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 transportation engineers design roads to provide the right amount of friction. They know that friction provides traction and control for a safe driving experience, especially in icy or wet conditions.

GET FOCUSED

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

• What is the relationship between speed, velocity, and acceleration? A change in velocity occurs when an object in motion either changes speed or changes direction. Acceleration denotes a change in velocity in a period of time.

• How does the frictional force affect motion? Frictional force decreases the velocity of an object. That is, it decreases the speed of an object.

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:

• A force is a kind of push or pull on an object.
• A force has two qualities: direction and magnitude.
• Velocity is a measure of the speed of an object that is moving in a specific direction.
• Acceleration measures the change of speed of an object that is moving in a specific direction.
• Acceleration is a change in velocity.

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.

• force
• velocity
• acceleration
• applied force

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

• Explain that this CELL will focus on forces, motion, velocity, and acceleration and that students will perform experiments to better understand how those concepts are related.
• Complete the Recall section in students’ SDRs. 
• Review with students that a force is a kind of push or pull on an object. A force causes an object to accelerate in the direction of the force. 
• Tell students that scientists use a different definition of velocity than people may use in everyday language.
• Walk across the room in a straight line, maintaining a constant speed. 

• Ask the class whether you changed direction while walking. No. 
• Ask the class whether you changed speed while walking. No.

• Tell the class that velocity is a measure of the speed of an object in a specific direction. Since you changed neither the speed or the direction of your walk, your velocity remained constant until you stopped moving.
• Walk across the front of the room again, this time changing direction but still maintaining a constant speed. 

• Ask students whether you changed velocity while walking. Yes. Since you changed direction, you changed velocity.

• Walk across the front of the room again, this time slowing down and speeding up at random intervals. 

• Ask students whether you changed velocity while walking. Yes. Since you changed speed, you changed velocity.

• Tell students that this understanding of velocity will be important throughout this CELL.
• 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.