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 naval architects design ships from aircraft carriers to submarines, from sailboats to luxury yachts. To be successful, they need a working knowledge of fluid dynamics and ship resistance. One type of resistance they take into account when constructing ships is frictional resistance due to the motion of the hull through the water.

GET FOCUSED

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

• What is the relationship between weight and frictional force? As the weight of a load increased, the frictional force between the load and the surface it moves on increased.

• What is the relationship between the surface area of an object in contact with another surface and the frictional force between two surfaces? As the surface area of a load increased, the frictional force between the load and the surface remained constant.

Note: These questions are located in students’  SDRs at the beginning and end of the Investigation.

Note: These are succinct responses to the Focus Questions and are placed here for your reference at this time. Fully developed responses to the Focus Questions can be found on the PostLab page.

GO DEEPER

As a class, read the Background(s) in Investigation 1. Have students read the information aloud or silently to themselves. When students have finished, discuss the following concepts as a class:

• Frictional force is the force that opposes motion between two surfaces.
• Frictional force causes negative acceleration.
• Velocity does not have an effect on frictional force.
• Acceleration measures the change of speed of an object that is moving is a specific direction.
• All objects accelerate towards the earth at 9.8 m/s².
• Acceleration due to gravity is 9.8 m/s².

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 one Key Term that is introduced in the Investigation Background(s). It should be used, as appropriate, by teachers and students during everyday classroom discourse.

• force

Note: The definitions of this term 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 from Investigation Two.

• Based on your experiments in Investigation Two, what is the relationship between frictional force and velocity? Frictional force is independent of velocity. The two are not connected.

• Tell students that during this investigation they will be conducting more trials to determine whether or not two more factors influence frictional force.
• Tell students that they will conduct their trials using the same method as was used in Investigations One and Two.

• During these trials, is it important that you pull the woodblock at the same velocity in each trial? No.

Note: Students should understand based on their conclusions after Investigation Two that frictional force does not depend on velocity. Although students must have a constant velocity throughout a trial, the velocities between trials may differ.

• 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.