Vernier Video Physics for iOS brings physics video analysis to the iPhone, iPod touch, and iPad.
Getting Started with Video Physics
Tips for Video Capture
- Do not move the camera. Analysis assumes the camera is fixed in position.
- The object in motion should remain approximately in a plane perpendicular to the viewing direction.
- Know the dimensions of an object (such as a ruler) in the same plane as the motion. You will need this to scale the video.
Frequently Asked Questions
- What is Video Physics, and who is Vernier Software & Technology?
- Vernier Video Physics is the first iOS app from Vernier Software & Technology. We’ve been in the educational technology business for nearly 30 years, and are an established leader in the field of sensor-based data collection for hands-on science classes. Our flagship software Logger Pro includes a video analysis feature.
- What is video analysis?
- Video analysis is a process of using a short video of a moving object to create motion graphs for that object. The video must be very simple, with no panning or zooming. The object motion must be in a plane perpendicular to the viewing direction. An object of known size in that plane of motion is required to scale the video to physical units such as meters or feet. Even within these restrictions, many interesting motions can be analyzed.
- How do I get started with Video Physics?
A good place to start is the basketball shot video. Tap the “plus” button and choose “Sample Videos.” Select the basketball shot video and play it. Note that the ball follows a parabolic arc, and bounces once. Also note that there is a two-meter stick on the floor, in the plane of the motion.
Now set the video to a frame where the ball has just left the shooter’s hands. If necessary, select the point marking tool. Touch the screen to move the cursor. You can touch anywhere and drag to move the cursor. Position the cursor over the ball. Tap the screen to mark a point. Two things will happen: the point is marked, and the video advances one frame.
Now move the cursor to the new position of the ball, and tap with a second finger. Repeat to follow the ball through its trajectory. If you run out of room moving the cursor, just pick up your first finger and set it down where there is room.
Next, set the scale. Tap the scale tool (double arrow) and use the cursor to locate one end of the two-meter stick. Tap to mark it, just like you marked the ball locations. Mark the other side. You’ll see a place to enter the length of the scale; in this case, enter 2 and m for two meters. This will give Video Physics the information needed to properly scale the graphs.
Touch the graph button in the upper right. You’ll see a graph of Y vs. X, which is the trajectory of the ball. Swipe to see the X and X velocity as a function of time, and again to see the corresponding Y graphs. These graphs describe the moment-by-moment position of the basket ball. Notice that the Y vs. time graph is parabolic, while the X vs. time graph is linear. Why is that? (We’ll let you answer, because we are good physics teachers and won’t do the work for you.) The Y velocity vs. time graph is linear. Is there something special about the slope of that line?
Video Physics lets you email your video and analysis to a computer, where you can open the files in Vernier’s Logger Pro software. Logger Pro has curve fitting and other tools to get more out of your work. You can also share your analyzed video to Facebook, or save it to your camera roll. In either case, the video is shown with your marked points, and the graphs are appended to the end of the video.
- How do I mark points?
- Move the cursor by touching anywhere on the screen; you don’t have to touch the cursor itself. When the cursor is in the desired position, tap anywhere on the screen. It helps to put the iPhone or iPod on a table, rather than using it hand-held.
- My finger is on top of what I’m trying to mark, so I can’t see it!
- You can move the cursor from anywhere on the screen. Try dragging your finger on the screen a bit to the left or right of the target cursor. You’ll see that you can direct the cursor without obscuring the tracked object.
- I messed up. How do I fix a point marker?
- To move a marked point, just go back to that frame and repeat the mark.
- How I do delete a marked point?
- Use the video controller to move to the desired frame. The current point will be in yellow. Tap and hold; a popup will let you delete the point, or to select all points. If you select all, you can then delete them all. Be careful; you can’t get your marked points back.
- I can’t see how to play a video.
- The controls may be hidden. Tap the bottom edge of the screen (you’ll see the top of the controls hiding there) and the controls will slide back out.
