Figuring out Friction

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Students will be able to define and explore friction.

Big Idea

Students figure out the quantitative definition of friction and then see it in action!

Context & Equipment Needs

During a previous lesson in this unit students identified how Newton's Second Law can be applied in 2-dimensions, so our goal today is to introduce friction with a video and lab activity (SP3,5 & 8). Specifically, students will define friction quantitatively and qualitatively before visualizing friction in action (HS-PS2-1). Class ends with an analogy prompt closure.

This lab uses the following equipment: a wooden friction block with a rubber surface, a wooden friction block with a carpeted surface, a bare wooden friction block, a spring scale, and a random text books (procured from the students' backpacks). Prior to students arriving, I have a complete set of these materials at each lab station around the room.

Introducing Friction with a Video

15 minutes

Because there are so many resources out there I've decided to use this video to introduce friction. Before I start the video I make sure my expectations are clear: students need to be sitting quietly, listening and watching the video, and taking notes (in their science notebooks) on meaningful material. To me, meaningful material includes any reference to previously learned concepts, equations, vocabulary, and examples. I am telling my students these expectations as I'm on my way to start the video.

As we watch the video I pause it in several places to give my students an opportunity to process and internalize this new information. I use a video discussion guide to remind myself where to stop and what important material or questions I want to share with students. When I pause the video I'm somewhat flexible in our discussions, meaning if a student has questions or needs further explanation I take the time to do that. I always write down the 2 friction equations on the front board so that students copy them properly. 

Friction Activity

30 minutes

Because I know that my students will not finish the lab in class today, I allow them to choose a partner so that they feel comfortable meeting with the person outside of class.  Also, my students are mature and have a good rapport with each other, so I never have to worry about someone being left out of a pairing. In the event that someone is absent, I do make an exception for one group of three. After they have chosen their partners, they need to come to the front of the room to grab an activity document and then go to an already organized lab station.  

I announce to students that they should get right into the activity. They are already familiar with the expectation that they need to check their lab stations with the materials list to have everything needed for the lab. It is my rule that if something is missing at the end of the class that group is charged with the cost of the missing item. I find doing this holds kids accountable and ensures my materials don't fall into someone's pocket.   

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. The purpose of the activity is for students to explore how different factors affect friction, so the lab starts with students recording the maximum force applied to a carpeted block before it starts to move. They use a spring scale to record that applied force and also to record the force necessary to keep the block moving at a constant rate. After 3 trials, the students repeat the process with a bare wood block and then a rubber block. Finally, students add more weight to the blocks and repeat each of their trials.

If time allows and the students are finished collecting data, they can start working on their conclusions. The conclusion must address changes in the frictional forces throughout the lab, the relationship between an applied force and friction, and calculated values for the coefficient of friction. When there are approximately 10 minutes remaining in 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 when the lab will be due (I usually give them several days) and remind them that data, calculations, and their conclusions must be completed on a separate sheet of paper.

Analogy Closure

5 minutes

With about five minutes left of class, I ask the students to stop working and focus on me for a moment. I remind students that the purposes of today's activities were to define and explore friction. As I'm talking, I give each student a small, blank notecard.

Once everyone has a notecard, I ask students to respond to an analogy prompt that is on the front board. I've put the prompt on the board while the students were working, and it's been hidden from their view so they aren't able to think too deeply about their responses. As I reveal the prompt to the students, they must write the prompt and their responses on the index card. For this particular activity, the prompt will say "This friction activity was like _________ because _______."  

This is their "ticket out the door," meaning that they can't leave until they've handed me their card. To avoid anyone sneaking out of the room, I stand at the door and collect the cards as students depart. Once I've collected all of the cards, I read and use them to adjust my teaching practices. For example, if a student says "This friction activity was like a marathon because it was way too long." I might take a question off the activity before doing it again the following year. It's always fun to read some of their creative responses!