Rubber Band Car Project By Brandon THOMAS and david murphy

Introduction

The Rubber Band Project is a project where each group is tasked with creating a car powered by a single rubber band. Each group is given card board, used as the chassis, a wooden skewer, used as the axel, CD's, used as the wheels, and duct tape.

The Cardboard

The Corrugated Cardboard was used as the main chassis of the car, which held the axel connecting the wheels. The default body of the car was created by making a 2 by 1 and 1/2 incision on the side of the cardboard where the corrugation runs lengthwise.

The CD's

The CD's that were given to each group were used as wheels, and each wheel had to be attached as to be securely fitted to the axel of the car.

The Wooden Skewer

The Wooden skewer was used as the axel, being placed through the cut in the cardboard and through the holes of the corrugated cardboard, as to reduce the amount of friction as the car moves.

How does the car move?

Each car that was built moved by elastic potential energy turning into kinetic energy. Elastic potential energy is potential energy stored by the stretching or pulling of a spring, and in this case the spring being the rubber band. Kinetic energy is the energy that an object or thing has in motion. The Elastic potential energy that was stored by winding up each rubber band turned into kinetic energy when the tension and potential energy in the rubber band was released. When the tension was released from the rubber band being wound up around the axel, the potential energy that was stored in the rubber band was released, and turned into kinetic energy, and moved the car forward.

Important Modifications

Even though each group was given a basic default car to start with, there were still a lot of modifications that could be done to change certain aspects of the car. These modifications had to do with what type of rubber band was used, the shape of the cardboard, the location of the axel, etc.

Modification #1

Rubber bands on the wheels

One of the most significant changes we made to our car was putting the thickest variant of rubber bands around the edge of the wheels, to create more friction against the ground. One of the biggest problems our car had before this modification is the wheels kept spinning out before they had enough friction against the ground to create momentum and start moving the car forward. After this modification, our car went a total of 22 feet, up from our previous record of 17 feet.

Modification #2

Long, thin rubber ban.

The second important modification we added to our car was the use of the long, thin rubber band as opposed to other thicker or shorter options. As we tested the different types of rubber bands available we found that short rubber bands released their energy too quickly to be able to carry the car a long distance. In addition to this, when we tested the thicker rubber bands, we found that although they are strong and have the most amount of Elastic Potential Energy than any other rubber band, they release that energy too quickly, and do not carry the car far enough. The long thin rubber bands, when wound up, release their potential energy at a slow rate, and move the car a much farther distance, with this modification, our car went 27 feet.

Modification #3

Skewer out the back

Another important modification we added to our car was the skew that came out the back of the car. This helped the car by not only helping the car become centered and balanced, but also help the rubber band have more tension and more elastic potential energy. Before the skewer was added at the back, the rubber band was attached to the cardboard itself. Not only does this create less kinetic energy, it also creates a situation where the car easily can turn and not go in a straight line. In addition to putting the skewer in the back, the rubber band was cause as to be one straight piece of rubber as opposed to a loop, so it could be wound up more around the axel and turn into more kinetic energy over a longer period of time. With this modification, our car went 34 feet.

Modification #4

Stable Wheels

The Final modification we made to our car was wrapping duct tape around the parts of the axel were the wheels were located, so the skewer could tightly fit in the center hole of the CD. Before this, we were attaching our wheels by putting tape on the surface of the CD and sloppily attaching that to the skewer. This was not optimal, as the wheels were all too often crooked and did not go straight. After we made this modification, our wheels were stable and are car almost always went straight. After this modification, our car went 39 feet.

This is a picture of our best car, that went a total of 39 feet.

Velocity and Acceleration

With each of our cars, we were tasked with finding the Velocity and Acceleration of the car when it moved. Velocity is the speed of an object in a direction, while Acceleration is the increase in rate or speed of an object in a negative or positive direction. To figure out the velocity and acceleration, we used the video physics app. The video physics app takes a video and by graphing points throughout the duration of the video, uses those x and y values to calculate velocity and acceleration. The formula for velocity is change in position over change in time, and the formula for acceleration is the change in velocity over change in time.

Above is the video used in the video physics app in order to calculate acceleration. The video required the angle of the shot to be perpendicular to the movement of the car, so the car wouldn't be going diagonally in the shot. This is because when the shot was aligned like this, it was easier for the app to track the object and accurately calculate the acceleration and velocity of the object. We made the graph by graphing points on the location of the car at certain intervals, and then those points would be used in a graph to show where each point was at each time it was graphed. In addition to this, a meter stick was put in the shot, so the graph could be calculated in meters.

This is the graph of the velocity of our car. The graph shows that the car starts gaining velocity quickly, but then it start's to slow down as the time increases. Each point on this graph is a point graphed in the video. At around 4 seconds, that is where the car starts quickly losing velocity.

The acceleration of our car is 0.4/2.75 meters per second squared. We found this number by finding to points on the graph, and finding the change over velocity over change in time. Our change in velocity was 1 - 1.4, and our change in time was 0.5 - 3.25. This came out to 0.4/2.75 meters per second squared.

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