Making and analyzing a motion analysis (or kinematic) video with your students is a great way to engage them. To avoid wasting too much time during the realization, here are 7 simple tips to follow to ensure that these videos are quickly usable.
1. A smartphone is enough
As the saying goes: "The best camera is the one you have with you". There is no need to shoot in 4K to obtain usable videos for motion analysis. Virtually all laptops are able to film in 720p format, a resolution of 1280x720 pixels, which is already very much enough. All your students with a mobile phone will therefore be able to film a sequence that they can analyze.
2. Use a tripod or a stand
Video motion analysis consists of analyzing the movements of an object on an image to infer the movements in the real world. If the camera moves during video recording, this movement will be interpreted as a movement of the object and therefore cause errors in the relative position of the object in the frame. It is therefore important that the camera plane is fixed during the duration of the recording, ideally by fixing the camera on one foot. You can also place the device on a table, a window sill and wedge it well so that it does not fall. If the device is held by hand, you must alert the cameraman not to move and especially not to follow the moving object!
3. Add a scale
To be able to calibrate the size of objects on the screen and to their dimension in the real world, we need a scale; that is, an object whose size we know and which will appear on the video at the same time as the movement we want to analyze. It is best to use a meter, but you can also use a character or object whose size you know. Be careful, the scale and the indications of which compote must be readable on the video.
4. Check the distance
For a motion analysis video to be usable, all positions of the moving object must be at the same distance from the camera's lens. In practice, there will always be variations in distance during movement, but it is appropriate to try to minimize them as much as possible. For example, one will try to position oneself further away rather than closer, using optical zoom, or digital zoom if the resolution is not too compromised. Also, be sure to place the scale at the same distance from the lens as the moving object.
5. Facilitate the pointing
To achieve a good result, the object or part of the moving character that you want to analyze must be clearly identifiable. If the object is too small, we will make sure that it is large enough to be clearly visible on the screen. On the contrary, if the object or character is wider, a distinctive sign will be placed that will serve as a reference for the entire pointing sequence. Also remember to work on the contrast between the background and the object so that it stands out better on the screen. A uniform background is often preferable.
6. Adjust the FPS (Frames per second)
The cadence or FPS is the number of frames per second that are captured by the camera. The greater the cadence, the sharper the image of the movement will be, but in return, the less good the resolution of the image will be. For relatively slow movements, a rate of 30 or 60 frames per second is sufficient (the default rates of smartphones). If the movement is fast, a too slow rate will give "bave" images it will not be possible to make a precise pointing. It is then better to film with a higher rate of 120 or 240 frames per second. FizziQ recognizes the different cadences but we will make sure in the analysis that the time difference between the images is respected. This is done during the pointing sequence.
7. Check nothing is missed
Before starting to record, it is best to make sure that all parts of the movement you want to record are within the scope of the device. We must both have a plan tight enough for the score to be done in detail, but wide enough to have the beginning and end of the sequence.
Have a good shooting!
To know more about Video Motion Analysis with a smartphone, also known as ViMAS (Video Movement Analysis Using a Smartphone), check out our dedicated article : Mastering Video Analysis in Physics: A Comprehensive Guide
To learn more about kinematic analysis, you can watch Jean-Michel Courty's excellent video for Billes de Sciences on the subject.
You will find examples of videos that you can download in our library of kinematics videos To learn more about using FizziQ for kinematic analysis, visit our Knowledge Base.
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