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 automotive engineers design cars so that the amount of friction between the moving parts of the engine is reduced. Less friction means less wear and tear on the engine. They also work to reduce the coefficient of friction of the car body to zero so that it can move through the air efficiently – think of a sleek race car.

GET FOCUSED

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

• How does the velocity of an object affect the frictional force between it and the surface with which it comes in contact? Frictional force is independent of velocity.

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

• A force is a kind of push or pull on an object.
• Acceleration measures the change of speed of an object that is moving in a specific direction.
• Velocity is a measure of the sped of an object that is moving in a specific direction.

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

LEARN THE LabLearner LINGO

Although there are no new Key Terms introduced in the Investigation 2 Background(s), the Key Terms from Investigations 1 should continue to be used, as appropriate, by teachers and students during everyday classroom discourse.

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 velocity with the class. Remind students that an object’s velocity depends on its speed and its direction.
• Ask students to recall Investigation One. 

• Describe the relationship between the amount of force recorded by the spring scale when pulling the wood block and the frictional force between the wood block and the table. The amount of force recorded by the spring scale represented the applied force because the block was pulled with a constant velocity. In this case, the applied force is always opposite and equal to 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.