Physics Journal #1: Velocity and Acceleration

This picture was taken before I went to Titan Motorsports's "The Weekender" to watch my friend's car participate in the loudest exhaust challenge and to try to score some deals on parts for my car. If you consider my friend, the photographer, as the origin or the position sensor in our lab, my car is actually travelling at a negative velocity because velocity indicates both rate of motion AND direction, and can be found by dividing the total displacement by the time elapsed. My car is not slowing down as one might expect with a negative velocity, in fact it is maintaining a constant velocity, the velocity is negative because my displacement is negative since i started in the positive direction and drove toward my friend so he could take the shot.

As car enthusiasts, we constantly brag about our car's acceleration, and the people at the event were no different, but when everyone was talking i realized how often we misuse the term. Acceleration describes the change in velocity over time, so it includes both flooring the gas pedal, as well as depressing the brakes. Acceleration, which people do not realize, can also be a negative amount because it is derived from velocity, so either speeding up in the negative direction (like in the picture) or slowing down in the positive direction, like stopping at a stop light, yield a negative acceleration. Therefore positive acceleration can be derived from stepping on the gas pedal and going in the positive direction, as well as applying the brakes in the negative direction. So when we strapped our cars to the dynamometer to measure horsepower and torque, although the car's speedometer can register the speed the wheels are spinning at, techincally the car is neither accelerating nor achieving a change in velocity since there the car is staying in the same spot. At the end of the event, i drove home and after arriving i realized that while I had driven from town to Aiea and back (which was clearly indicated by the amount of gas i had left in the tank), my displacement indicates i actually had not moved at all, and therefore my average velocity and acceleration was 0, which was slightly disappointing.