SWBAT describe how mass and acceleration affect forces on colliding objects.

Collisions of "bumper boats" are a fun way to explore Newton's 2nd and 3rd Laws.

10 minutes

Collisions are a favorite middle school topic - all you have to do is try to navigate the hallways! Physics collisions can be difficult to measure in the lab and the math involved with calculating acceleration and force are stumbling blocks for many young physicists. This lesson can be used to explore any of Newton's Laws of Motion which relate to **PS2.A: Forces and Motion**; I concentrated on helping students recognize how mass affects the acceleration of two objects when the force is held constant (while trying to simplify the math).

While students explore Forces and Motion Core Disciplinary Ideas, they are conducting an investigation to produce data to serve as the basis for evidence that meet the goals of the investigation (**SP3**). One of the goals of the investigation is to apply mathematical concepts and processes (like basic operations and simple algebra built into Newton's 2nd Law) to this scientific question (**SP5**).

While students collide bumper boats (made from table shuffleboard pucks), **cause and effect** relationships can be used to predict phenomena in the designed system (**CCC**) which can be represented by proportional relationships (force as product of mass and acceleration) to provide information about the magnitude of the collision processes (**CCC Scale, Proportion, and Quantity**). This scientific relationship can be represented through the use of algebraic expressions and equations: force = mass x acceleration (**CCC Scale, Proportion, and Quantity**).

In order to ENGAGE students in this lesson, students respond to this prompt:

**Think of a situation where you or someone else ran into something.**

**Teacher Note: **If students have trouble generating collision situations, thinking can be kick-started by watching an appropriate "Epic Fail" video. Be sure to preview any epic fail video you want to show.

Students share a few stories and I share a story about hitting a tree while sledding. Together, we discuss:

**1. Why does it hurt more to run into ______________ than _______________?**

**2. How does how fast you are going affect the force on your body?**

**3. Does the mass of the object you hit change the force with which you hit it?**

These prompts provide a segue between students' stories of collisions and starting to explore the physics of interacting objects. To introduce the investigation, students view this video about bumper boats. Some students may not have experienced bumper boats, so the video helps stoke the enthusiasm around the investigation.

50 minutes

The EXPLORE stage of the lesson is to get students involved in the topic so that they start to build their own understanding. To help students explore in groups, students plan their investigation using the Bumper Boats Experimental Design Plan in order to answer the question:

**How does mass affect the acceleration of an object?**

This is a structured inquiry lab in which students complete some sections of the plan while other sections are provided. The design plan can be modified to include more or less structure depending on the level of your students. At this point in the year, my students have designed several experiments, so minimal instruction or guidance during the process other than to coach them to use precise scientific vocabulary in sections like "Background Research" and complete reasoning in sections like "Hypothesis" as shown in the Bumper Boat Investigation Student Work. For more on designing "Background Research" questions within structured inquiry, see this section's reflection: Designing Background Research Opportunities in Structured Inquiry.

I review student work prior to progressing on to testing the bumper boats. Once students have completed the experimental design plan, they are ready to conduct the investigation and collect data using the Bumper Boats Experimental Procedure.

**Teacher Note: **As always, safety should be stressed during this investigation. The bumper boats can become projectiles easily. While sliding the boats into each other, it is very enticing to hit them with as much force as possible. For this reason, the procedure specifies a limited distance for students to slide the boats. This is an attempt to hold the force constant as a controlled variable while students alter the mass (independent variable) to see how acceleration (dependent variable) responds. To minimize the mathematical difficulty, we discuss how the measuring the distance approximates acceleration.

20 minutes

The EXPLAIN stage provides students with an opportunity to communicate what they have learned so far and figure out what it means. This stage of the lesson presents a great place for a quick formative assessment. Here are three opportunities for explanation:

1) The first strategy for helping students explain what they have learned is to individually complete the Newton's Laws Notes Student Handout for Newton's 2nd and 3rd Laws. By completing these notes, students are able summarize the basic concepts related to inertia. Upon completion, students review their notes with a copy of the completed Newton's Laws Notes Student Handout.

2) A second "explain" strategy is to conduct short interviews with each student as they complete their notes. While having these discussions during the investigation is important to probe for student understanding, probing questions are even more important during this individual accountability part of the lab. Up until now, students have their groups to rely on when explaining their understanding. With group work, it is important to balance "group think" with individual accountability. Some prompts that help students explain their understanding are:

**1. How did the mass of the bumper boat affect its acceleration?**

**2. When the force on the boats is kept the same, what happens as mass increases?**

**3. What happens if you put more force on the bumper boats?**

**4. When the boats collide, what forces are acting on the boats?**

**5. Is the only force in this system the force on the target puck?**

**6. Does the target puck exert a force?**

**7. Where do you see balanced or unbalanced forces in this system?**

3) A third "explain" strategy is to have students answer the question:

** Did your results agree with your hypothesis? Why or why not?**

Students may write or answer the question verbally. This question is powerful because it requires students to analyze their data, make claims, and provide evidence a reasoning.

The EXTEND stage allows students to apply new knowledge to a novel situation. The novel situation in this case is to complete:

**Procedure Part 2:** If you have time, modify your investigation to answer this question:** **

**How does friction affect the acceleration of a bumper boat?**

For this extension, students write a new hypothesis, create a materials list of supplies and craft a procedure to help them explore the new question. Students conduct their investigation and complete Data Table 2. Students provide an argument answering the friction question with claim-evidence and reasoning as a final product. For more on writing arguments, visit: Writing Arguments from Evidence.

**Teacher Note: **The original inspiration for this extension was to give students an opportunity to get their bumper boats wet. I figured some students would want to try water as a way to test friction. By providing students with a sneak peak at different materials they might use (plastic wrap, wax paper, carpet, felt, plexiglass or artificial turf) helps them reign in some of the ideas that may be difficult to enact in class (ice is a common idea).

10 minutes

The EVALUATION stage is for both students and teachers to determine how much learning and understanding has taken place. There are many ways to assess learning depending on your learning objectives. Traditional assessment methods include having students write a RECALL Lab Conclusion (Part 1 and Part 2) or taking an online quiz like this one: Newton's 2nd and 3rd Laws of Motion Quiz.

Providing student choice in terms of a final project, students could choose from the "Evaluate", "Analyze" or "Apply" domains of Bloom's Revised Taxonomy.

If extension or remediation of learning is needed, we may also use Newton's Laws of Motion Interactive Presentation as a supplementary tool to explore the laws. This presentation includes links to simulations, examples and questions that can be used for assessment.