Students will be able to define friction and describe the major factors that influence the magnitude of the force of friction acting on an object sliding on a surface.

Students investigate factors that affect friction on sliding wooden blocks.

15 minutes

The goal of this lesson is for students to investigate the factors that affect friction. Students do this in an inquiry lab where they come up with the variables and test how those variables affect the force of friction. In this lab, students are asking questions about what affects friction (SP1), collecting and analyzing data (SP4), and finally constructing explanations (SP6) by making claims about the relationships of each variable to friction.

To begin class, I have students work in pairs for this activity. To have students grouped randomly, I have them use their cell phone partners to find a partner to work with for the lab, shown in Classroom Strategy: Cell Phone Speed Dial Partners.

After they find their partner I pass out the Friction Lab packet and explain what were are going to do for the day. Before I tell them anything about the lab, I ask them to have one partner read the lab to the other partner so they know what they are going to investigate. I have them pre-read the lab so that they can get a sense of what they will be doing during the lab, as shown in Classroom Strategy: Pre-Reading.

When students have finished reading, I ask them to explain to me what they are doing and they say that they will investigate the factors that affect friction. So I tell students before they collect quantitative force data, I want them to spend time trying to come up with what factors could affect friction by exploring using the materials for the lab. I give students about 10 minutes to come up with a list of things they think affect the friction between the blocks and the surface. This section really focuses on students making observations and coming up with variables they think affect friction, as shown in Classroom Strategy: Lab Exploration.

15 minutes

After students have had time to come up with a list of factors they think affect the friction, we have a class discussion and compile a class list of factors. I ask students to volunteer the factors that they found in their explorations, making sure they support why they think that factor affects friction. After each contribution, I ask the class if any other groups came up with the same factor, as shown in Classroom Strategy: Modeling. Once we have all of the factors students think are important to investigate, I have students investigate 4 of the options listed on the board. Students usually come up with the following variables: mass or number of blocks, surface area of blocks (linking/stacking blocks), speed of pull and type of surface.

35 minutes

After the class discussion, I provide students with Newton spring scales which they will be using to collect the force data. I show them a demonstration of how to use the spring scale and what data they should record so that students can get straight to work with no questions asked. When I demonstrate the spring scale, I make sure to tell students to use the side with Newtons and I show them how to hook one end to the blocks and to pull with a constant force. After the demonstration, I ask the students if they have any questions before starting the data collection portion of the lab.

Students work conducting 4 experiments where they investigate the effect of 4 different variables on friction. Two pairs (4 students) work together to share materials and collect data but each pair writes on their own copy of the lab. The students select the factor they want to test first and then they determine how to change the factor while keeping the other factors constant. For examples, when students change the type of surface, they keep the number of blocks, surface area and speed of the pull constant and change the surface to carpet, wax paper, cork, etc. They continue collecting data for each factor until the data is collected. As students are working, I walk around to make sure students are keeping the variables other than the factor they are testing constant as well as making sure that they are measuring in Newtons.

When they have collected all of their data, I ask them to complete the data analysis question for each experiment they conducted. In this section, they analyze the effects of each factor on the friction between the block and the surface. This goes pretty quickly and they are able to complete all four experiments as well as analysis before the end of class.

5 minutes

To end class, I have students take a post-it note from the resource bin at the center of the table and gets to chose from the red, yellow or green light. They must complete the sentence starter on the light they choose, as shown in Classroom Strategy: Stoplight Exit Slips.

The Red Light: Today my learning stopped because...

The Yellow Light: Today I considered a question, new idea or perspective...

The Green Light: Today I learned __________ because...

When they complete their sentence, they stick the post-it note on whatever light they choose. The stoplight is at the front of the room whenever they finish writing their response to a light.

I do this to get an idea of where students are at in learning the material in a way that they can anonymously express exactly what they are learning or exactly what they are struggling with.