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# PreLab

### BRANCH OUT

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

• How does the smoothness of the two surfaces in contact affect the frictional force between the two surfaces?

Note: This question is located in your  SDR at the beginning and end of the Investigation.

### GO DEEPER

As a class, read the Background(s) in the Investigation. When finished, discuss the following concepts as a class:

• The coefficient of friction (μ) is a value between 0 and 1.
• The coefficient of friction describes the degree of interaction between two surfaces.
• A higher coefficient of friction indicates that the two surfaces in contact have a greater resistance.
• A lower coefficient of friction indicates that the two surfaces in contact have less resistance.
• Normal reaction force is the force of gravity on that object when pulling an object across the table (in this case, the woodblock).

### 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 your findings thus far in the Friction CELL by asking the following questions.
• Based on your experiments, what factors affect frictional force?
• Based on your experiments, what factors do not affect frictional force?
• During this Investigation, you will be conducting trials, this time to determine whether or not the smoothness of the two surfaces in contact affects frictional force.
• You will conduct your trials using the same method as was used thus far in the CELL.
• Consider the following questions.
• During these trials, is it important that you pull the woodblock at the same velocity in each trial?
• During these trials, is it important that you keep the mass of the object constant?
• During these trials, is it important that you keep surface area constant?
• Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful in the lab.
• After the video, divide into your lab group to discuss strategy for the lab. For example, you may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow you to anticipate the laboratory experience you will soon encounter. You 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

You should review the Investigation and video in preparation for the Lab.