October 12th, 2016: LAB (): Ballistic Pendulum

Michell Kuang
Lab Partners: Charles, Anthony
Date performed: 10/12/16

Note: This lab was an addition to the original lab manual, which is why there is no number.

In this lab, we try to determine the firing speed (launch speed) of a ball from a spring-loaded gun. To do this, we used an apparatus that allowed us to shoot a ball into a nylon block that is supported by four strings. Once the ball is "absorbed" into the block, it hits a piece of metal that we use as our angle indicator, and that shows the angle at which the ball+block system rise.

Setup of "ballistic pendulum" apparatus

First, we measure the mass of the ball and the block. The ball we used was 0.0073kg +/- 0.0001kg and our block was 0.0806kg +/- 0.0001kg. We also measured the length L from the top where the strings were attached to the center of the nylon block. Our L was 0.225m +/- 0.002m. The "cannon" had three different notches that we could pull it back to fire the ball, and we used the first notch. After recording all this data, we fired the ball and repeated this four times to get an average.

Angles to which the block rose for each run; average angle for all runs

Now that we had this average angle, we used it to calculate our h, which is the height that the ball+block system rose. Using that and all of our measured data from earlier, we were able to determine a firing speed of 5.0568m/s. We calculated the uncertainty for this launch speed as well. Finally, we used this launch speed to find our theoretical (guessed) value of the distance that it would go if we launched the ball horizontally into the air.

 

Calculation of theoretical launch speed and comparison of theoretical distance vs. actual distance

 

Calculations for uncertainty in our launch speed 

Both our guessed and measured values came out to be 2.3m, meaning the actual, experimental launch speed is about the same as our calculated one. This shows that our experiment was a success!