Italicized font represents information to be shared orally or physically completed with the students at this time.

The non-italicized font represents additional information included to support the teacher’s understanding of the content being introduced within the CELL.

ASK WHY

Remind students that friction plays the role of both hero and villain in our world. Activities like walking and eating would be impossible without it. Nails would slip from boards, knots would come untied, and hair clips would fall out if it weren’t for friction  On the other hand, skinned knees, scuff marks on floors, and wear and tear of moving parts are caused by friction. Learn about this force then decide if you think friction is a hero or villain. 

BRANCH OUT

Remind students that mechanical engineers design and develop Olympic luge sleds to be aerodynamic. Minimal friction and top speed are of utmost importance. Even the luge racing suit is designed to minimize fluid friction!

GET FOCUSED

Inform students that the Investigation is designed to help them to answer the following Focus Question:

• How does the smoothness of the two surfaces in contact affect the frictional force between the two surfaces? The smoother the two surfaces, the less frictional force. The less smooth the two surfaces, the more frictional force.

Note: This question is located in students’  SDRs at the beginning and end of the Investigation.

Note: This is a succinct response to the Focus Question and is placed here for your reference at this time. A fully developed response to the Focus Question can be found on the PostLab page.

GO DEEPER

As a class, read the Background(s) in the Investigation. Have students read the information aloud or silently to themselves. When students have finished, discuss the following concepts as a class:

Note: These concepts are integrated into the Background(s) and are used to deepen students’ comprehension of the big ideas.

LEARN THE LabLearner LINGO

The following list includes Key Terms that are introduced in the Investigation Background(s). They should be used, as appropriate, by teachers and students during everyday classroom discourse.

• coefficient of friction
• normal reaction force
• ΣF = ma

Note: Definitions to these terms can be found on the Introduction page to the CELL.

Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.

SET FOR SUCCESS

• Review students’ findings thus far in the Core Experience Learning Lab by asking the following questions. Use the suggested responses below to guide students’ answers.

• Based on your experiments, what factors affect frictional force? Of the variables investigated, weight is the only factor that affected the frictional force.

• Based on your experiments, what factors do not affect frictional force? Of the variables investigated, velocity and surface area did not affect frictional force.    

• Tell students that during this Investigation they will be conducting trials, this time to determine whether or not the smoothness of the two surfaces in contact affects frictional force.
• Tell students that they will conduct their trials using the same method as was used thus far in the CELL.
• Ask students the following questions. Use the suggested responses below to guide students’ answers.

• During these trials, is it important that you pull the woodblock at the same velocity in each trial? No. Although students must have a constant velocity throughout a trial, the velocities between trials may differ.

• During these trials, is it important that you keep the mass of the object constant? Yes, because greater mass leads to greater weight, which leads to greater frictional force.

• During these trials, is it important that you keep surface area constant? No. The surface area does not affect the frictional force.

• Play the video below. Stop to ask students questions or answer students’ questions when necessary. Remind students to follow along with their SDRs and make any notes that they think might be helpful.
• After the video, direct students to divide into their lab groups to discuss their strategy for the lab. For example, they may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow students to anticipate the laboratory experience they will soon encounter. Students should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.

Note: Homework is posted below the video.

HOMEWORK

Tell students that they should review the Investigation in preparation for the Lab.