JC+and+Steph

= Clock Design: Simple Harmonic Motion = Date of Publication (Date of Most Recent Edits)

**Participants**: JC Smith, Stephanie Robison **Purpose**: The purpose of this lab is to design and characterize a clock that is makes accurate time measurements in the range of 30 to 90s. **Lab Documents**:



**Brief Description Clock Design**: Our clock was the pendulum design. We attached "bobs" of different masses to test how it would effect the clock. We also used strings of different lengths. To time thirty or sixty seconds with our clock a 20.5cm string is used with a 500g "bob." To start the clock the "bob" is drawn back to 64cm up from the table keeping the string straight. The "bob" is then dropped, and each swing is equal to approximately one second.


 * Specifications of Clock:

Procedure:** 1. Select 500g weight, and adjust string to 20.5cm 2. Attach weight to string 3. Draw string and weight to 64cm off the surface of the table 4. Start timer at the moment the weight is released from 64cm 5. Stop time after ten swings 6. Repeat all the steps above with different weights and lengths of string to collect data for a graph

**Design Variables:** Provide a brief discussion of which variables you think may influence the operation of your clock and how you predicted (pre-lab) that these would influence the performance of your clock.

**Studied Design Variable 1:** One variable that was changed was the length of the string. With the added length, the "bob" will swing at a slower pace and therefore affect frequency and accuracy of the clock. To test this factor, we did a few experiments where the length of the string was changed. We started the string length at 20.5 cm and recorded the data. Then we shortened the string to 19 cm. After we changed the string length to 36 cm, and noted that the time for the clock to get the same number of swings had drastically increased.

**Studied Design Variable 2:** Another variable that was changed was the weight of the "bob." When the "bob" was heavier the pendulum would swing faster, and a lighter "bob" would make it swing slower. This is obviously effecting the frequency of which then effects the accuracy of the clock. To test this we experimented with three "bobs" of different masses. We tested a 500g "bob," a 600g "bob," and a 700g "bob," all with the different string lengths. We recorded what we had observed and noted that the time for the clock to get the same number of swings had changed, but it was not as drastic of a change as the string length changes.


 * Lab Questions **: Write out and answer any questions that are included as a part of the lab.


 * 1. Describe in detail how your device may be used to measure an event that lasts 60s. What would the accuracy of this measurement be?**

This device uses a pendulum motion to measure one swing in one second for sixty seconds. Our specfic device uses a 20.5cm string with a 500g "bob" at the end used as the pendulum. To get the swinging motion, the pendulum is drawn back so that the string is completely straight and 64cm from the surface of the table.


 * 2. Which variable that you studied had the most significant effect on the frequency/period of the clock? If you built your clock with a 20% increase in this variable, what would the new frequency/period of the clock be? Support your answer by referring to data in your report.**

The length of the string had the greatest effect on the frequency of our clock. If we increased the length of the string by 20%, the frequency would decrease.


 * 3. Which variable that you studied had the least significant effect on the frequency/period of the clock? If you built your clock with a 20% increase in this variable, what would the new frequency/period of the clock be ? Support your answer by referring to data in your report.**

The variable that had the least significant effect was the change in mass. This change resulted in only a second or two change in the data, hardly influencing the data at all. If we increased the mass by 20% the frequency would increase.


 * 4. Though it was not a project requirement, it would be nice if your clock could also measure much longer times, on the order of 10 to 15 minutes. Would your clock design still be accurate for long time measurements? What might affect the accuracy of the clock for these longer measurements? Can you think of a way to improve the design to make the clock more accurate for longer measurements?**

Our clock measurements would not be accurate for a period of time as long as 10 to 15 minutes. The biggest effect on the accuracy for this amount of time would be that the pendulum would slow down tremendously. As far as we know, there is no design (from the materials we have) to make the clock more accurate for these measurments because there is no way to keep the pendulum moving at that rate for that long amount of time.

**Conclusion**: We think that the experiment produced a valid and reproducible result because we were able to test the same thing several times and get remotely the same every time. When we would change the mass slightly, the time would change slightly, etc. Our experimental result differs form the actual result simply from human error. We're sure human error occured when dropping the "bob" and starting the timer. It would be awfuly hard to drop the "bob" and start the timer at //__exactly__// the same time, which is an example of possible human error for this experiment. To possibly improve this source of human error we could try starting the timer after one swing so we aren't trying to do both (dropping "bob" and starting timer) at the same time.

**Independent reflection:** One lab report will be turned in for each group. In addition, each student must complete //independently// a reflection addressing the following questions: > > //Don't forget to link to your lab report from the lab reports page and to include a link to your lab report in your reflection.//
 * How was the process of designing and testing a clock similar to the scientific method as discussed in class?
 * How did it differ?
 * What "steps" in the scientific process were present and which were missing?
 * Was there a part of the activity that is not a part of the scientfic process?