Post #2: Garage Door Acceleration

 

 

I was thinking of what to do for my next physics post when I came home.  As soon as the garage door opened, I realized that the answer was right in front of me! The garage door opening or closing demonstrates acceleration! Unfortunately, I can't find the acceleration without the elapsed time or the velocity, because the formula for acceleration is a=v/t. First, I took a video of the garage door closing and found that it took about 14 seconds to close completely.  Then I took the height and found that it was about 8 feet, or 2.43 meters, since the door only went down, the displacement is also 2.43 meters. Using this information, I could find the velocity, v=2.43m/14s, v=.17 m/s. Since I have my velocity and my elapsed time, I can now find the acceleration of my garage door!
a=.17 m/s /14, a=.012 m/s^2. Wow, that's a fast door!

Using physics, I was able to discover the acceleration of my garage door. First, I needed to find the velocity, which was accomplished by finding the displacement (2.43m) and the time (14s). Then I was able to plug these numbers into the equation for acceleration.

Swimming in the Pool: Distance and Displacement

me entering the pool

Today, I went swimming in my pool. I began by the steps on the right of the picture and swam to the end of the pool on the left. I count one lap as going to the end and coming back. After I did five laps in the pool I got out.  I started at about 4:55 and stopped at 4:57 with 10 seconds left.  So it took 130 seconds.  The length of my pool is about 27 feet, or 9 meters.  In physics, I learned that distance is the magnitude, or the amount of the displacement.  Therefore, one total lap is equal to 9m*2, and 5 laps is equal to 5(9m*2), which is equal to 90 meters.  Since I calculated the distance, I can plug it in to the formula we learned in class for average speed.  The formula is distance/time=speed. 90 meters/130 seconds=.69 m/s. So I swam about .69 meters per second.

I could also use this data to find my average velocity. We learned that the formula for average velocity is: displacement/time=velocity.  Displacement differs from speed because it is the "shortest path from the initial to the final position of the object's motion." In order to find my displacement, I used the formula: x final-x initial=displacement.  Therefore, the displacement for one lap is equal to 9m - 9m=0m +/- .  0m/130 seconds=0 m/s +/- . My average velocity is 0 because I had 0 displacement due to just swimming back and forth.

Physics taught me that velocity is different from speed because velocity includes the speed and direction of the object's motion.  Swimming laps in the pool proves that speed and velocity are different. By finding the length of the pool and the time it took to swim 5 laps, I was able to gather the data necessary to calculate both speed and velocity.