# Investigating Speed and Constant Acceleration

#### Summary

Students roll miniature cars down a ramp and measure their speed and acceleration every 10 cm. Students can vary the type of car, height of ramp or the ramp material. Student change one of these variables to investigate how the car's speed and acceleration change. Speed and acceleration can be graphed. The speed of each car during any one trail should increase linearly but it's acceleration should remain constant. The graphs can be compared and the slope differences discussed.

## Learning Goals

Students learn to vary only one variable. Students investigate the relationship between charts and graphs. Students model constant acceleration. The key vocabulary words are speed, constant acceleration, variable, and slope.

## Context for Use

This is a lab that should take two 45 minute periods. Groups of 2-4 should be used. Students should be familiar with plotting points on a graph.

**Subject**: Physics:Classical Mechanics

**Resource Type**: Activities:Lab Activity

**Grade Level**: Middle (6-8)

## Description and Teaching Materials

Students are given a ramp (board, rain gutter, car track, etc.) about 1 meter long, a way to elevate one end, (books, ring stand, etc.) and a small car. Students experiment rolling a small car down the track. Several variables can be investigated: height of ramp, type of car, and ramp material. This is an informal investigation at this point. Most students will be trying to find the fastest car. Allow 10 - 15 minutes for the students to "play" with the equipment. Have students write down their findings and present them to the class. Example: Our group found that the rain gutter seems to be the fastest ramp. Groups may have several findings and some of them may not be true. These will serve as possible investigations in part 2 of the lab.

Have each group of students choose a variable they would like to investigate. Mark the ramp in 10 cm intervals start at the raised end. Students should find the the speed of the car at each of these marks, do just one mark at time. After completing 5 - 6 points they should change the variable they would like to investigate. Measure as before and change the ramp for a third time. (Students might be able to produce a procedure to measure speed.) Acceleration can be found for each of the distances. Students should then graph the speed of each trial on the same graph and the accelerations on a different graph. Have students compare and contrast their graphs with other groups and present their findings to the class.

Have each group of students choose a variable they would like to investigate. Mark the ramp in 10 cm intervals start at the raised end. Students should find the the speed of the car at each of these marks, do just one mark at time. After completing 5 - 6 points they should change the variable they would like to investigate. Measure as before and change the ramp for a third time. (Students might be able to produce a procedure to measure speed.) Acceleration can be found for each of the distances. Students should then graph the speed of each trial on the same graph and the accelerations on a different graph. Have students compare and contrast their graphs with other groups and present their findings to the class.

## Teaching Notes and Tips

If the ramp is too vertical the car will crash when it reaches the bottom. Have students limit the angle of the ramp to about 30 degrees. Times can be very short for some of the distances. Students may want to make several measurements at each interval and choose the best. An average could be used but often one of the times is way off and should be thrown out.

## Assessment

Students will give two classroom presentation. The students will also produce two graphs

## Standards

Grade 6 - Physical Science III.F.4 - the student will use a frame of reference to describe the position, speed and acceleration of an object and the student will measure the speed of an object.