- Can I zoom in to mark points?
- Yes! Try pinching and dragging to zoom the video and change its position. This is great for iPhone and iPod screens.
- How do I rename a Video Physics project?
- Tap Edit, and then tap the project to rename. Enter the new name, and tap Done.
- How do I delete a Video Physics project?
- Go to My Videos, and swipe across the project to be deleted. Tap Delete.
- What kind of things can be used to scale the video?
- To set the proper scale for graphs, you have to have some known dimension in the plane of the motion. This might be the object itself, such as the length of a car or the diameter of a ball. It could also be a meter stick, but be sure the stick is the same plane as the motion. In front or behind is not ok.
- What kind of videos can be analyzed?
- Video analysis in Video Physics requires videos that do not pan or zoom depict a motion in a plane perpendicular to the view direction contain an object of known dimension in the plane of the motion for scaling.
- My device meets the system requirements but does not have a camera. What can I do with it?
- You can transfer videos via iTunes file sharing, email or the Photo Library. See instructions on transferring video to devices that cannot record video »
- How do I share videos?
Save video to your camera roll (see system requirements)
Video Physics will create a new video containing the marked points and the associated graphs, and then save it to your camera roll. You can view or email the video there. You can even post to YouTube. Only landscape videos can be exported to the photo library.
Email Logger Pro file
Video Physics will create an email with attached video and Logger Pro file. On receipt, copy the attachments to a convenient location, and open the Logger Pro file.
- Save video to your camera roll (see system requirements)
- How many objects will Video Physics track?
- One. To track multiple objects, continue your analysis in Logger Pro.
- How do I avoid blurred images in videos?
- Use lots of light. Outdoors is good.
- Any other hints for good videos?
- Hold the camera steady.
- Keep the background plain so you can see the object.
- If you get streaks, use more light.
- Keep the plane of motion parallel to the plane of the camera lens.
- Have something of known length in plane of motion for scale.
- Will Video Physics do curve fits?
- No. Send your analysis to Graphical Analysis for iPad or Logger Pro to add curve fits.
- What about the other sample videos?
There are other sample videos. The Baseball Pitch lets you track the ball (look closely!). You can look up the distance between the pitcher mound and home plate and use that to scale the video. How fast was that pitch? The Segway video lets you measure the acceleration of a Segway. Use the meter stick on the ground to set the scale. The turntable video will let you explore the descriptions of circular motion. Before you look at your graphs, predict what a graph of X vs. time will look like for a point on the edge of the turntable. The caliper in the video has a 10 cm distance marked with pink tape.
These videos should give you ideas for your own exploration. You can take a new video right there inside Video Physics, or you can open an existing video in your Photos collection.
- That baseball pitch video is cool, but I see problems with it. Tell me more about it.
We wanted to share the baseball video with you despite its shortcomings. Besides, we’re sure you can do even better on your own.
The plane of the ball’s motion is not perfectly perpendicular to the view, since the mound is farther from the camera than is the home plate. That means that there will be some scaling error, so that the ball velocity will be underestimated near the pitcher, and overestimated near home plate. That’s ok, if we’re just getting a rough idea of the ball speed. The perspective explains why the X velocity vs. time graph is increasing in magnitude. The perspective also means that the Y graphs are not useful.
It’s usually very hard to get videos of a fast-moving object. We were a bit surprised that this video worked out at all, but we had the light going for us. We used an iPhone 4 camera, and the baseball field was in brilliant Oregon sunlight. That means the camera’s effective shutter speed is very short, so that the ball is caught clearly. Still, it’s hard to see the ball, so look closely.
There are a couple of frames where you can’t see the ball clearly because it is against a white background of a player’s uniform or the baseline. You can either skip those frames, or make a good guess as to where is was.
- Do you have any ideas for other cool videos to collect?
- Amusement Park Rides
- Cars or trains at intersections
- An airplane taking off
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