Altwood's Device Lab
By: Jake Williams
April 21, 2014
Purpose:
The main objective for this lab is to derive an equation for the acceleration of the masses of Altwood's device and include Full Body Diagrams for each mass.
Theory:
Altwood's Device is a great example for using Newton's third law of motion which states, "when one object exerts a force on a second object, the second exerts a force on the first that is equal in magnitude, but opposite in direction." This states that acceleration will remain equal when mass #1 goes up and when mass #2 goes down. To find these accelerations, there will be 3 trials and the derived equation that will be used as well as the kinematic equations and compare:
Altwood's Device is a great example for using Newton's third law of motion which states, "when one object exerts a force on a second object, the second exerts a force on the first that is equal in magnitude, but opposite in direction." This states that acceleration will remain equal when mass #1 goes up and when mass #2 goes down. To find these accelerations, there will be 3 trials and the derived equation that will be used as well as the kinematic equations and compare:
Experimental technique:
To conduct this experiment, I used an Altwoods device, landing carpet(to soften the contact point), a stopwatch, and weighted coins in grams.
Data:
What remained the same throughout this experiment was the height of 50.9cm.
After I conducted the three trials using a stopwatch and the weighted coins, I organized it into a spreadsheet using Microsoft Excel. After I found the times, I found the average of all three trials and found an outcome of 0.9s overall.
Analysis:
The last step to accomplish was plugging the weight in coins and multiplying it by gravity to get the overall acceleration using the derived equation.
Data #1:
Data #2:
Data #3:
Now for the Kinematic equation work:
-50.9cm was converted to .509m
Data #1:
Data #2:
Data #3:
Conclusion:
The results are relatively similar compared to using the derived equation and the kinematic equation. This portrays that our calculations and measurements were not too far off from getting the same answers. The first two calculations resulted to be 1.96m/s squared and 1.59m/s squared making it only .37m/s squared off. I feel the derived equation is more simple since it only asks for the two masses and multiplying it by gravity, but the kinematic equation is more complicated asking for the seconds and distance (which may have more probability of error). The major contributors to the difference in the accelerations can include an inaccurate time or not a precise measurment of distance. The distance could also vary with the two weights on the string. The longer the string, the harder it would hit the landing carpet. I reduced error to the best of my ability by making sure the distance was the same for each time experiment and made 3 trials for each experiment to find the average. I also made sure the weights in grams were not too far apart from each other to restrict from clicking the stopwatch too fast. The goal was for at least 1 second for each drop. I also feel error was reduced when I used the stopwatch instead of the laptop to record a video, because judging of how many frames you counted while recording, could affect the time drastically. The old-fashioned way seemed to be more realistic. Overall, the goal was to have the accelerations be as close possible and I feel it was accomplished under good circumstances.
References:
http://lahsphysics.weebly.com/atwoods-device-lab.html
http://Devinsaysphysicsisaverb.weebly.com
http://fishingisphysics.weebly.com/