Overview
Phone Pendulum What to turn in Photo + description of your set up Answers to the questions Dataset (labeled) you can submit these as a pdf or google sheet Graph (labeled) you can submit these as a pdf or google doc Group Roles Team Roles Please choose roles in your lab group and indicate who will be doing each task. If your group has less than 4 people you can have more than one role. Role Name Director - Coordinates the lab, makes sure all instructions are followed. Technician - Sets up the experiment, records the data and distributes it to the group Graph Creator - Creates and labels the graph Explainer - This person writes the responses to the questions after discussing with the team. Setting Up Objectives: Set the phone up as a simple pendulum, then use the accelerometer that is built in the phone to study the simple harmonic motion of the phone. Refer to the slides from Ch 14 on pendulums. Recall that the angular frequency of a pendulum can be expressed as where L is the length of the pendulum.ω = 𝑔/𝐿 Equipment: For this activity you will need 1. A smartphone or tablet 2. The phyphox app, available for free for both Apple & Android phones, from their respective stores. 3. A bag that can hold your phone and tie to a string. A ziplock would work. 4. A piece of string that is at least 80cm in length 5. (optional) Another device to remotely access your phone Designed by Miriam Simpson 1
Prepare: Watch the short (4:28) video before you start on this activity to get the basic idea: Play: In the Phyphox app, open the “acceleration with g” sensor. Have everyone in the group (that can) install the phyphox app on their phone, and do a couple of trial runs (carefully swinging your phone and looking at the data). Determine the x, y, and z axis Think: Some questions before you take your data: 1. Draw a picture of your phone and label what you think the x, y, and z axis are (similar to the image above, but the axes may not be in the same places). 2. You should have three graphs (x, y, and z), which one should you use? 3. What do you think will happen to the period when you change the length of the string? 4. Do you think the period will depend on the mass of the phone? Taking Data Check/Calibrate: 1. In the Phyphox app, open the “acceleration with g” sensor. (On your computer, you can use a browser to remote access the Phyphox app). 2. Put the phone in a bag. If the bag does not fit the phone perfectly, you can wrap an elastic band on the outside of the bag around the phone. 3. Try to place/wrap the phone in a way so that when the bag is hung by a string, the phone stays vertical. (If you lost remote access at any point during the process, try operating the phone through the bag or taking the phone out from the bag and repeat.) 4. Use a piece of string that is about 1 meter long. Tie one end of the string to the bag. Pull the string tight. Measure and make five marks on the string that are 30 cm, 40 cm, 50 cm, 60 cm, and 70 cm away from the center of the cell phone. 5. Hold or tie the string at the 70cm mark firmly to an object that is high enough so that the phone will not hit the ground or any other obstacle. 6. Wait for the phone to stop spinning. Displace the phone from its equilibrium position by a small angle and then release, so that the phone starts swinging in a small angle. 7. Calculate the period by measuring the length of time for one cycle. ○ This should be relatively consistent so get a better measurement by calculating the time for 10 cycles then dividing time by 10 ○ Check this by just timing one cycle with another phone or stopwatch ○ If these values do not match you need to stop here and troubleshoot. 2
Record Data: 8. After the motion of the phone appears regular, start an “acceleration with g” measurement with remote access. Count to a total of 10 full oscillations, and then stop the measurement. 9. Count how many periods are shown on the X / Y / Z accelerometer readings. You will notice that one of these axes has about twice more periods than what you counted. Identify this axis on the phone, and explain why the acceleration on this axis reaches maxima twice as frequent. 10. Set the phone on a small angle swing first, after the motion of the phone appears regular, start an “acceleration with g” measurement. Stop the measurement after more than 10 full oscillations. Export the data as a csv file. 11. Repeat Step 9 with string lengths of 60cm, 50cm, 40cm, and 30cm. 12. Open a blank Google Sheet in your Google Drive (you can also use excel) and record string length and period. Analyze/Graph Data: 1. Use excel or sheets to calculate the square of the period. 2. Make a scatter plot of the square of the period against the length of the string. Find the gravitational acceleration using your plot. You may find it useful to refer to this video ● Click on the top of the column with the Period Squared values, ● Click and hold the Ctrl key and click on the top of the column with Height (cm) values, ● Release Ctrl key and open the Insert menu and select Chart, ● The Charter Editor will open. In Setup choose Chart Type > Scatter Chart, ● Make sure X-axis indicates Period Squared (s2) ● Make sure Series indicates Length (m) ● In Customize > Chart & axis titles add axes titles with units to your graph. ● Fit the data to an equation and display the equation on the chart Literally my favorite teacher, love you simpson <3 Questions 1. How does the g relate to the slope of your graph? 2. Would changing the mass in the bag change the period? Try this yourself if you are not sure. 3. What other quantities can be determined with the same experimental design? 4. What can be done to reduce the uncertainties at no cost while staying at home?