Background

        Pendulums are used a lot of the time for grandfather clocks and to keep track of time. The pendulum swings back and forth constantly and is usually used to keep track of seconds. The grandfather clocks got their names from a pop song in 1875 where the artist referred to the clock as “taller by half than the old man himself”.  As technology advances, we use these clocks less and less so they are becoming more of antiques. Pendulums are not only used for keeping track of time, they are used to detect earthquakes, measure how fast a bullet is going, helps buildings to resist earthquake shaking, and it helps robots keep balanced. One example of making a building earthquake proof is in Taiwan, in the Taipei 101 where there is a 726 ton pendulum that keeps the building sturdy.The only problem with the Pendulum is that they run solely on how well the pendulum is balanced. So we were trying to see how we can manipulate the frequencies of which it vibrated.

Problem

        What we are trying to collect is the frequencies of the pendulum’s seconds/vibrations. We measured this to figure out what caused the pendulum to speed up or slow down. We measured that by holding the bob parallel to the table and as releasing it starting the stopwatch. We let it go for three vibrations and when it got back to the original place we stopped the watch and divided how many seconds it took by the number of vibrations which was three.

Hypothesis For String Length

        When the string length is shortened, then the pendulum's frequency will get faster because there is less distance for the pendulum to travel. So the frequency will get larger because if there is less distance to travel the pendulum is getting back and forth much faster.

Hypothesis For Mass Of Bob

        If you add more weights to the bob then it will get faster because there will be more gravity pulling down the bob. This is because the heavier something is the faster it gets pulled to the ground for example if you throw a brick of a ledge and then a feather the brick will go down a lot quicker because it is affected more by gravity than the feather.

Experimental Design

a. Materials

In this lab, we needed the following materials: two ring stands, string, six fishing weights, a stopwatch, and a calculator to measure the frequencies. The independent variable for the first experiment will be the string length and the dependent variable will be the number of vibrations a second. For the second experiment, the mass of bob is the independent variable and the vibrations per second are the independent variable. The constants or the controlled variables for the first experiment are the launch angle, the mass of bob, the number of vibrations, and when you stop and start the stopwatch. For the second experiment, the constants are the launch angle, the string length, when you start and stop the stopwatch, and the number of vibrations you calculate. You want to keep these variables constant because if you are changing them throughout the trials the data will be inaccurate and you would not know what is making the dependent variable change because that would basically be like having many independent variables.

b. Activity Procedure

        As one person let goes of the bob the next person starts the stopwatch as it leaves his hand. We will wait for it to go back and forth for 3 vibrations and when it gets back to where we let it go we stop the watch. We will then take the number of seconds it took and divide it by the 3 vibrations to find the frequency in vibrations per second.

c. Diagram

Results

        a.Observations

        During the string length, I observed that every time that we cut the string length the frequency would get more and more. What I realized while conducting the mass of bob experiment I realized that the data wasn’t varied at all. For example in the string length lab when the string was 58 cm it had a frequency of 0.56 vibrations per second, and when the string was 20 cm it had a frequency of 0.8 vibrations per second. During the mass of bob lab when the bob had 2 weights it's frequency was 0.56 vibrations per second and when it had 6 weights it had the same exact frequency at 0.56 vibrations per second.

• Place string on the bar.
• Place 3 weights on the paper clip.
• Pull back string horizontal from the table.
• Start stopwatch once the pendulum is released
• Let the pendulum go for three vibrations and then stop the pendulum
• As the same rope length is being used the data should be around the same if you are doing it correctly
• Complete this process three times before moving on
• The frequencies were measured by dividing three by how long it took to do three vibrations

String Length Data Table

Bob Mass Procedure

• Place 50 cm string on the bar.
• Place how many weights you are measuring on the paper clip.
• Pull back string horizontal from the table.
• Start stopwatch once the pendulum is released
• Let the pendulum go for three vibrations.
• Stop the timer after the third vibration and then measure your data. All of your data for the same measurements should look very similar.
• Do the same test four times per weight. Measure the frequencies by dividing three by how many seconds it takes to get 3 vibrations.
• Do 4 trials for each weight and after each set add two more weights.

Bob Mass Data Table

Conclusion

        After doing the string length lab I concluded that my hypothesis was supported because everytime we shortened the string vibrations per second would go up. This is because the shorter string provides a smaller angle for the bob to move and the smaller the angle is the faster the bob moves^[1]. Then after my mass of bob lab, I realized that my hypothesis was well off from what actually happened. I thought that as more weights were added it will go faster but it ended up that the frequency stayed constant throughout the whole experiment. The mass doesn’t affect the frequency because the mass and force are proportional so when you change the mass the force stays proportional with the weight^[2].

        This lab we worked on helped us to get used to what we were expected to do in eighth grade. We also worked on doing labs as a team, evenly distributing jobs, and trying to get the most done in the least amount of time. The greatest challenge we had in this lab was that a lot of the times for the mass of bob we would miscommunicate and drop the string before the timer was starting which made the times all over the place. Another thing that we worked on in this lab was putting our data into an organized table so it could be easily analyzed.

        The most important thing we learned during this lab was how to measure accurately and how we converted the amount of time it took for 3 vibrations to the frequency. I found this important because we are learning how to ^[3]take two different variables and turning them into one so they are easily compared to the other data.

        What I concluded from this is the shorter the string is on the pendulum the faster it will go because there is a lesser angle for the bob to travel through. From the mass of bob lab I now understand that the mass of the bob is not a factor in the speed of the pendulum because the mass and force are proportional and if you bring the mass up the force goes up too but they rise the same amount so the frequency isn’t affected.

Pendulum Lab Grading Guide: Procedure Maximum 3 pts each/Data Table Maximum 4 pts each

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