Rubber Band CarBy richie tIerney and andrew robinson
What are rubber band cars?
Rubber band cars are cars that have two wheels, and those wheels are CD's. It is attached to the car by a stick which acts as an axle. A rubber band is wrapped around the stick, and when let go, the rubber band unwinds and it spins the stick, which makes the CDs spin. The body of the car is made off cardboard, and we could modify the shape. We were given 2 CD's, 1 piece of cardboard (dimensions are 5x5 Inches), 1 rubber band, and a stick. These were the materials for the basic car.
Elastic Potential Energy
The way that elastic potential energy is created is by winding up/stretching the rubber band to the max point. By letting the rubber band go the potential energy is turning in to kinetic energy because of the wheels creating friction against the ground and getting the car to move. Kinetic energy is the energy that comes from the car moving through the wheels, or anything that moves. Potential energy is the energy that is possible kinetic energy, but it is not currently being used. Elastic potential energy is the energy that comes from the rubber band being stretched and pulled around the stick.
The longest distance one of our cars went was 62 feet, and it was after multiple attempts of getting 55 feet.
One important modification that we made to our car was finding the best rubber band. The best rubber band that we found was a thinner, longer rubber band. It was just wide enough so it would not break when you wound it up many times, and when you would release the car, it would take a longer time to fully unwind. It also made the car go faster at the end, giving an extra burst of speed. This modification made us go from around 30 feet, to around 60 feet.
2. Another important modification we made to our rubber band car was adding a stick to the end of the car. By adding a stick to the end of the car, the end of the car was not dragging. Since we added a stick, it removed friction which allowed for the car to go farther and faster. Also by adding the stick to the end, we were able to cut the rubber band and tie it to the stick. When we did this, it increased the potential energy by increasing the amount the rubber band could stretch, thus creating more kinetic energy.
3. A third important modification we made to our rubber band car was adding rubber bands to the outside of the CD's. By adding rubber bands to the outside of the wheels it created more friction (traction), which makes the CD's have a better grip on the ground. When the wheels have a better grip on the ground, it makes the car be able to go farther and faster easier than without them there.
4. Another important modification we made to our car was taking off the wings we added from cutting the body of the car. Adding the wings adding more weight because we had to tape it down. When we removed the wings and cut more off, the car had less weight to pull, which allowed for it go faster and farther. When we made this modification, it made our car go from about 20 feet, to about 30 feet on average.
Video Physics App
To get the velocity and acceleration we used an app called Video Physics. In this app, you take a video of your car, and plot points on the video. The dots represent where the car was on a certain time. You can plot the dots yourself, or you can make the dot plotter fit around the wheel, and hit track. When you do the track method, it takes less time, but it is not always as accurate. You had to bring a meter stick so you could tell the app how long a meter is. The formula is y1-y2 over x1-x2.
Making the video, we had to film it from far enough back because you needed to get the whole car in the frame, and you also needed to get the meter stick in frame. We made the graph by plotting the points, the app put together a graph of velocity.
By putting the points (.75,1), and (1,2), we got the acceleration to be .25 mps squared.