Physics&Ballet - How to measure data accurately
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Physics&Ballet - How to measure data accurately
Hi - my project is on how can I apply laws of physics to improve my pirouettes at ballet. I’m focusing on abt 5 main physics principles. To test if increasing understanding of physics can improve pirouettes I’m asking ballet friends to do a pirouette (blind - they don’t know why - to set a baseline) then I tell them abt one law of physics and how it applies to a pirouette - and then I have them do 3 pirouettes and focus on that 1 law. My data from this is pretty subjective - I ask the teacher to comment on the before vs after and I ask each subject to comment on their before vs after. Is it scientific to measure subjective opinions of their performance? I don’t know how to quantify it. I wish I could measure the difference in turn speed or the difference in angle of their axis. But don’t know how and don’t have time. Is subjective observation by a professional ballerina and the subjects enough to count as scientific? It’s my projects biggest weakness. Thank you for your help.
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bfinio
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Re: Physics&Ballet - How to measure data accurately
Hi - I don't really know anything about ballet, and it may be up to your teacher/science fair as to whether evaluation by a professional would count as a quantifiable variable. But I can make a suggestion for a quick way to take measurements that you might have time for:
1. Use a phone to take a video of each pirouette. If possible use the slow-motion mode (most newer phones have this). This records the video at a higher frame rate, or number of frames per second (fps), than a regular video. You will need to Google it for the phone you're using, but "normal" video is usually 30 or 60fps, and "slow motion" video is usually 120 or 240fps.
2. Play the video back and count how long in seconds it takes for the person to complete one full revolution (360 degrees). How exactly you do this depends on the software on your phone or the computer where you transfer your videos. Some software might show a timestamp a format like h:mm:ss.ss (hours, minutes, seconds, tenths and hundredths of a second), so you can subtract the seconds when the spin starts from the seconds when the spin ends to calculate the duration of the spin. Other software might let you step through the video one frame at a time, so you can calculate the duration based on the number of frames. For example, if your slow motion video is 240 frames per second, and the spin took 120 frames, then it took 120/240 = 0.5 seconds.
4. You can use this time to calculate rotational speed with the equation
angular speed = angle (degrees) / time (seconds)
In this case the angle is 360 degrees for one full revolution (or whatever you counted in the video, I don't know exactly what a pirouette is) and the time is the time you measured in step 2.
5. You could also use the video to measure angles (again not knowing exactly what a pirouette is I don't know exactly what axis you're referring to). One very simple low-tech way to do this is to pause the video and hold a protractor up to the screen to measure an angle. There are also various video and image analysis programs that will let you click pixels on the screen to measure distances and angles to do this more precisely. ImageJ and Tracker are two such programs that I'm aware of:
https://imagej.net/ij/
https://physlets.org/tracker/
Hope all of that helps!
Ben
1. Use a phone to take a video of each pirouette. If possible use the slow-motion mode (most newer phones have this). This records the video at a higher frame rate, or number of frames per second (fps), than a regular video. You will need to Google it for the phone you're using, but "normal" video is usually 30 or 60fps, and "slow motion" video is usually 120 or 240fps.
2. Play the video back and count how long in seconds it takes for the person to complete one full revolution (360 degrees). How exactly you do this depends on the software on your phone or the computer where you transfer your videos. Some software might show a timestamp a format like h:mm:ss.ss (hours, minutes, seconds, tenths and hundredths of a second), so you can subtract the seconds when the spin starts from the seconds when the spin ends to calculate the duration of the spin. Other software might let you step through the video one frame at a time, so you can calculate the duration based on the number of frames. For example, if your slow motion video is 240 frames per second, and the spin took 120 frames, then it took 120/240 = 0.5 seconds.
4. You can use this time to calculate rotational speed with the equation
angular speed = angle (degrees) / time (seconds)
In this case the angle is 360 degrees for one full revolution (or whatever you counted in the video, I don't know exactly what a pirouette is) and the time is the time you measured in step 2.
5. You could also use the video to measure angles (again not knowing exactly what a pirouette is I don't know exactly what axis you're referring to). One very simple low-tech way to do this is to pause the video and hold a protractor up to the screen to measure an angle. There are also various video and image analysis programs that will let you click pixels on the screen to measure distances and angles to do this more precisely. ImageJ and Tracker are two such programs that I'm aware of:
https://imagej.net/ij/
https://physlets.org/tracker/
Hope all of that helps!
Ben