Activity
Simply display each of the car design options for the students to choose from. Next a brief explanation about how the car cannot move unless an external force acts on it and that the different orientations of the bottle on the car change the force that acts on it. Finally after each student has chosen their car simply measure out 10 ft. for which you can time the cars. Give the student one Mentos while the instructor inserts another Mentos in the inside of the squirt bottle nozzle. Remove the original cap from the Diet Coke and have the student begin to countdown with the instructor. When the count down is complete the student will drop in the Mentos and the instructor will quickly screw on the nozzle (in the closed position). Once it is screwed on securely release the nozzle and the reaction inside the bottle will propel the car forward. Make sure to time how long it takes for the car to travel 10 ft. so that the students can then calculate their car's velocity!
Here is a sample activty sheet that can be used:
Here is a video of one of our cars in action!
Key Concepts
This project illustrates many key physics concepts. The first is the concept of velocity. Velocity is a measure of displacement (change in position) with respect to time. When the car travels 10 feet, the velocity is measured by dividing the 10 feet by the amount of time required to travel that distance. Another concept introduced in this project is Newton's Laws of Motion, specifically the first law. The first law states that an object at rest will stay at rest unless an external force acts on the object. In our activity the object is the car and the external force acting on it is the Diet Coke and Mentos reaction. Finally, students are introduced to the idea that angling the spray of the soda will affect the performance of the car. The purpose of the activity is not to teach the details of each of these concepts but simply to get the students to recognize that many important factors must be considered when performing even a simple task such as making a car move from a resting position.