> > Car Sliding Across an Ice Rink - Student Activity

# Car Sliding Across an Ice Rink - Student Activity

#### Summary

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This activity guides students through the process of analyzing the motion of a car as it moves across an ice rink and then rapidly decelerates as the brakes are pressed. In addition to one dimensional kinematics, the worksheet prompts students to consider both the frictional force and measurement uncertainty.

## Learning Goals

Students will:

• Carefully observe a video
• Measure the displacement of the car at certain times
• Calculate the initial, final, and average velocity of the car
• Calculate the average acceleration of the car
• Calculate the uncertainty in their measurements
• Consider the origin and direction of the frictional force on the car
• Suggest a reason why antilock brakes are better.

## Context for Use

I use this activity with my students at the beginning of the unit on forces as a way to re-emphasize 1D kinematics but at the same time to get them thinking about forces, friction, and measurement uncertainty. Although it's quite highly scaffolded (giving the students quite detailed instructions) the instructor may need to offer additional information about forces and friction and uncertainty if the students haven't seen them before.

The instructions don't prompt the students to make graphs of the motion, but instructors may want to have them do it anyway. If students don't make graphs the activity takes about an hour to complete. If graphs are made, an additional half hour is required.

## Description and Teaching Materials

Video files: Car or person sliding across an ice rink

Here is a worksheet (Microsoft Word 2007 (.docx) 2.2MB Aug30 14) to guide students through this activity and worksheet solutions (Microsoft Word 2007 (.docx) 2.4MB Aug30 14) for instructors.

These instructions are highly scaffolded, giving students step-by-step instructions. An instructor may chose to provide less detailed instructions to encourage independent thinking and problem solving.

## Teaching Notes and Tips

The instructions don't prompt students to graph the motion, but the instructor may want to have them do it if there is time.

When I made my measurements I tried to be as accurate as possible and estimated my uncertainty to be about 5 cm of displacement and 1 frame of time. The uncertainty in the measurements of some students may be larger.

## Assessment

The Person Sliding on Ice activity could also be used as an assessment for this activity. They are very similar in terms of the physics, but have different numerical values.

## References and Resources

Here is the Hyperphysics page on Friction and Automobile Tires

Here's a "How Stuff Works" link on Anti-lock breaks