Sara Leins HORIZON HIGH SCHOOL, SCOTTSDALE, AZ
High School Physics : Unit #5 - Linear Momentum : Lesson #7

# A Collision Lab

Objective: Students will be able to estimate the speed of an object by applying momentum conservation to collisions.
Standards: HS-PS2-2 SP3 SP4 SP5 SP8
Subject(s): Science
60 minutes
1 Context & Equipment Needs - 0 minutes

Throughout this unit, students have been applying momentum conservation to a variety of example problems involving collisions. So, the goal for today's lesson is to put the law of conservation of momentum into action (HS-PS2-2). Specifically, students shoot foam darts at toy cars and then measure the resulting velocity (SP3-SP5 & SP8). I start the class with a ranking task before moving into the actual lab activity. Today's lesson ends with a fish bowl activity as their ticket out the door.

This lab requires the following materials for each group: dart gun, toy car, timing device, and meter stick.

Incorporating Vernier Equipment....Or Not?
Intervention and Extension

It is easy to incorporate technology into this lab, although I chose not to do that this time even though my school has the equipment available. My students seem to be too reliant on technology and are actually more productive when they are forced to measure, time and calculate by hand. Also, the materials used in this lab have already been purchased for previous labs in the class such as the angled launch lab and collisions activity.

In the event that more reliable data was needed, photogates could be used to better measure the velocity of the toy car and foam dart. Vernier also has a completely separate momentum and collision lab that can be completed with motion detectors. This is another great lab, but it requires much more equipment.

2 Introduction with a Ranking Activity - 10 minutes

This introduction activity is meant to gauge students' thinking and help them assess their individual level of understanding. I always have any introductory activity ready to go when students walk into my classroom to help with time management, so this ranking task is projected onto a screen at the front of the room before class even starts.

The ranking task shows the velocity of two cars before and after collisions. It then asks students to rank the different situations in terms of change in momentum. I choose not to give students a copy of this task and only project it because I am informally assessing students' prior knowledge. Students know that my expectation for this type of introduction is to write down the problem, their rankings and reasoning, along with their confidence levels, in their science notebooks.

Once the students are settled, I read the instructions to the activity. My reading of the instructions is to ensure students understand that class has started! I emphasize to students that they should work individually and take about five minutes to rank the momentum changes of the cars, explain their reasoning, and then assess their level of confidence. During these five minutes of work time, I walk around the room and informally assess how students are doing with simple glances at their work. Specifically, I'm looking to see if students recognize that the instructions ask students to rank the situations from most positive to most negative.

When the five minutes are over, I am back at the front of the room and ask students to raise their hand if they had a confidence level of 8 or above. This helps me gauge the percentage of my students that feel good about the material we'll be covering today. I make a mental note of those who are confident and use this as a guide to pace today's lesson. At this point, I reveal to the students the order: A=E, D, B=F=G, C, H.

3 Collision Lab Activity - 35 minutes

After students have completed the ranking task, it's time to move into the lab activity. I know that my students will not finish the lab write-up in class today, so I allow them to choose partners they feel comfortable meeting outside of class. Groups of three seem to work best for this lab so that there can be a timer, a recorder, and a person in charge colliding the dart and toy car. After they have chosen their groups, each student needs to come to the front of the room to grab a collision lab and the necessary materials (see equipment section).

Students start by measuring the mass of the dart and toy car before observing the characteristics of an elastic collision. When the dart strikes the toy car, they measure the distance that the car moves and the time it takes the car to cover that distance. With this information, students are able to calculate the average velocity of the car over several trials. The students repeat the entire process with perfectly inelastic collisions. Finally, students calculate and analyze the momentum before and after each collision to see if momentum is conserved.

The procedure in the lab document is straight-forward, but I still make sure to circulate throughout the room and check-in with the groups. I'm offering feedback on their timing methods and ensuring they are making and recording the proper measurements with the toy cars. I also am their biggest cheerleader when it's time to fire the dart gun so it collides with toy car!

When there is approximately 10 minutes prior to the end of class (5 minutes left of the time I've allowed for this activity), I ask students to put everything back the way they found it and return to their seats. I also tell them at this point that the lab due date is one week from today.

Collision Lab Student Sample