Gather materials listed in the materials list as used in the procedure. These could be presorted into boxes or bags to minimize distribution time.
4. Build a sample Rube Goldberg.
5. Make copies of rubric for the teacher’s use.

#### Procedures

1. One set of the following materials should be on the table for each student as they arrive:
1 grooved ruler,
1 marble,
1 paper or plastic cup.

2. Ask students to put the marble in the cup without placing it there by hand.

3. Give students 3 minutes then encourage them to share their ideas.

4. Discuss various ways this could be done. Introduce students to Rube Goldberg and explain his contraptions.

5. Ask students what caused the marble to continue to move.

6. Guide discussion to forces.
7. Have students develop a definition for net force.

8. Demonstrate a Rube Goldberg machine that you have built.

9. Discuss the various forces involved.

10. Instruct students that they will build one with at least 6 steps/moves. They are to list steps on an index card and will explain to the class as they demonstrate their Rube Goldberg machines and the forces they use. They are not required to use all the materials. Students should be given no more than 15 minutes to build.

11. Pair students and distribute one bag of materials for each pair of students.

12. Distribute copy of rubric. Students are to complete with name and return to teacher at the beginning of their presentation.

13. Allow students 15 minutes to build.

14. Have students stop building and give them 1 to 2 minutes to finish their index card write-ups and briefly prepare for their presentations. Presentations should be no longer than 2 minutes per group and should be done from their tables to prevent from having to move the Rube Goldberg machines.

15. Before students present, remind the class of classroom procedures while others are presenting. (Presenters get undivided attention from all. Only positive feedback allowed.) Keep presenters to their maximum time limit of 2 minutes.

16. Spend 2 to 3 minutes reviewing definition of net force.

17. The last 5 minutes should be spent on clean-up then set-up for the next class.

#### Assessments

Students will build a Rube Goldberg machine using a minimum of 6 steps, given specific materials to show ways in which a net force can act on an object; they will list the steps on an index card and explain to the class as they demonstrate their machines. This will be scored by a rubric covering the scientific principle of net force and the number of steps.

#### Extensions

ESOL/ESE modifications: Break into two class periods. Break down steps into brainstorming; sketching draft before building; allow more time for building; allow more time for presentation preparation.

Extensions of scientific principals: Newton’s Laws, gravity, acceleration, speed.